Effect of different-sources and time of application of organic manures on residual fertility and nutrient balance in aerobic rice (Oryza sativa l.)

A field experiment was conducted during kharif 2009 at Zonal Agricultural Research Station, V. C. Farm, Mandya, University of Agricultural Sciences, Bengaluru. The initial status of available N, P₂O_s and K₂O of the experimental site was 248.5, 26.8 and 202.8 kg/ha, respectively. The variety used was Thanu (KMP-101). The results of the field experiment showed that different organic sources did not significantly influence the organic carbon content, pH and EC of soil after harvest of aerobic rice. Significantly higher amount of nitrogen (272.7 kg/ha), phosphorus (37.2 kg/ha) and potassium (211.6 kg/ha) found in soil after harvest of the crop was observed with FYM 10 t/ha as a basal dose+cattle urine at 100% N equivalent basis. Significantly lower amount of nitrogen (255.2 kg/ha) and phosphorus (29.8 kg/ha) in soil after harvest of the crop was observed with recommended dose of fertilizers (100: 50: 50 kg N; P: K/ha) alongwith 10 t of FYM/ha. The study revealed that balance of nitrogen was negative in all the treatments. The least balance of nitrogen was in the treatment (T₂: -44.2 kg/ha) followed by T₈: -42.7 kg/ha and T₄: -42.4 kg/ha. Available phosphorus balance was negative in all the treatments except in the vermicompost alongwith cattle urine applied treatment (2.41 kg/ha). The cattle urine applied treatments resulted in greater negative balance of potassium. The lower nutrient content of organic manures resulted in greater negative balance of phosphorus and potassium as compared to other treatments.