Fate of Nitrogen-15 fertilizer in Soil Plant system as Influenced by Nitrification Inhibitor

Abstract

A series of field experiments were carried out the farmers’ field in Mardan SCARP area (NWFP) to investigate the influence of nitrification inhibitor (N-serve) on wheat and maize at same experimental site. The effect of split application of N fertilizer was also evaluated and compared with the inhibitor effect on yield and N content of wheat and maize at same experimental site. The effects of inhibitor and the split application of N fertilizer on yields and N contents of wheat and maize were compared. The effectiveness of N-serve on nitrification inhibition was also evaluated in the field at several occasions i.e., 2, 5, 8, 16, 38 and 66 days after application. It was found that the N-serve was effective in controlling nitrification as the concentration NO3-N in soil was smaller in the inhibitor than in the no-inhibitor treatment at all occasions. The yield and N content of wheat increased significantly with N levels and the addition of inhibitor. On the average, the N fertilizer increased the grain yield by 2 t, DM by 4 t, and crop N by 55 kg ha-1. Similarly, the inhibitor increased the grain yield by 0.3 t, DM by 1.4 t, crop N by 22 kg ha-1 and crop recovery of applied N by 27%. The effect of inhibitor however varied with the level of N addition. The inhibitor was generally more effective at the low level of N addition. The research showed that the effectiveness of N fertilizer for wheat grown on the silty clay loam soil in NWFP can be markedly improved by using nitrification inhibitor. In the split experiment, the yield and N content of wheat increased gradually with increasing levels of N addition. Although the grain yield was increased by the split application, the differences between split and no-split treatments were not significant. The DM yield was increased significantly by the split treatment, the effect varying with the level of N-addition. The total crop N and the recovery of applied N by wheat plants increased by the split treatment, the differences between the split and no-split treatments however were not significant. By comparing the effect of nitrification inhibitor with the split application of fertilizer N on the yield and N content of wheat, the grain yield and shoot biomass of wheat were greater in the inhibitor than in the split treatment, the differences however varying with the level of N addition. The differences in yield between the inhibitor and split treatments decreased with increasing N rates. The N concentration, the total N uptake, and the recovery of applied N by wheat plants were significantly greater in the inhibitor than in the split treatment at all levels of N. It was, however, observed that the differences in N content of wheat between inhibitor and split treatments decreased with increasing levels of N application. These results indicated that the inhibitor treatment was relatively better than the split application of N fertilizer in terms of increased yield and N content of wheat. The soil analysis for NH4-N and NO3-N at 0-30 and 30-60 cm after wheat harvest showed that nitrification inhibitor controlled the leaching losses of NO3 The inhibitor eliminated the nitrification process which resulted into increased concentration of NH4-N in the surface layer (0-30 cm). Where the nitrification process was not eliminated (meaning inhibitor was not used), the concentration of NO3-N increased with depth (30-60 cm) which was a clear sign of downward movement of NO3-N from the surface in the absence of inhibitor treatment. The 15N-enriched experiment further revealed that all the yield and yield components (except 1000-grain weight) of wheat were substantially greater in the inhibitor than the no-inhibitor treatment. Similarly, the N uptake and % recovery of applied N by wheat crop were substantially enhanced by the use of nitrification inhibitor. Out of 1.5 kg N-N applied to wheat in the beginning of the experiment, 1.0116 kg was recovered by wheat crop in the inhibitor treatment with only 0.6605 kg ha-1 in the no-inhibitor treatment. IT was found that the % recovery of applied N-N in the inhibitor treatment was 67.44% compared with 44.03% in the no-inhibitor treatment. In order to assess the residual effect of nitrification inhibitor applied to wheat in November 1993 and to compare that with the split application of N fertilizer on the following maize crop, maize was planted on some treatment plots the next season (summer 1994). Unfortunately, the maize crop failed to germinate properly because of excessive and frequent rainfall during the sowing period. As a result, the maize population was sparse and un-uniform. The data obtained on the said crop was not reliable therefore did not present in this report. The residual effect of nitrification inhibitor was assessed and compared that with the split application of N fertilizer on the following wheat crop (1994-95). Results indicated that the inhibitor had the residual effect on the subsequent crop even after one year of its application. Both the grain and DM yields of wheat were significantly greater in the inhibitor than in the no-inhibitor treatment. Although N concentration in wheat grain and straw was not affected, the inhibitor treatment substantially increased the total accumulated N in wheat grain and straw compared with the no-inhibitor treatment. The total accumulated N and % recovery of applied N in wheat crop was also greater in the inhibitor than in the no-inhibitor treatment indicating the residual effect of nitrapyrin applied to previous wheat. The split application of N fertilizer increased the grain and DM yields of wheat but did not affect the 1000 grain weight and N concentration in wheat grain and straw. The total accumulated N in wheat grain and straw was considerably increased by the split application of N fertilizer. Similarly, the total N content and % recovery of applied N in wheat crop were substantially increased by the split treatment compared with no-split treatment. By comparing the residual effect of nitrification inhibitor with the split application on wheat crop, it was found that the grain and DM yields of wheat were greater in the split than in the respective inhibitor treatment. However, the differences in N concentration in grain and straw, total crop N and % recovery of applied N in wheat crop were not significant between the inhibitor and split treatment. The results obtained on soil analysis for NH4-N and NO3-N at different depths after wheat harvest (1994-95) showed that the concentration of NH4-N in the surface soil was persistently greater in the inhibitor than in the no-inhibitor treatment while that NO3-N greater in the latter than in the former treatment. Similarly, the concentration of NO3-N in the lower depth (30-60 cm) was greater in the no-inhibitor than in the inhibitor treatment. These results indicated that nitrapyrin had the residual effect on the residual effect on the mineral N status of the soil even after two years of its application. The residual effect of nitrification inhibitor was further assessed and compared with that of the spit application of N fertilizer on the following maize crop (2995). The results showed that the inhibitor was no more effective in enhancing the crop and N yield of maize as the differences in grain and DN yield, N concentration in grain and stover, total accumulated N and % recovery of applied N in maize crop were not significant between the inhibitor and no-inhibitor treatment. The split application of N fertilizer increased the crop and N yield of maize compared with the no-split treatment. By comparing the residual effect of nitrification inhibitor with the split application of N fertilizer on maize, it was found that the split application yielded significantly greater than the inhibitor treatment. This indicated that the effect of nitrapyrin disappeared completely after two and a half year of its application. This was further confirmed by the soil analysis for NH4-N and NO3-N at 0-30 and 30-60 cm where the differences in NH4-N and NO3-N concentration were not significant between the inhibitor and no-inhibitor treatments.