Effects of reducing potassium fertilizer on rice yield and potassium use efficiency under wheat straw return condition

There has been an increasing soil potassium deficiency in China. However, crop residues generally contain high level of potassium that could replace part of the potassium fertilizer requirements after returning straw to the soil, and can therefore alleviate soil potassium deficiency. Crop residue return to field is an effective way to reduce the use of potash fertilizer, which also improves potassium use efficiency. In this study, field experiments were carried out to determine rice yield potassium accumulation and partial factor productivity of potash fertilizer under conventional potash fertilizer application of 135 kg(K₂O)·hm^-2 (control) and reductions by 10%, 20%, 30% and 40% after wheat straw incorporation (6 000 kg·hm^-2). The potassium content and the quantity of accumulated potassium in rice reduced with decreasing potassium fertilizer application after straw incorporation into the soil. The yield, economic benefit, effective panicle number, grains per panicle and seed-setting rate of rice declined with the reduction of conventional potassium fertilizer rate from 10% to 40%. However, when potassium fertilizer was reduced by less than 30%, there was little impact on 1000-grain weight of rice. It also had no significant effect on yield or economic benefit of rice (P>0.05). Compared with conventional fertilization, treatments with chemical potash fertilizer reduction of 10%, 20%, 30% and 40% increased partial factor productivity of potassium fertilizer by 8.4%, 18.9%, 33.8% and 44.4%, respectively. In summary, potassium accumulation in rice plant, rice yield and economic benefit decreased, whereas partial productivity of potassium increased with the reduction of conventional potassium dose from 10% to 40%. When wheat straw was applied and conventional potassium fertilization dose reduced by less than 30%, partial factor productivity of potassium fertilizer increased but had no significant effect on the yield and economic benefit of rice.