Effect of different modes of fertilizer application on soil potassium balance and rice yield

Based on fourteen years field experiment,the effect of mineral fertilizer and organic nutrient recycling(C) on soil K balance and rice yield was studied in the double-rice-cropping region of subtropical China.The results show that zero-fertilizer or only mineral fertilizer application makes the soil deficient in K.NP treatment shows grievous deficit with average K shortage of 120.1kg/hm².Combined application of organic manure and NP or NPK reduces negative K balance effect and even results in an increased soil K release.For instance,treatment NP+C has a negative K balance of 2.2kg/hm² deficit per year,and treatment NPK+C has a positive K balance of 154.5kg/hm² surplus per year.However,exorbitant K input can lead to a great deal of K nutrient loss,which reduces K use efficiency and increases risk of environmental pollution.In comparison with mineral fertilizer,organic nutrient recycling improves rice yield significantly.But the rate of production increase by recycling decreases with increasing proportion of N,P and K.Based on zero-fertilizer rice production-increasing rate of organic nutrient recycling is 56%,and incorporation with organic nutrient recycling,NP and NPK yield production-increasing rates are 18.8% and 10.2%,respectively.Treatments NPK+C₂ and NPK have no significant difference in rice yield.It is obvious that organic nutrient recycling can substitute chemical potassium fertilizer.Organic nutrient recycling decreases internal potassium use efficiency by the given sequence:NPK+C＜NP+C＜NPK＜NPK+C₂＜C＜CK＜NP.