EFFECTIVE NITRIFICATION INHIBITORS MAY IMPROVE FERTILIZER RECOVERY INIRRIGATED COTTON

N fertilizer is often poorly recovered in irrigated cotton production, due to N loss through denitrification. We researched the ability of i nhibitors to delay nitrification and reduce the availability of NO; to denitrifying microorganisms and thus improve N fertilizer recovery. 2 -Ethynylpyridine, etridiazole, and nitrapyrin proved highly effective nitrification inhibitors, although nitrification was evident several w eeks after their application. CaC2 was relatively ineffective, even wh en wax-coated to prolong the evolution of C2H2. Phenylacetylene and et hynylcyclohexanol were also ineffective, despite having a chemical str ucture similar to 2-ethynylpyridine. A strong association was identifi ed between each compound's ability to inhibit nitrification and its ca pacity to improve N fertilizer recovery. In one experiment, N fertiliz er recovery was increased by similar to 50% with 2-ethynylpyridine, et ridiazole, or nitrapyrin application, from 33% without inhibitors. The inhibitors had little effect on fertilizer recovery where N losses we re relatively small. 3-Methyl pyrazole significantly increased N uptak e and lint yield, but the nitrification inhibitors had no significant effect on N uptake or on yield in two of the three of the cotton crops . A laboratory study confirmed that nitrification inhibitor effectiven ess declined in the order 2-ethynylpyridine>etridiazole>nitrapyrin>3-m ethyl pyrazole>phenylacetylene>CaC2>ethynylcyclohexanol.