Kansas Fertilizer Research 2019

Report on agricultural research with fertilizers at Kansas State University.


Introduction
Tall fescue is the major cool-season grass in southeastern Kansas. Perennial grass crops, as with annual row crops, rely on proper fertilization for optimum production; however, meadows and pastures are often under-fertilized and produce low quantities of low-quality forage. Even when new stands are established, this is often true. The objective of this study was to determine whether N, P, and K fertilization improves yields during the early years of a stand.

Experimental Procedures
The experiment was established on two adjacent sites in the fall of 2012 (Site 1) and 2013 (Site 2) at the Parsons Unit of the Kansas State University Southeast Agricultural Research Center. The soil at both sites was a Parsons silt loam soil with initial soil test values of 5.9 pH, 2.8% organic matter, 4.2 ppm P, 70 ppm K, 3.9 ppm NH 4 -N, and 37.9 ppm NO 3 -N in the top 6 inches at Site 1; and 6.5 pH, 2.2% organic matter, 6.7 ppm P, 58 ppm K, 6.8 ppm NH 4 -N, and 12.3 ppm NO 3 -N in the top 6 inches at Site 2. The experimental design was a split-plot arrangement of a randomized complete block. The six whole plots received combinations of P 2 O 5 and K 2 O fertilizer levels allowing for two separate analyses: 1) four levels of P 2 O 5 consisting of 0, 25, and 50 lb/a each year and a fourth treatment of 100 lb/a only applied at the beginning of the study; and 2) a 2 × 2 factorial combination of two levels of P 2 O 5 (0 and 50 lb/a) and two levels of K 2 O (0 and 40 lb/a). Subplots were four levels of N fertilization consisting of 0, 50, 100, and 150 lb/a. Phosphorus and K fertilizers were broadcast applied in the fall as 0-46-0 (triple superphosphate) and 0-0-60 (potassium chloride). Nitrogen was broadcast applied in late winter as 46-0-0 (urea) solid. Fourth-year sampling and harvest dates from each site were as follows. Early growth yield as an estimate of grazing potential in early spring was taken at E2 (

Results and Discussion
Fourth-year production of tall fescue was measured at Site 1 in 2016 and at Site 2 in 2017. At site 1 in 2016, early yield at the E2 (jointing) growth stage, measured to estimate forage available if grazed early, was increased with 50 lb P 2 O 5 /a (Table 1), and was increased with N rates of 100 or 150 lb/a above yield with no N added. At the R4 stage of hay harvest in 2016, yield was increased by P fertilization, but with no difference between rates. Nitrogen fertilizer additions up to 150 lb/a increased R4 hay yield. Fall yields were unaffected by P fertilization. Apparent mineralization during the summer resulted greater fall yield with no N as compared to the 50 and 100 lb N/a rates applied in late winter. Total yield was maximized with P fertilization and N applied at 150 lb/a.
For the fourth year of production at Site 2 (2017), yield was mainly affected by N rate. Sampling at E2 and R4 and fall harvest yields were not affected by P fertilization (Table  2) and response to K fertilization was marginal (data not shown). Increasing N rates tended to increase yield at the E2 sampling, R4 hay harvest, and total (R4 + fall) yield, especially with K fertilization (data not shown), but response was less defined at the fall harvest (Table 2). Total yield averaged less than 3.5 ton/a, even at the 150 lb/a N rate.

Experimental Procedures
A split-plot design with four replications was initiated in 1983 with tillage system as the whole plot and N treatment as the subplot. In 2005, the rotation was changed to begin a short-season corn/wheat/double-crop soybean sequence. Use of three tillage systems (conventional, reduced, and no-till) continued in the same areas used during the previous 22 years. The conventional system consisted of chiseling, disking, and field cultivation. Chisel operations occurred in the fall preceding corn or wheat crops. The reducedtillage system consists of disking and field cultivation prior to planting. Glyphosate (Roundup) was applied to the no-till areas. The four N treatments for the crop were: no N (control), broadcast urea ammonium nitrate (UAN; 28% N) solution, dribble UAN solution, and knife UAN solution at a 4 in. depth. The N rate for the corn crop grown in odd years was 125 lb/a. Corn was planted on April 11, 2017.

Results and Discussion
Overall, yields were high in 2017. Tillage did not statistically affect corn yields ( Figure  1). In general, adding N by any placement method approximately doubled the yield obtained without N. However, corn yield in 2017 was not affected by N placement method or by the interaction of tillage by N treatments. Timing of Side-Dress Applications of Nitrogen for Corn in Conventional and No-Till Systems Introduction Environmental conditions vary widely in the spring in southeastern Kansas. As a result, much of the N applied prior to corn planting may be lost before the time of maximum plant N uptake. Side-dress or split applications to provide N during rapid growth periods may improve N use efficiency while reducing potential losses to the environment. The objective of this study was to determine the effect of timing of side-dress N fertilization compared with pre-plant N applications for corn grown on a claypan soil.

Experimental Procedures
The experiment was established in spring 2015 on a Parsons silt loam soil at the Parsons unit of the Kansas State University Southeast Agricultural Research Center. The experiment was a split-plot arrangement of a randomized complete block design with four blocks (replications). Whole plot tillage treatments were conventional tillage (chisel, disk, and field cultivate) and no tillage. Sub-plot nitrogen treatments were six pre-plant/ side-dress N application combinations that include 1) a no-N control, 2) 150 lb N/a applied pre-plant, 3) 100 lb N/a applied pre-plant with 50 lb N/a applied at the V6 (six-leaf) growth stage, 4) 100 lb N/a applied pre-plant with 50 lb N/a applied at the V10 (ten-leaf) growth stage, 5) 150 lb N/a applied pre-plant with 50 lb N/a applied at the V6 growth stage, and 6) 150 lb N/a applied pre-plant with 50 lb N/a applied at the V10 growth stage. The N source for all treatments was liquid urea-ammonium nitrate (28% N) fertilizer. Pre-plant N fertilizer was applied on March 16, 2017, side-dress N at V6 on May 25, 2017, and side-dress N at V10 on June 12, 2017, to appropriate plots. All N was broadcast applied with 7-stream pattern fertilizer nozzles. Corn was planted on April 11 and harvested on September 11, 2017.

Results and Discussion
In 2017, corn yielded 18 bu/a more with conventional tillage than with no-tillage, likely because of 16% greater stand (Table 1). Adding N fertilizer, generally, more than doubled yields obtained in the no-N control. Splitting the N fertilizer to apply 100 lb N/a preplant followed by 50 lb N/a at the V6 or V10 growth stages improved yields by more than 15 bu/a greater than all N applied pre-plant. Adding 50 lb N/a extra at the V6 growth stage to a 150 lb N/a preplant application did not improve yields more than that obtained with 150 lb N/a applied split pre-plant and side-dress. However, delaying the extra 50 lb N/a side-dress application to the V10 stage improved yield by nearly 20 bu/a. These effects of N timing on corn yield in 2017 appeared to be related to the combined responses in kernel weight, ears/plant and kernels/ear.

Introduction
Increased fertilizer prices in recent years, especially noticeable when the cost of phosphorus spiked in 2008, have led U.S. producers to consider other alternatives, including manure sources. The use of poultry litter as an alternative to fertilizer is of particular interest in southeastern Kansas because large amounts of poultry litter are imported from nearby confined animal feeding operations in Arkansas, Oklahoma, and Missouri. Annual application of turkey litter can affect the current crop, but information is lacking concerning any residual effects from several continuous years of poultry litter applications on a following crop. This is especially true for tilled soil compared with no-till because production of most annual cereal crops on the claypan soils of the region is often negatively affected by no-till planting. The objective of this study was to determine if the residual from fertilizer and poultry litter applications under tilled or no-till systems affects soybean yield and growth.

Experimental Procedures
A water quality experiment was conducted near Girard, KS, on the Greenbush Educational facility's grounds from spring 2011 through spring 2014. Fertilizer and turkey litter were applied prior to planting grain sorghum each spring. Individual plot size was 1 acre. The five treatments, replicated twice, were: Control -no N or P fertilizer or turkey litter -no tillage; Fertilizer only -commercial N and P fertilizer -chisel-disk tillage; Turkey litter, N-based -no extra N or P fertilizer -no tillage; Turkey litter, N-based -no extra N or P fertilizer -chisel-disk tillage; and Turkey litter, P-based -supplemented with fertilizer N -chisel-disk tillage. Starting in 2014 after the previously-mentioned study, soybean was planted with no further application of turkey litter or fertilizer. Prior to planting soybean, tillage operations were done in appropriate plots as in previous years. A sub-area of 20 × 20 ft near the center of each 1-acre plot was designated for crop yield and growth measurements. Samples were taken for dry matter production at V3-V4 (approximately 3 weeks after planting), R2, R4, and R6 growth stages. Yield was determined from the center 4 rows (10 × 20 ft) of the sub-area designated for plant measurements in each plot.

Results and Discussion
In 2017, the residual effects of turkey litter and fertilizer amendments affected soybean yield, pods/plant, and seeds/pod ( Table 1). The two treatments which had previously received a high application rate of turkey litter based on N requirements, regardless of tillage system, resulted in greater yields than from plots that had received low rates of turkey litter (P-based), commercial fertilizer, or no fertilizer N or P. The number of pods/plant and the number of seeds/pod were greater where N-based turkey litter had been applied than in the other residual treatments. Dry matter production was marginally affected by residual treatment through the R4 growth stage. However, at R6, dry matter production was greatest where turkey litter had previously been applied on an N-basis (high rate) and incorporated.   Control, no turkey litter or N and P fertilizer with no tillage; TL-N, N-based turkey litter application with no tillage; TL-N-C, N-based turkey litter application incorporated with conventional tillage; TL-P-C, P-based turkey litter application and supplemental N application incorporated with conventional tillage; and Fert-C, commercial fertilizer incorporated with conventional tillage.

Introduction
This study was initiated in 1961 to determine responses of continuous grain sorghum grown under flood irrigation to N, P, and K fertilization. The study is conducted on a Ulysses silt loam soil with an inherently high K content. The irrigation system was changed from flood to sprinkler in 2001.

Procedures
This field study is conducted at the Tribune Unit of the Kansas State University Southwest Research-Extension Center. Fertilizer treatments initiated in 1961 are N rates of 0, 40, 80, 120, 160, and 200 lb/a N without P and K; with 40 lb/a P 2 O 5 and zero K; and with 40 lb/a P 2 O 5 and 40 lb/a K 2 O. All fertilizers are broadcast by hand in the spring and incorporated before planting. The soil is a Ulysses silt loam. Grain sorghum (Pioneer 85G46 in 2009-2011, Pioneer 84G62 in 2012-2014, Pioneer 86G32 in 2015, Pioneer 84G62 in 2016-2017, and Pioneer 85P44 in 2018 was planted in late May or early June. Irrigation is used to minimize water stress. Sprinkler irrigation has been used since 2001. The center two rows of each plot are machine harvested after physiological maturity. Grain yields are adjusted to 12.5% moisture. Grain samples were collected at harvest, dried, ground, and analyzed for N, P, and K concentrations. Grain N, P, and K content (lb/bu) and removal (lb/a) were calculated. Apparent fertilizer N recovery in the grain (AFNR g ) was calculated as N uptake in treatments receiving N fertilizer minus N uptake in the unfertilized control divided by N rate. The same approach was used to calculate apparent fertilizer P recovery in the grain (AFPR g ) and apparent fertilizer K recovery (AFKR g ).

Results
Grain sorghum yields in 2018 were 5% lower than the 10-year average (Table 1). Nitrogen alone increased yields 44 bu/a, while P alone increased yields less than 10 bu/a. However, N and P applied together increased yields up to 67 bu/a. Averaged across the past 10 years, N and P applied together increased yields up to 75 bu/a. In 2018, 40 lb/a N (with P) produced about 88% of maximum yield, which is greater than the 10-year average of 85%. The 10-year average for 80 lb/a N (with P) and 120 lb/a N (with P) was 94 and 95% of maximum yield, respectively. Sorghum yields were not affected by K fertilization, which has been the case throughout the study period.

Long-Term Nitrogen and Phosphorus Introduction
This study was initiated in 1961 to determine responses of continuous corn and grain sorghum grown under flood irrigation to N, P, and potassium (K) fertilization. The study is conducted on a Ulysses silt loam soil with an inherently high K content. No yield benefit to corn from K fertilization was observed in 30 years, and soil K levels remained high, so the K treatment was discontinued in 1992 and replaced with a higher P rate.

Procedures
This field study is conducted at the Tribune Unit of the Kansas State University Southwest Research-Extension Center. Fertilizer treatments initiated in 1961 are N rates of 0, 40, 80, 120, 160, and 200 lb/a without P and K; with 40 lb/a P 2 O 5 and zero K; and with 40 lb/a P 2 O 5 and 40 lb/a K 2 O. The treatments were changed in 1992; the K variable was replaced by a higher rate of P (80 lb/a P 2 O 5 ). All fertilizers were broadcast by hand in the spring and incorporated before planting. The soil is a Ulysses silt loam. The corn hybrids [DeKalb 61-69 (2009) The center two rows of each plot are machine harvested after physiological maturity. Grain yields are adjusted to 15.5% moisture. Grain samples were collected at harvest, dried, ground, and analyzed for N and P concentrations. Grain N and P content (lb/bu) and removal (lb/a) were calculated. Apparent fertilizer N recovery in the grain (AFNR g ) was calculated as N uptake in treatments receiving N fertilizer minus N uptake in the unfertilized control divided by N rate. The same approach was used to calculate apparent fertilizer P recovery in the grain (AFPR g ). Grasshoppers were treated by aerial application of insecticide.

Results
Corn yields in 2018 were 15% higher than the 10-year average (Table 1). Nitrogen alone increased yields 76 bu/a, whereas P alone increased yields 17 bu/a. However, N and P applied together increased corn yields up to 169 bu/a. Maximum yield was obtained with 160 lb/a N with 80 lb/a P 2 O 5. Corn yields in 2018 (averaged across all N rates) were 9 bu/a greater with 80 than with 40 lb/a P 2 O 5 .

Summary
Occasional tillage ahead of winter wheat planting could alleviate herbicide-resistant weeds, redistribute soil acidification, and improve seedbed at wheat planting. The objective of this study is to determine occasional tillage and nitrogen (N) fertilizer application effects on winter wheat, and grain sorghum yields and soil quality in a wheat-sorghum-fallow cropping system. Treatments were three tillage practices: 1) continuous no-tillage (NT); 2) continuous reduced-tillage (RT); and 3) single tillage operation every 3 years (June-July) ahead of winter wheat planting [occasional tillage (OT)]. The sub-plot treatments were assigned to four N fertilizer rates (0, 40, 80 and 120 lb/a of N). Preliminary results showed tillage had no effect on winter wheat grain yield. Applying N fertilizer increased wheat yield, ranging from 21 bu/a with no N fertilizer to 29 bu/a when N fertilizer was applied at 120 lb/a of N. Tillage and N fertilizer effects on grain sorghum yield varied over the 2 years of the study. Grain sorghum yields in 2017 decreased with RT but tillage had no effect on sorghum yields in 2018. Averaged across tillage and years, sorghum grain yield was 54 bu/a with no N fertilizer and 84 bu/a when N was applied at 120 lb/a of N. Both sorghum and winter wheat grain yields obtained with 80 lb/a of N were not different from those with 120 lb/a of N, suggesting 80 lb/a of N may be adequate for both crops.

Introduction
Adoption of NT practices during fallow by many producers in the central Great Plains (CGP) has increased the quantity of residues retained on the soil surface, and soil moisture storage. This has allowed for cropping intensification in dryland systems in the CGP from winter wheat-fallow to winter wheat-summer crop-fallow or a more intensified cropping system with no fallow depending on soil water availability. The benefits of NT include reduction in soil erosion, increased soil organic matter accumulation, improved soil structure, and increased soil water storage.
Despite these benefits, stratification of soil nutrients, organic matter, and pH tend to develop near the soil surface in long-term continuous NT systems. In addition, the lack of effective herbicides for perennial grass weeds-such as three-awn grass (Aristida purpurea Nutt.) and tumble windmill grass (Chloris verticillata Nutt.) -and the emergence of glyphosate-resistant weeds pose challenges in NT crop production. Also in drier years, the upper layer (0-2 inches) of soils in NT tends to be "hard" and presents a challenge to placing seed in subsoil moisture at the time of wheat planting. This may cause poor plant establishment and reduce winter wheat yields. Occasional tillage of NT soils may be necessary to alleviate herbicide-resistant weed issues, redistribute soil acidity, and improve seedbed at wheat planting. Research objectives are to determine the impacts of OT and N application on crop yields and soil water availability, and long-term effects of OT on soil health and herbicide-resistant weeds.

Procedures
Field experiments were initiated in spring 2017 at the Kansas State University Agricultural Research Center near Hays, KS, to address the previously mentioned objectives. Study design is a split-split-plot with three replications in a randomized complete block design. Main plots were three crop phases of a wheat-sorghum-fallow, sub-plot treatments were three tillage practices: 1) continuous NT; 2) continuous RT; and 3) single tillage operation every 3 years (June-July) ahead of winter wheat planting (OT). The sub-sub-plots were assigned to four N fertilizer application rates (0, 40, 80, and 120 lb/a of N). The reduced tillage treatments had two to three tillage operations during fallow ahead of wheat planting and one tillage operation prior to sorghum planting. All tillage operations were done with a sweep-plow to a depth of 4-to 6-inches. Each phase of the crop rotation, tillage, and N fertilizer treatment is implemented in each year of the study. Winter wheat and sorghum grain yields were determined by harvesting a 5 × 80 ft area from the center of each plot using a small plot combine. Statistical analysis with the PROC MIXED procedure in SAS version 9.4 (SAS Inst., Cary, NC) was used to examine winter wheat and grain sorghum yields as a function of tillage and N fertilizer application.

Winter Wheat Grain Yield
Winter wheat grain yield in 2018 was not affected by tillage (Figure 1a). Averaged across N rates, wheat grain yield was 25 bu/a with NT or OT, and 23 bu/a with RT. Applying N fertilizer did increase wheat grain yield. Across tillage treatments, grain yield ranged from 21 bu/a with no N fertilizer to 29 bu/a when N fertilizer was applied at 120 lb/a of N. However, wheat grain yield was not different when N was applied at 80 lb/a of N or 120 lb/a of N (Figure 1b).
Tillage effects on sorghum grain yield varied over the 2 years. In 2017, sorghum grain yields with NT or OT were not different. However, RT operations reduced sorghum grain yield compared to the other tillage treatments ( Figure 2). Tillage had no effect on grain sorghum yields in 2018, possibly due to abundant precipitation during the sorghum growing season in 2018. Similarly, sorghum response to N fertilizer application differed over the 2 years. Application of N fertilizer increased sorghum yields in 2017, but grain yields produced with 40 lb/a of N were similar to that achieved with greater N rates. In the 2018 growing season, applying N fertilizer resulted in a linear increase in sorghum grain yield. Averaged across tillage treatments, sorghum grain yield ranged from 52 bu/a with no N fertilizer application to 91 bu/a when 120 lb/a of N was applied (Figure 3). The differences in N response between 2017 and 2018 growing seasons were because of the differences in precipitation amount in the 2 years that affected amount of available soil water for sorghum production. Across the 2 years and tillage treatments, applying N fertilizer increased grain yield from 54 bu/a with the check treatment (no N applied) to 84 bu/a with 120 lb/a of N. However, grain yield with 80 lb/a of N (79 bu/a) was not different from that obtained with the highest N rate of 120 lb/a of N.

Summary
Emerging challenges in continuous no-till (NT) systems require developing flexible management strategies that will minimize the impacts of herbicide resistant (HR) weeds and nutrient stratification on soil and crop productivity. This study evaluated the effectiveness of strategic tillage (ST) operations as an option to redistribute soil nutrients and acidity, control perennial grass and HR weeds, and improve crop yields following tillage of an otherwise long-term NT soil. Treatments were five crop rotations: 1) continuous winter wheat (WW); 2) wheat-fallow (WF); 3) wheat-sorghumfallow (WSF); 4) continuous sorghum (SS); and 5) sorghum-fallow (SF) as main plots. Subplots were reduced tilled (RT), continuous NT, and ST of long-term NT. Grass and herbicide resistant weeds were reduced with tillage. Irrespective of crop rotation, soil water content at wheat planting was significantly less with RT treatments compared to NT or ST. Soil water content with NT was not different from that of ST under cropping systems with fallow (WF or WSF). Tillage (ST or RT) reduced soil water content at wheat planting in WW system. Winter wheat grain yields decreased with increasing cropping intensity, WF (26-48 bu/a) > WSF (22-33 bu/a) > WW (15-19 bu/a). Averaged across years and crop rotations, wheat yield with ST was 30 bu/a, which was greater than the NT (23 bu/a) or RT (28 bu/a) systems, mostly due to better weed control and increased nutrient availability. Sorghum grain yield over the 2 years with ST (63 bu/a) was not different from that of NT (61 bu/a), but were both greater than that of RT (54 bu/a). Increasing cropping intensity reduced sorghum grain yield, average grain yield with SF was 73 bu/a, similar to WSF (68 bu/a), but greater than SS (38 bu/a). Tillage had no effect on soil bulk density. However, increasing cropping intensity lowered the bulk density measured in the upper 0 to 2 in. of the soil. Tillage and crop rotation effects on soil organic matter (SOM), pH, and nutrient concentrations occurred only in the top 0-to 2-in. depth. The SOM, iron (Fe), and manganese (MN) concentrations were greater in soils under WW compared to WF or WSF. Soil pH and potassium (K) were least in soils under WW. The SOM concentration in the top 0 to 2 in. with NT was 3.34%, which was similar to that of soil under ST (3.02%) but both were greater than RT (2.65%). Nitrate-N concentration increased with ST but ammonium-N concentration was greatest in soils under NT. Our results suggest ST could provide a mitigation option for HR weeds in NT crop production with little impact on crop yields and soil chemical properties.

Introduction
No-tillage (NT) systems provide several benefits to dryland crop production in the semiarid central Great Plains (CGP). These include improvements to soil health, reduced wind erosion, fewer energy inputs, increased retention of soil moisture, and improved crop yields. Despite these benefits, maintaining continuous NT and the associated soil conservation benefits are at risk due to a lack of effective control of HR weeds, as well as issues of compaction and stratification of soil pH and nutrients. Strati-fication of soil nutrients and soil acidity could reduce nutrient availability and uptake by crops and increase the chances of nitrogen and phosphorus losses in surface runoff.
In addition, the lack of effective herbicides to control perennial grass weeds such as three-awn grass (Aristida purpurea Nutt.) and tumble windmill grass (Chloris verticillata Nutt.), and the advent of herbicide resistant weeds such as kochia (Kochia scoparia L.) and Palmer amaranth (Amaranthus palmeri S. Watson) pose challenges in NT crop production. With low grain prices and the high cost of controlling HR weeds, some producers are returning to tillage as a strategic management tool.
Strategic tillage (ST) with a sweep plow timed when soil erosion risk is low in an otherwise NT cropping system could help manage HR weed populations and reduce stratification of soil properties. After the one-time tillage operation, the field goes back to NT production. This ST approach could increase productivity and profitability of dryland cropping systems in the region. However, the soil health impacts of ST are unclear particularly in water-limited environments of the CGP where susceptibility to wind erosion can be high.
Few studies have investigated the effects of ST on soils that have been in continuous NT (> 40 years) in dryland conditions in the CGP. Our objectives were to determine the effects of ST in long-term NT systems on 1) soil water content at winter wheat planting; 2) winter wheat and grain sorghum yields; 3) effectiveness of ST to redistribute soil nutrients, reduce soil acidity, and control perennial grass and herbicide resistant weeds; and 4) determine soil quality following tillage of an otherwise long-term NT soil.

Procedures
This study was conducted using long-term tillage and crop rotation experiment plots established in 1976 at the Kansas State University Agricultural Research Center near Hays, KS. The experimental design was a randomized complete block with three replications in a split-plot treatment structure. Main plots were five crop rotations [continuous winter wheat (WW), wheat-fallow (WF), wheat-sorghum-fallow (WSF), continuous sorghum (SS), and sorghum-fallow (SF)] and two tillage treatments (RT and NT) as sub-plots. Every phase of each crop rotation and tillage system combination was present in each replication for each year of the study. The study was modified in the summer of 2016 to three tillage treatments [RT, continuous NT, and strategic tillage (ST) of NT] by splitting the long-term NT plots into two equal plots of 20-ft wide by 80-ft long. One half was left in continuous NT and the other half was tilled. The ST plots were tilled twice, first with a sweep plow to a 3-in. depth followed by a second tillage operation 3 days later to 6-in. depth, also with a sweep plow. All tillage operations in the wheat rotations were performed in July prior to winter wheat planting in October. For crop rotations involving sorghum, tillage operations were done in May before sorghum planting in June. Tillage in the RT treatments were accomplished with the same tillage implement to 6-to 8-in. depth. Two to three tillage operations were usually done in the RT plots over the fallow period.
Soil water content at winter wheat planting was determined gravimetrically to 4 ft, in 6-in. depth increments in 2016 and 2017. Two soil cores were taken from each plot and data averaged for a single soil water content measurement. Winter wheat and sorghum grain yields were determined by harvesting a 5 × 80 ft area from the center of each plot using a small plot combine. Soil samples were taken from 0 to 2, 2 to 6, 6 to 12 in. soil depths after tillage operations in 2017 only. These samples were analyzed for changes in bulk density, soil organic carbon (SOC), dry aggregate size distribution, and soil nutrients. The SOC was multiplied by a factor of 2 (because no calibrated conversion factor is available for this soil) and reported as SOM concentration.

Weeds, Soil Water Content, and Bulk Density
In general, broadleaf and grass weeds were significantly less with RT and ST compared to the NT treatments (data not shown). Tillage × crop rotation interaction had a significant effect on soil water content measured at winter wheat planting. Regardless of crop rotation, soil water content with NT was similar to that of ST but were both greater than that measured with RT in crop rotation systems that had fallow ( Figure  1). However, with WW system, tillage operation as either ST or RT reduced soil water at winter wheat planting compared to NT (Figure 1). Averaged across crop rotations, profile soil water content was 13.4 in. with NT or ST, and 12.6 in. with RT over the 2 years. In general, water content decreased with increasing cropping intensity, mostly due to increased crop water use. Averaged across the 2 years and tillage treatments, profile soil water content with WF was 13.7 inches, which was greater than WSF (13.2 inches) or WW (12.4 inches).
Soil bulk density measured within the top 12 in. of the soil was not different among tillage systems. Across crop rotations and sampling depth, bulk density averaged 1.16 g cm -3 with NT and 1.13 g cm -3 with ST or RT. However, crop rotation × depth interaction had a significant effect on bulk density. In general, bulk density within the top 0 to 6 inches decreased with increasing cropping intensity. The continuous wheat treatment had the lowest bulk density at 0 to 2 in., and 2 to 6 in. depth (Table 1), possibly due to greater contribution of plant residue input onto the soil surface. Bulk density was no different among the crop rotation systems beyond the 6-in. depth.

Soil pH and Nutrient Concentrations
Tillage system had no effect on soil pH, which averaged 5.5 for NT, 5.6 with ST, and 5.7 with RT at the upper 0 to 2 in. soil depth. Crop rotation × sampling depth interaction had a significant effect on soil pH. Regardless of crop rotation system, pH at the upper 0 to 2 in. was markedly lower than that measured in the subsurface. Averaged across tillage treatments, soil pH at the 0 to 2 in. depth was lowest in the WW production system (Table 1), possibly because of annual N fertilizer application and mineralization of SOM in this treatment. Soil pH measured below 2 in. depth was not different among crop rotations. The SOM concentration was significantly affected by crop rotation and tillage, but mostly within the top 0 to 2 in. Across tillage, SOM measured in the upper surface was 2.72% for WF, 2.74% for WSF, and 3.55% for WW. The differences were due to differences in crop residue addition that affected SOM accretion in the surface soil. When averaged across crop rotations, SOM concentration measured in the upper soil surface with ST was 3.02%, which was similar to 3.34% measured in soil under long-term continuous NT but were both greater than that with RT (Table 2).
Tillage system had no effect on SOM concentration beyond the top 0 to 2 in. soil depth.
Tillage or crop rotation effects on soil nutrient concentrations were limited to the upper 0 to 2 in. of the soil. Soil K concentration in the upper surface decreased with WW compared to WF or WSF system. However, soil Fe and Mn concentrations increased with WW production system. Greater Mn and Fe concentration in soils under WW is possibly explained by the decrease in soil pH associated with the WW system that caused increased solubility of these cations. Soil P and Zn concentrations were not affected by tillage or crop rotation. Nitrate-N concentration measured in the upper soil surface increased under ST compared to NT or RT. This was possibly because of increased mineralization associated with tillage of the long-term NT soil. Expectedly, ammonium-N concentration was significantly greater in soils under NT (Table 2). However, soil K concentration increased in soils under RT compared to NT or ST system.

Winter Wheat and Grain Sorghum Yield
Winter wheat grain yield differed over the two years of the study. Crop rotation × year interaction had effect on winter wheat grain yield. Regardless of crop rotation, winter wheat grain yield in 2018 was significantly less than that achieved in 2017 ( Figure 2). Averaged across tillage and crop rotation, wheat yield averaged 33.3 bu/a in 2017 and 20.7 bu/a in 2018. The differences were due to spring drought conditions in 2018. Winter wheat grain yields decreased with increasing cropping intensity, WF (26-48 bu/a) > WSF (22-33 bu/a) > WW (15-19 bu/a), which was expected due to decreased soil water availability for crop production when cropping intensity increased.
Similarly, tillage intensity had significant (P = 0.0006) effect on wheat grain yield. Across the 2 years and crop rotations, winter wheat yield with NT was 23 bu/a, which was less than the 30 bu/a obtained with ST or 28 bu/a with RT ( Figure 3a). This is possibly due to improved grass weed control with tillage operations that reduced weed competition and improved plant establishment. It is also plausible that tillage operations of long-term NT increased nutrient availability, particularly N (Table 1) in the ST plots compared to continuous NT or RT treatments.
Average sorghum grain yield in 2017 was 47 bu/a, less than the 72 bu/a in 2018. Grain yields were significantly affected by crop rotation (P = 0.0001) and tillage (P = 0.006). Sorghum grain yield with ST was not different from that of NT, but were both greater than that of RT (Figure 3b). Similar to winter wheat, increasing cropping intensity reduced sorghum grain yield. Average grain yield of SF was 73 bu/a, similar to WSF (68 bu/a) but greater than SS (38.1 bu/a).

Introduction
Sulfur plays many roles within the plant, from the synthesis of amino acids to formation of chlorophyll. Sulfur is supplied to plants through rainfall, soil organic matter and crop residue mineralization, or as part of organic or mineral fertilizers. Wheat takes up approximately 80% of the S before anthesis. Winter wheat planted after soybeans has become the preferred crop rotation in recent years for many producers in north-central Kansas. Due to the high removal of S by soybeans, lower organic matter mineralization in the spring, and the declining S deposition in the rainfall, symptoms of S deficiency are increasingly common in north-central Kansas. Requirements of S for wheat are generally low (80 bu/a crop removes 7 lb of S in the grain and another 15 lb of S in the straw). However, soybeans remove approximately 25 lb of S in the grain and stover in a 60 bu/a grain crop. Research is needed to determine the effects of S on wheat yield and grain quality in Kansas soils.
Proper N fertilization increases probability of higher tiller number and grain yield (Jaenisch et al., 2019;Lollato et al., 2019). Winter wheat is generally sink limited, and kernels per foot is a coarse regulator of increasing wheat grain yield. Potential kernels per meter are determined by Feekes 6 in the winter wheat growing season, and N deficiency at this time will result in decreased yield potential. Thus, matching N application with this critical growth stage is important for maximizing kernels per foot. Likewise, N concentration within the plant changes throughout the growing season according to biomass levels; therefore, N dilution curves help determine N deficiencies in crops.
Research is needed to determine the optimal N concentration and N:S ratios in plant tissue to maximize grain yield and quality in Kansas.

Procedures
The experiment was established in the fall of 2017 at the Kansas State University North Central Experiment Field in Belleville (moderately well-drained Crete silt loam, 0-1% slopes) and Agronomy North Farm in Manhattan (Kahola silt loam, rarely flooded, 0-1% slopes). No-till has occurred for 11 and 6 years in Manhattan and Belleville, respectively. Both locations were grown under rainfed conditions and were chosen as no-till wheat, which is commonly sown into soybean stubble at these locations in Kansas.
Treatments included four S rates (0, 10, 20, and 40 lb S) and three N rates (50, 100, and 150% of K-State recommendations for a 60 bu/a yield) which were applied to two wheat varieties (SY Monument and LCS Mint) in a 2 × 3 × 4 (variety × N rate × S rate) complete factorial structure. The experiment was arranged in a split-split-plot design with four replications. The varieties SY Monument and LCS Mint were selected for their differences in N uptake and N use efficiency. Nitrogen was applied as urea ammonium nitrate (28-0-0) and S was applied as ammonium thiosulfate (12-0-0-26S) using a pressurized CO 2 back sprayer with a three-nozzle spray boom. The specific streamer nozzles (SJ3-02-VP -SJ3-05-VP) varied due to the change in N and S rates. The N and S were applied in combination for specific treatments and application occurred at Feekes 4.
Wheat was sown no-till into soybean stubble directly after harvest with a Great Plains 506 no-till drill (7 rows spaced at 7.5 inches) with plot dimensions of 4.375-ft wide × 30-ft long at all locations. Seed was treated with 5 oz Sativa IMF Max across the whole study so fungicide or insecticide was not a limiting factor. Likewise, both varieties were sown at 1.5 million seeds due to the later planting date.
In 2017, soil samples were taken at sowing at each location for soil nutrient analysis. Samples were taken by a hand push probe at two depths, 0-6 and 6-24 in., and a total of 15 cores were pulled per depth and combined to represent a composed sample at each location. Weeds were controlled to ensure they were not limiting factors by a preand post-emergence herbicide application. Insect pressure was not experienced in 2018.

Weather
The 2017-18 wheat growing season can be classified as a cold and dry winter, to a cold and dry early spring, to a hot and dry late spring/early summer. The drought and cool temperatures kept the wheat crop dormant until late April. Likewise, the reduced rainfall in the spring reduced spring tillering and fertilizer incorporation, thus decreasing spikes per foot. For the season, 60 and 49% of the annual rainfall was received for Belleville and Manhattan, respectively. Temperatures were above normal for May and June, accelerating crop development and decreasing the grain filling period. Wheat yields ranged from 64-76 bu/a in Belleville and Manhattan.

Wheat Grain Yield
Across locations, increasing N rate increased wheat grain yield ( Figure 1) and the N by S rate interaction was measured. The 45 lb N/a with 0, 10, or 40 lb S resulted in the highest grain yield of 67 bu/a and the addition of 20 lb S decreased yield to 64 bu/a. The 87 lb N/a and all S rates yielded similarly to 73 bu/a. At the highest N rate (137 lb N/a), 0 or 20 lb N/a resulted in the highest grain yield of 79 bu/a; however, 10 or 40 lb S/a reduced grain yield to 76 bu/a.

Grain Protein
Following the same trend as grain yield, an increasing N rate increased grain protein.
Likewise, the S rate also increased protein but did not follow a linear trend as compared to N rate (Figure 2). The N by S rate interaction for protein concentration was measured. The 45 lb N/a with 10 lb S resulted in the highest protein concentration of 10.9%, and the addition of 0, 20, or 40 lb S decreased protein concentration to 10.6%, perhaps as a dilution effect from slightly higher grain yield. The 87 lb N/a with 10 lb S resulted in the highest protein concentration of 11.9%, and the addition of 0, 20, or 40 lb S decreased protein concentration to 11.6%. The highest N rate of 137 lb N/a with 0, 10, or 40 lb S resulted in the highest protein concentration of 12.6-12.8%; however, 20 lb S reduced protein concentration to 12.5%, again, perhaps due to increased yield in this treatment.

Preliminary Conclusions
Due to limitations of sites and years, it is difficult to make strong conclusions. However, with significant N by S rate interactions for both grain yield and protein concentration, the preliminary data suggest that a balanced nutrition is needed for both nutrients to maximize yield and protein. One existing trend was that increasing N increased grain yield and protein concentration, suggesting that N rate could have been further increased to maximize yield in the studied sites. However, Staggenborg et al. (2003) measured grain yield to plateau at 75 lb N/a in wheat planted after summer crops. Therefore, this warrants additional research to understand whether further increasing N is economically viable, and to better characterize N × S × variety interactions.

Introduction
Nitrogen is an essential element for optimum corn yields. After applied as fertilizer to the soil, N changes its chemical form and can be subject to potential loss. Nitrification is an important step in the N cycle and is promoted by the biological oxidation of ammonium to nitrite and nitrate. Conversion of NH 4 + -N to NO 3 --N increases the potential for nitrogen leaching due to the mobility of nitrate in the soil and can be readily lost from the plant rooting zone . The nitrification process can occur rapidly in warm, moist, well-aerated soils.
Nitrification inhibitors are chemicals that slow down or delay the nitrification process, thereby decreasing the possibility of large N losses before the fertilizer nitrogen is taken up by plants . The objective of this study was to evaluate the effect of NI on soil nitrate and ammonium content in the soil throughout the corn growing season.

Procedures
This study was conducted in four locations (Manhattan, Scandia, Rossville, and Ashland, KS) during the 2017 and 2018 crop seasons. Treatments were: 1) N fertilizer without nitrification inhibitor (control), and 2) N fertilizer treated with nitrification inhibitor. Anhydrous ammonia was applied at four rates 0, 100, 150, and 200 lb/a in early spring. Soil samples were taken at the V2, V4, V8, V12, R1, and R6 corn growth stages at two soil depths (0-12 and 12-24 in.). Soil samples were submitted to the K-State Research and Extension Soil Testing Laboratory on the same day for NO 3 --N and NH 4 + -N soil test. The experimental design is in randomized complete blocks with 4 repetitions. Experimental plots were 10-ft wide × 60-ft long.

Changes in NO 3 -N and NH 4 -N
The form of N in the soil was dependent on soil type (moisture and texture) and climate (temperature and precipitation) characteristics. In general, NH 4 -N content in the soil was greater at the initial corn growth stages and decreased during the season. Consequently, NO 3 -N content increases as a result of the nitrification process (Figure 1).
The use of NI contributed to maintain greater NH 4 -N content early in the season in the 0-12 in. depth but no changes in the 12-24 in. depth for any of the corn growth stages (Figure 2). However, the soil NO 3 -N content was greater for most sampling times in the 0-12 in. depth when the nitrification inhibitor was used. At the 12-24 in. depth, soil NO 3 -N content showed an increase at the V8 corn growth stage for the treatment without nitrification inhibitor. This increase matches with a peak observed at the same corn growth stage at the 0-12 in. soil layer suggesting a leaching process of NO 3 -N from the top to the deeper soil layer (Figure 2).
The increase of N fertilizer rates promotes a consequent increase in soil N. However, the NH 4 -N fraction was generally low with soil sampling during the growing season, suggesting a low sensitivity of the NH 4 -N fraction for soil sampling/testing (Figure 3). On the other hand soil NO 3 -N concentration was generally greater, and with significant differences with the use of nitrification inhibitor at the 200 lb N/a rate suggesting a reduction in the nitrification process in the soil at this point in the season (Figure 3).

Introduction
Potassium is an essential plant nutrient and is the third most common yield-limiting nutrient in agricultural production. The bioavailability (solubility) of soil-K is governed by equilibrium reactions between three main pools: nonexchangeable-K (K non ), exchangeable-K (K ex ), and soluble-K (K sol ). In many soils, the vast majority of total soil-K exists in the K non pool, where K is either trapped between clay platelets or fixed in the crystalline structures of various minerals (e.g. orthoclase and feldspars). Exchangeable-K is associated with cation exchange sites and may enter the soil solution via displacement from soil colloid surfaces. Soluble-K consists of K + ions in the soil solution, which is immediately available for plant uptake but is also the smallest soil-K pool. Even though K non is typically much larger than both K ex and K sol combined, the latter are of particular importance to agriculture, as they represent the bulk of soil-K available for plant uptake over a given growing season. As such, most soil tests for K target the K ex and K sol pools, and are used in combination with fertilizer response curves to make K fertilizer recommendations.
Several soil tests for K are currently employed by laboratories across the U.S.; however, ammonium acetate (NH 4 OAc) and Mehlich-3 (M3) are currently the most popular. The KSRE soil testing lab uses M3 for soil phosphorus, but continued using NH 4 OAc for soil tests for K. While there are some contrasting chemical characteristics between these two solutions (e.g. pH), the primary mechanisms for K extraction are similar in theory. Primarily this should occur through displacement of K + from the cation exchange complex by NH 4 + . As both solutions contain NH 4 + and have similar reaction times (shake times), the amount of K + extracted should be similar for a given soil. Researchers in other states have demonstrated a near 1:1 correlation between measurements made from these two procedures, however, data correlating the two methods have been limited in Kansas soils. The objectives of this study were to investigate the relationship between NH 4 OAc and M3 extractable K, and determine whether M3-K can directly replace NH 4 OAc-K in K fertilizer application rate calculations for crops grown in Kansas soils.

Laboratory Analysis
Soil samples were randomly selected from soils submitted to the KSRE soil testing lab by farmers and homeowners during 2016-2017 year. Each sample was dried at 40°C and ground to pass a #10 sieve (2 mm). Samples were measured into extraction vessels using 2 g standard soil scoops (NCR) and extracted according to the procedures described in the NCERA 013 Recommended Chemical Soil Test Procedures handbook. Briefly, extractions were performed using a 1:10 soil-extractant suspensions of either M3 (0.2 M CH 3 COOH, 0.25 M NH 4 NO 3 , 0.015 M NH 4 F, 0.013 M NHO 3 , 0.001 M EDTA; pH = 2.5 0.1) or NH 4 OAc (1.0 M NH 4 OAc; pH 7.0 0.1), with a reaction time of 5 minutes. Extracts were filtered using Ahlstrom 642 filter paper and analyzed using a PerkinElmer Aanalyst 200 Atomic Absorption Spectrometer. The relationship between Mehlich-3 and NH 4 OAc extractable K was investigated using linear regression procedures.

Results
A total of 776 samples from 46 different counties in Kansas were included in the study (Table 1). A strong positive correlation was observed between NH 4 OAc-K and M3-K over the entire data set (r = 0.99) ( Table 2), values for which ranged from 50 to 960 ppm and 41 to 991 ppm, respectively. The near 1:1 relationship ( Figure 1) and standard error of the linear regression model (0.97 and 0.005, respectively) suggest that M3-K values could be used as direct replacements of NH 4 OAc-K values when calculating fertilizer recommendations without recalibration. Table 1. General summary of samples used in the study, soils from 46 Kansas counties were used in the study, and covered a wide range of soil pH, Mehlich-3 K (M3K) and   Figure 1. A strong and positive correlation was observed between Mehlich-3 and NH 4 OAc extractable potassium (K) over a wide range of soil types and K concentration. The near 1:1 fit and strong fit of the model (slope = 0.97, R 2 = 0.98) suggest Mehlich-3 K may be a suitable replacement for NH 4 OAc-K in K fertilizer recommendations.

Introduction
Crop yields in acidic soils can be limited by several factors, namely reduced root growth and vigor caused by metal toxicity (e.g. aluminum (Al), iron (Fe), and manganese (Mn)), and reduced availability of essential plant nutrients. For example, the availability of phosphate (PO 4 3-) is highly dependent on pH, and precipitation of Al, Fe, and Mn phosphates is an important mechanism for reduced phosphorus (P) availability to plants grown in acidic soils. As such, neutralization of soil acidity is often necessary to maintain crop production and farm profitability.
Remediation of acid soils requires the neutralization of the total soil acidity, which can be conceptualized as two main pools, active acidity and reserve acidity. Active acidity is simply the hydrogen ions (H + ) in the soil solution and can be measured through soil pH measurements. Reserve acidity buffers the soil pH (active acidity) and requires some form of titration to measure, as it is caused by acidic cations (e.g. Al 3+ , Fe 3+ , and H + ) sorbed to the cation complex. Given the time-consuming nature of soil titrations, pH buffers are often used instead to quantify total soil acidity and to generate lime recommendations. In practice, both soil pH and buffer pH are used, where soil pH is used to determine if lime should be applied and the buffer pH is used to determine the amount of lime required to achieve the target pH.
Several different buffer solutions are used at labs across the U.S. Historically, the KSRE soil testing lab has used the Smith-McLean-Pratt (SMP) pH buffer. However, this solution contains hazardous chemicals, such as p-nitrophenol and chromium, and poses a risk to human health and the environment if not handled and disposed of carefully. Buffers without these hazardous chemicals have been developed in recent years, such as the Sikora buffer solution, and many soil testing labs are using them to reduce operating costs. The Sikora buffer solution was designed as a direct replacement for the SMP buffer. The goal of this study was to evaluate the correlation of the Sikora buffer solution with the SMP solution in Kansas soils and the potential to estimate reserve acidity and provide lime recommendations.

Experimental Procedures
Soil samples were randomly selected from across the state of Kansas. Samples were dried at 40°C overnight and ground to pass a #2 sieve (approximately 2 mm) using a flail type soil grinder. Samples were then analyzed for organic matter (OM), soil pH, SMP buffer pH, and Sikora buffer pH. Soil pH was measured from 1:1 soil-water suspensions. Organic matter was determined via the loss on ignition approach with a muffle furnace operating at 400°C. Both Sikora and SMP pH values were measured according to procedures recommended in North Central Regional Research Publication No. 221 (revised). Given the nature of random sampling, some samples were deemed inappropriate for use in the study. Soil samples with a soil pH > 6.4 or OM content > 10% were removed from the data set prior to analysis. The relationship between Sikora and SMP buffer pH values was investigated using Pearson's product-moment correlation and linear regression techniques.

Results
Soil pH ranged from 4.5-6.4 and soil OM from 0.8-9.2%, in the set of samples included in the study (279 samples). Sikora and SMP pH values ranged from 5.5-7.2 and 5.3-6.9, respectively, with a strong positive correlation (r = 0.9) (Figure 1). The strong correlation and linear nature of the relationship between Sikora and SMP suggests that Sikora could suitably replace SMP for lime recommendations in Kansas soils. However, since Sikora pH values were higher than SMP values, new equations should be used (Figure 2). buffer solution and Sikora buffer pH (r = 0.9). On average, Sikora pH values tend to be higher than those measured using SMP and corrections will need to be made to lime recommendation equations.

Introduction
The acidification of soil is a natural process where soil pH decreases over time. This process is accelerated by agricultural production with the use of N fertilizers and can affect both the surface and subsoil depending on the N fertilizer placement. Increasing the amounts of N fertilizer rates can accelerate the soil acidification process. As a consequence of low soil pH, an increase in soluble aluminum (Al) levels can affect root growth and therefore result in poor crop growth and production. Correction of the pH/Al problem by liming can allow for more efficient use of nutrients such as N and P, as well as water (Olsen et al., 2000). In the past, lime recommendations and lime application research have focused on thorough incorporation of the lime material to the soil. However, multiple years of surface applied N in no-tillage systems often lead to a decrease in soil pH near the surface, with a stratification of soil pH (Godsey and Lamond, 2001). The objective of this study was to evaluate crop response to surface lime applications under no-till with a stratified and low soil pH near the soil surface.

Procedures
Two field sites (A and B) were established in Mitchell County, KS and evaluated during 3 years (2016,2017,2018); exploring the effect of lime application in wheat (first year), corn (second year), and soybean (third year). Both sites were managed with no-till for more than 25 years. The lime used in the study had 87% of effective calcium carbonate (ECC) and it was not incorporated. The studies were set the fall of 2015 using 4 lime treatments: 1) control (no lime); 2) 0.5-ton/a ECC; 3) 1-ton/a ECC; and 4) 3-ton/a ECC. The experimental design was in randomized complete blocks with 4 replications. The experimental plots were 15-ft wide × 40-ft long. Initial soil tests before lime application are presented in Figure 1.

Wheat
After the first year, there was an increase in wheat yield up to 8% with lime application. At Site A, the lime application of 0.5-ton/a ECC resulted in an increase of wheat yield of about 5.9% (Figure 2A). At Site B, the 0.5 and 1.0 t/a rate showed a response of 8.1 and 7.8%, over the control respectively ( Figure 2B). Combined across the two locations there was a 5.3% yield increase to lime application in wheat. The magnitude of the response was small, however there was a consistent benefit in yield ( Figure 2C).

Corn
For corn (second year), liming showed yield response of up to 10% higher yields. Corn yields were increased at both sites ( Figure 3A and 3B). Considering the relative response of corn yield to lime application across the two locations there was an increase of 6% in yield ( Figure 3C).

Soybean
Soybean yield response to lime (third year) varied by site, with up to 17% yield increase at Site A, but variable response at Site B. (Figure 4). The relative response of soybean yield to lime application across the two sites showed an increase of 6.5% in yield ( Figure  4C).

Introduction
Nitrogen is an essential element for plant growth and reproduction. After it is applied as fertilizer on soil, N changes its chemical form, continually being subjected to critical processes of loss. Nitrification is an important step in the N cycle in soil promoted by the biological oxidation of ammonium to nitrite and nitrate. Conversion of this ammonium (NH 4 + -N) to nitrate (NO 3 --N) increases nitrogen leaching due to the mobility of NO 3 --N, and can be lost from the plant rooting zone . Nitrification proceeds rapidly in warm, moist, well-aerated soils.
Nitrification inhibitors are chemicals that slow down or delay the nitrification process, thereby decreasing the probability that large losses of nitrate will occur before the fertilizer nitrogen is taken up by plants . The objective of this study was to evaluate the response from the use of a nitrification inhibitor on corn grain yield.

Procedures
The study was carried out at four locations (Manhattan, Scandia, Rossville, and Ashland, KS) during 2017 and 2018 crop seasons. Treatments were: 1) N fertilizer without nitrification inhibitor (control), and 2) N fertilizer treated with nitrification inhibitor. Anhydrous ammonia was applied in four rates 0, 100, 150, and 200 lb/a. The experimental design was in randomized complete blocks with 4 repetitions. Experimental plots were 10-ft wide × 60-ft long. Chlorophyll meter measurements (SPAD) were taken at the V2, V4, V8, V12, and R1 corn growth stages. Soil samples were taken at the same growth stages at the soil depth of 0-24 inches and submitted on the same day to the K-State Research and Extension Soil Testing Laboratory for NO 3 --N and NH 4 + -N analysis. The two central rows of each plot were machine harvested. Grain weight was recorded and adjusted for 15.5 % moisture.

SPAD Measurements and the Relationship with NO 3 -N and NH 4 -N in the Soil
The SPAD measurements have high correlation with N content in the tissue (Ma et al., 1994). During the corn season there was a gradual increase in the SPAD values with a posterior decrease at the R1 growth stage. Similarly, soil NO 3 -N showed an increase during corn growing season in most sites, suggesting important contribution of this N form for corn N nutrition (Figure 1). Therefore, SPAD measurements showed higher correlation with soil NO 3 -N than soil NH 4 -N.

Corn Yield Response to N Fertilization and Nitrification Inhibitors
Nitrogen fertilizer application increased corn yield (N fertilizer vs. the check); however, corn response among N rates was not statically significant in this study (Figure 2). The optimum N rate across all locations was at 117 lb N/a ( Figure 2). Furthermore, no differences in corn yield were observed when anhydrous ammonia was treated with a nitrification inhibitor at the locations for this study (Figure 3). It is likely that N loss potential was low for these locations/years, resulting in no yield difference with the use of nitrification inhibitors.