NITROGEN-BALANCE AND N RECOVERY AFTER 22 YEARS OF MAIZE-WHEAT-COWPEA CROPPING IN A LONG-TERM EXPERIMENT

The influence of N, P and K application through inorganic and organic fertilizers on N recovery in crop plants and its balance in the soil-p lant (maize-wheat-cowpea fodder) was studied for the first 22 years of a long-term experiment at Punjab Agricultural University farm, Ludhia na, India. The results showed. that N removal and apparent N recovery by both maize and wheat was directly related to the balanced applicati on of N, P and K fertilizers. Averaged over the years, application of N alone (100% N) resulted in a recovery of 17.1% in maize and 31.7% in wheat. The application of P and K along with N almost doubled (32.8% in maize and 64.7% in wheat) the apparent N recovery in the crops. Inc rease in soil N concentration which was related to the build-up of soi l organic carbon (OC) occurred at a very slow rate with the applicatio n of N, P and K fertilizers. Addition of farm yard manure (FYM) result ed in highest N removal in crops and build-up of soil N and OC status. Application of recommended N without P and K fertilizers resulted in relatively large amounts (64-71%) of fertilizer N lost from the surfac e soil as compared to that (41-49%) with N, P and K applied together. Higher rate of fertilizer application (150% NPK) resulted in comparati vely greater N loss (58-62%). It was concluded that balanced and judic ious use of N, P and K fertilizers coupled with the addition of any de ficient element (e.g. Zn) help in minimizing N losses and environmenta l pollution.