How Nitrification Inhibitors Perform in Kansas

Nitrogen fertilizers are used extensively to increase crop yields. Crops often recover less than 50 percent of the applied nitrogen during the year of fertilizer application. The lower nitrogen recoveries can stem from the loss o f nitrate nitrogen from the soil by leaching and denitrification. Most nitrogen fertili zers contain ammonium or ammonium-forming types of nitrogen. In the soi l, ammonium nitrogen generally is adsorbed onto clay and organic matter where it resists leaching and denitrificat ion. However, at soi l temperatures above 50° F, ammonium nitrogen is converted to nitrate nitrogen by a two-step process called nitrification. The ammonium nitrogen is first converted (oxidized) by Nitrosomonas bacteria to nitrite which is relatively unstable in soil and is rapidly converted by Nitrobacter bacteria to nitrate nitrogen. Nitrate nitrogen is not adsorbed by t he soil but remains dissolved in the soil solution where it moves freely with the flow of water and is taken up

Nitrogen fertilizers are used extensively to increase crop yields.Crops often recover less than 50 percent of the applied nitrogen during the year of fertilizer application.The lower nitrogen recoveries can stem from the l oss o f nitrate nitrogen from the soil by leaching and denitrification.
Most nitrogen fertili zers contain ammonium or ammonium-forming types of nitrogen.In the soi l, ammonium nitrogen generally is adsorbed onto clay and organic matter where it resists leaching and denitrificat ion.However, at soi l temperatures above 50° F, ammonium nitrogen is converted to nitrate nitrogen by a two-step process called nitrification.The ammonium nitrogen is first converted (oxidized) by Nitrosomonas bacteria to nitrite which is relatively unstable in soil and is rapidly converted by Nitrobacter bacteria to nitrate nitrogen.
Nitrate nitrogen is not adsorbed by t he soil but remains dissolved in the soil solution where it moves freely with the flow of w ater and is taken up by plant roots.Too much moisture from rain or irrigation c auses water to move below a crop's root zone and carry some nitrate with it.Nitrate moved below the root zone is considered to be lost by leaching.Nitrate also may be lost by denitrific ation, especially under extremely waterlogge d conditions.
The percentage of the nitrogen f e rtilizer used by crops can be increased by reduc ing nitrogen losses.One method is to apply nitrogen when the crop needs it -by sidedressin g or through irrigation (fertigation ).Another met hod to reduce losses would be to apply an ammoniac al form of nitrogen and maintain it in this form as long as possible or until the plant uses it.This latter method could be accomplis hed by incorporat ing a nitrificatio n in- hibitor with the ammoniac al f ertilizer to delay the nitrifi cation process (s low conversion to nitrate).
Nitrificatio n inhibitors prevent or retard the first step of nitrificatio n of ammoniac al nitrogen by the Nitrosomo nas bacteria.The only product now available for this use is nit rapyrin, 2-chloro-6-(trichloro-Me thyl) pyridine (N-SERVE) .Other produ cts, such as etradiazol e (DWELL), are currently being studied for labeling as nitrificatio n inhibitors.

RESULTS OF KANSAS RESEARCH
Our research on Eudora sandy loam soil at t he Kansas River V alley Experimen t Field, Rossville, showed that N-SERVE inhibits nitrificatio n, so that anhydrous ammonia remains in the ammoniac al form longer into the growing season (Table 1 ).A higher ammonium nitrogen level was maintained in the soil up to the tassel stage of growth (6-29-78 and 7-12-79) both years.Results in 1979 at the Sandyland Experim ent Field, St. John, on a Pratt loamy fine sand and at the North Central Experimen t Field, Scandia, on a Crete silty loam were similar.
Field evaluation on corn, wheat and grain sorghum have been conducted in Kansas with N-SERVE from 1975 through 1979 and wit h DWELL from 1977 through 1979.The five-year results (Table 2) show more sites with no respo nse than sites with increases.Although we occasiona lly included N-SERVE and DWELL in the same study, they are listed as separate sites for each inhibitor.

CORN
Corn, which uses more nitrogen than whea t or sorghum, has been most responsive to nitrificatio n inhibitors.All corn-yield increases attributab le to  3).Even on coarse soils, yield responses (from 9-22 bu/a, Table 4) were obt ained less t han half t he time -probably because weather co nditions were not conducive to leac hing some years.However, of the twelve sites listed as not responsive, three of nine N-SERVE sites and one of three LL sites on coarse textured soils showed a t r end, though not statistically significant, of 7, 10, 16, and 9 bushels increase per acre, respectively .In most cases, increased y iel ds correlated with higher nitrogen uptake by plants.Higher phosphorus uptakes also were observed at some sites.N-SERVE and DWELL usually performed sim ilarly at sites where both were evaluated.1 0 a Three of nine N-SE RVE sites and one of three DWELL sites with no statistically significant y ield response had increases of 7, 10, 16, and 9 bushels per acre, respectively.bThree of five N-SERVE sites and t he DWELL site with no statistica lly significant yield response had decreases of 5, 4, 7, and 15 bushels per acre, respectively.
DWELL decreased yields on silt loam at the Tribu ne Branch Experiment Station by 16 bushels per acre in 1978.The same trend, although not significant, was also observed with DWELL in 1979 (15 bushels decrease per acre) and with N-SERVE in 1979N-SERVE in , 1978N-SERVE in and 1976 (5, 4 (5, 4, and 7 bushels decrease per acre, respectively).We have no logical explanati on for these yield decreases due to nitrification inhibitors on this silt loam soil.
This publication from Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived.Current information: http://www.ksre.ksu.edu.

WHEAT
Nitrification inhibitors have had rel atively little effect on wheat yields in Kansas (Table 5).One significant yield increase w as observed with DWELL on a sandy soil in 1979, but only at one nitrogen rate and one inhibitor rate.Excessively wet conditions favoring nitrogen l osses were considered responsible for the 5.6 bushel increase per acre with N-SERVE at the Osage County silty clay loam site in 1978 (Table 6).Two yield decreases of 7.3 and 2.2 bushels per acre were observed at the Sandyland Experiment Field in 1976 and 1978, respectively .Recent research indicates that applying N-SE RVE before planting winter wheat lets muc h of it degrade before spring, so it would be less effective in reducing spring nitrogen losses.
Yield increases from placing nitrogen in the same band as phosphorus fertilizer is tho ught to be a result of N-SERVE maintaining the nitrogen in the ammoniacal form for a longer period of time, thu s having a greater effect on phosphorus uptake than without N-SERVE.However, an additional yield advantage with N-SERVE has not been observed at every location where dual plac ement has resu lted in increased yields.

GRAIN SORGHUM
As shown in Table 2, only three of the nineteen sites showed an increase in sorghum yield with N-SE RVE or DWELL.N-SE RVE gave a fo ur bushel per acre increase at the Colby Branch Station in 1976 and 24 bushels per acre at the Sandyland Experiment Field (coarse soil) in 1977.An 11 bushel per acre increase was obtained with DWELL at the Sandyland Experiment Field in 1977.Most of t he sorghum studies have been on medium to fine textured soils.

SUGGESTIONS FOR USE
Research has shown that.under excessive rainfall, maintaining applied nitrogen in the ammoniaca l form could benefit c rops on sandy soils subject to leaching losses of nitrate nitrogen and possibly on fine t extured or claypan soils sub ject to denitrification.
Corn grown on coarse text ured soil is more responsive to nitrific ation inhibitors than corn on fine textured soil.Present recommendatio ns for corn on coarse textured soil include sidedressing ni-  4. Yie lds of corn at sites responsive toN-SERVE and DWELL in Kan.sas, 1975-1979.Corn yield, bu/a @1 5.5% of the sorghum studies w ere on silt loam soils not usually susceptible to nitrogen losses, so a nitrification inhibitor might be warranted in some cases.If the past history of a fie ld ind icates losses of applied nitrogen in years of excess ive moisture, a nitrification inhibitor might be a good investment.

Table 1 .
This publication from Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived.Current information: http://www.ksre.ksu.edu.Soil ammonium levels after application of anhydrous ammon ia on a Eudora sandy loam,Rossville, 1978 and  1979.

Table 2 .
Effects of N-SERVE and DWELL o n yields of corn, wheat and grain sorghum on all soil types inKansas, 1975Kansas,  -1979.   .
This publication from Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived.Current information: http://www.ksre.ksu.edu.

Table 5 .
Effect of N-SERV E and DWELL on wheat y ields inKansas, 1975-1979.Wheat and grain sorghum have shown l ittle response t o nitrifi cation inhibitors.However, m any ' One study area with N-SERVE and DWELL as separate t reatments.2At 75 lb N/a only.