Long term effect of organic amendments and mineral fertilizers on soil phosphorus and uptake in wheat

A field experiment was carried out to determine soil P status and P nutrition status of wheat in relation to long term use of organic amendments including farm yard manure (FYM), wheat straw (WS) and green manure (GM) and mineral fertilizers (NPK). Soil from the experimental site was a clay loam in texture, non-saline, calcareous, alkaline in reaction, low in organic matter and available P and adequate in exchangeable K. Soil analysis showed that application of organic amendments had highly beneficial effect in improving organic matter levels. On an average, the values increased from 0.83% to 0.89% with application of WS, to 1.05% with GM, and to a maximum of 1.40% with application of FYM. By comparison the effect of mineral fertilizers was negligible. Wheat yields increased significantly with the application of mineral fertilizers as well as organic amendments. But the response to mineral fertilizers was much more pronounced (656 to 4081 kg ha-1) than that due to organic amendments (2629 to 3139 kg ha-1). Maximum yield was achieved at the fertilizer rate of 120-90-0. While in case of organic amendments, the application of FYM and GM increased the yield of wheat significantly to 3129 and 2911 kg ha-1 respectively, while the application of WS had no influence on the yield of wheat. Olsen P content of soil ranged from 3.80 to 8.75 mg kg-1 for various treatments. The data regarding available P in soil indicated that Olsen P increased with increase in the rate of P applied (mineral fertilizers) and also due to organic amendments. It was further observed that the mean value for FYM plots (8.25 mg kg-1) was higher than that at the initiation of this study (7.38 mg kg-1) but the plots receiving other amendments showed considerable decline in Olsen P values. Thus the average values for other organic amendments were 4.95 mg kg-1 where no organic amendment was applied, and 5.84 and 5.48 mg kg-1 respectively where WS and GM amendments were applied. In case of mineral fertilizers, soil P status increased, on an average, from 5.35 to 6.54 mg kg-1 with application of recommended rate of NP. Phosphorus content of the flag leaf varied from 0.36 to 0.51 (%) for various treatments. The average values regarding organic amendments ranged from 0.43 to 0.46%. However, the effect of mineral fertilizer was more pronounced in comparison to organic amendments whereby P% increased from 0.39 to 0.49% with NP fertilization. In case of wheat grain, P content varied from 0.31% to 0.48% for various treatments. Averaged by organic amendments the values ranged from 0.39% to 0.42% for various organic amendments. This was not the case when NP fertilizers were applied which increased P% of grain significantly from 0.351% where no mineral fertilizer was applied to 0.443% for the treatment receiving recommended rate of NPK fertilizers. The data regarding total P uptake presented much better picture of the overall effect of organic amendments and mineral fertilizers. The response to these treatments is quite evident from the wide range in P update which varied from as low as 1.86 kg ha-1 to a maximum of 25.22 kg ha-1. Averaged by organic amendments, the value ranged from 12.78 kg ha-1 for unamended plots to 16.50 kg ha-1 for the plots receiving FYM amendment. In case of mineral fertilizers, the average values ranged from 2.75 kg ha-1 on unfertilized control plots a maximum of 21.89 kg ha-1 for the plots receiving recommended rate of NPK fertilizers. The results indicated that integrated use of organic amendments and mineral fertilizers significantly improved the grain yield and phosphorus nutrition of wheat. FYM application was particularly beneficial among the organic amendments while NP fertilization significantly increased soil P status as well as P content uptake in wheat.