Impact of Cover Crops and Phosphorus Fertilizer Management on Impact of Cover Crops and Phosphorus Fertilizer Management on Nutrient Cycling in No-Tillage Corn-Soybean Rotation Nutrient Cycling in No-Tillage Corn-Soybean Rotation

Summary The objective of this study was to quantify the effects of cover crops and different fertilizer management techniques on the amount of nutrients being removed and recycled in the soil system. This study was conducted at Ashland Bottoms, KS, from 2014-2016. A 2 × 3 factorial design with three replicates was utilized in this study. The fertilizer management treatments included a control of 0 lb/a P 2 O 5 , along with fall broadcast and spring injected applications of P 2 O 5 based on a build and maintain recommendation system. Results show that total uptake of K 2 O and recycling of P 2 O 5 and K 2 O are directly influenced by cover cropping. Application of P 2 O 5 fertilizer also statistically impacted the yield of soybeans during the 2016 growing season.


Introduction
This study began in 2014 to determine the effect of cover cropping and fertilizer management on phosphorus (P) loss from a no-tillage corn-soybean rotation. By studying the effects of cover cropping and fertilizer management, this study looks to protect soil and water resources all while maximizing net returns and management flexibility for the producer. As part of this study, crop yield, nutrient uptake, and nutrient removal was determined.

Procedures
This trial was conducted at the Kansas Agricultural Watershed (KAW) Field Research Facility, located at Ashland Bottoms Research Farm in Manhattan, KS, on a Smolan silty clay loam with an average slope of 6-8%. The KAW research facility consists of 18 plots varying from 1.2 to 1.6 acres in size. Six different management systems are expressed in this study. These systems include fall broadcast (FB) application of phosphorus fertilizer, spring injected (SI) phosphorus fertilizer, and no phosphorus (CN) fertilizer. All fertilizer application methods were studied both with cover crop (CC), and no cover crop (NC). Treatments for this study were arranged in a 2 × 3 factorial design and replicated three times using randomized complete block orientation.
For the 2015 growing season, a cover crop mix of winter wheat, rapeseed, and hairy vetch was planted in November 2014 on all cover crop treatments followed by corn planting in April of 2015 for the entire experiment. Cover crop was terminated by herbicide at the time of corn planting. The FB plots received 75 lb P 2 O 5 /a as diammonium phosphate (DAP) broadcast in January 2015 and the SI plots received 75 lb P 2 O 5 /a as ammonium polyphosphate (APP), applied in a 2 × 2 placement at seeding. All applications of phosphorus fertilizer were based on build and maintain recommendations. Nitrogen (N) fertilizer was injected as 28% urea ammonium nitrate at various rates to each treatment to bring the total applied nitrogen up to 130 lb N/a per treatment. Corn ears were hand harvested from two 30-ft-long rows at three sub-plot locations. Care was taken to leave the corn husk attached to the stalk. Biomass samples were collected by harvesting ten stalks from each sub-plot location.
For the 2016 growing season, a winter wheat cover crop was planted in September of 2015 and terminated with herbicide in May 2016. Soybean was planted in June of 2016. The FB plots received 55 lb P 2 O 5 /a as DAP broadcast in November 2015 and the SI plots received 55 lb P 2 O 5 /a APP, applied in a 2 × 2 placement at seeding. Fertilizer applications rates were based on build and maintain recommendations. Biomass samples were collected from 3 feet of the planted row at three sub-plot locations. Grain was harvested from two rows across the entirety of each plot using a plot combine.
Three composite soil samples were collected at 0 to 2 and 2 to 6 inches deep from each plot following grain harvest but prior to fertilizer application each year of the experiment and analyzed for pH, P, potassium (K), nitrate (NO 3 -N), and organic matter. Soil analysis for 0 to 6 inches was computed as the weighted average from the 0 to 2 and 2 to 6 inch data.

Results
Cover crop and fertilizer treatments did not affect soil organic matter, soil pH, potassium, or nitrate concentrations in the soil (P > 0.05), therefore, these data were summarized by year (Table 1). The FB fertilizer increased the 0-to 2-inch soil test P each year ( Figure 1). The SI treatment maintained or increased soil test P, while the CN decreased soil test P ( Figure 1).
Analysis of cover crop nutrient uptake data revealed no statistical differences between fertilizer management practices for either year (Table 2). There was greater nutrient uptake in 2016 compared to 2015, which can be attributed to variance in growth between the two years. In 2015, cover crop growth was minimal due to cover crop being planted after soybean and being harvested prior to planting corn. There was much greater growth and therefore greater nutrient uptake during 2016.
Neither cover crop nor fertilizer management influenced corn growth, yield, or nutrient uptake in 2015 (P > 0.05; Table 3). The only effect of cover crop on soybean yield and nutrient uptake was decreased N content in soybean residue (Table 4). This could be caused by N uptake by the cover crop, but more data are required to be conclusive. Phosphorus fertilizer application increased soybean grain yield, total P uptake, and N, P, and K removal in the grain (Table 4). Greater N removal by P-fertilized soybean can be attributed to greater grain yield. Greater P and K removal by P-fertilized soybean is because of both greater yield and greater nutrient concentrations in the seed (data not shown).
In Table 5, the total nutrient uptake and removal for the 2015 and 2016 growing seasons are analyzed. Statistical differences were found in the total amount of K 2 O uptake along with P 2 O 5 and K 2 O returned to the soil in the residue for the CC versus NC plots. Plots grown with CC had statistically greater uptake of all three categories which is correlated to the CC plots having greater amounts of P 2 O 5 and K 2 O deposited on the surface with the plant residue. Statistical differences were also observed when comparing fertilizer management interactions. The FB and SI plots had statistically greater removal of K 2 O in the grain. This increased K 2 O content of the grain could be a result of heathier or greater root mass caused by the application of phosphorus fertilizer.      CC  160  15800  172  76  156  113  53  32  8250  58  23  123  NC  162  15400  175  72  153  117  52  32  7700  58  20 CC  547  152  407  346  98  112  193  53  290  NC  561  139  372  347  96  109  214  43