Effect of Long-term Lantana Addition on Soil Phosphorus Fractions and their Relationship with Crop Yield and Phosphorus Uptake in Rice-Wheat Cropping in North West Himalayan Acid Alfisol

A long-term field experiment with rice-wheat cropping was started in wet season of 1988 with four levels of lantana (0, 10, 20 and 30 t ha⁻¹ on fresh weight basis) and three tillage practices (No puddling, puddling and soil compaction). From wet season of 1997, however, three tillage practices were replaced with three levels of N and K to rice (33, 66 and 100% of recommended) and 66% of recommended N, P and K to wheat. The P was totally omitted to rice crop. The recommended Nand K to rice were 90 and 40 kg ha⁻¹ whereas N, P and K to wheat were 120, 90 and 30 kg ha⁻¹. Lantana biomass was added to rice exactly 10–15 days before transplanting/puddling every year. Among P fractions, the highest increase was observed in NaHCO₃-Po (35–71%) followed by NaOH-Po (19–49%) and minimum in Res-P (8–17%) with twelve annual additions of lantana. The continuous twelve annual additions of lantana also increased available P by about 23–71% over no lantana addition. It was observed that among different P fractions NaHCO₃-Pi and NaHCO₃-Po were the most important P fractions contributing to nutrition of rice and wheat grown in a sequence. All the organic and inorganic fractions of P except Res-P and HCl-P were independent of one another.