Assessment of crop responses under varying levels of soil available nitrogen (N), phosphorus (P) and potassium (K) is important to develop site-specific nutrient management (SSNM) strategies. This study was conducted to investigate the spatial variability of soil N, P and K levels in paddy grown soils in Anuradhapura, Kurunegala and Polonnaruwa districts and corresponding yield response for nutrient application. Seventy-one paddy fields were selected and four plots (3×6 m) were established at each site comprised of a treatment applied with ample amount of N, P and K and corresponding omission treatments. At harvesting, total yield of each plot was recorded. Considerable heterogeneity of soil N (12.5-43.9 mg/kg), P (2.7-34.2 mg/kg) and K (14.6-221.9 mg/kg) was observed in paddy grown soils of the three districts. A significantly higher average yield of N applied treatment (5.8 Mg/ha) than that of N omitted treatment (3.9 Mg/ha) indicated a yield response for N application.However, nonsignificant differences of average yields of P (5.7 Mg/ha) and K (5.6 Mg/ha) omitted and ample treatments (5.8 Mg/ha) revealed a poor yield response for the application of these nutrients. Stepwise multiple regression analysis revealed that neither the initial soil P and K levels nor the other studied factors (growing season, irrigation scheme, soil texture, pH, EC, available Fe and Mg) have an impact on yield responses observed for P and K applications. Our results indicated large spatial heterogeneity in soil P and K levels in paddy grown soils. Absence of a significant response for the applied P and K and a considerable variability of yield responses highlighted the need of further studies on P and K reserves of paddy growing soils and factors controlling the variability in yield response. Further, site-specific application of N is shown as a priority to improve the productivity of paddy lands.
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