Study on nutrient requirements of phosphorus and potassium of a legumina (Centrosema pubescens) grown in Humid Subtropical Areas of Yunnan

Experiments of applying phosphorus (P) and potassium (K) using randomized complete block designs with six treatments and four replications were carried out to investigate the nutrient requirements of a tropical legume-- Centrosema pubescens grown on the latosolic red earth in humid subtropical areas of Yunnan province. Thus, the objective was to obtain successful establishment and sustainable high yield of excellent tropical legumes, resolve the shortage issue of high quality forage and increase the output of stock raised in the areas. The results showed that dry matter(DM) yield, the total uptake of nitrogen, phosphorus, potassium and yield of crude protein of Centrosema pubescens per hectare significantly increased with P and K fertilizer application, especially a significant increase of yield was obtained through K fertilizer application. There was a significant positive relationship between P application rate and DM yield (Yp＝1289+50.5X-0.55X2, r=0.9519**) and yield of crude protein of Centrosema pubescens (Ycp＝254+12.2X1-0.14X12，r＝0.9398**), phosphorus fertilizer application can increase P content and decrease K content with the growth of Centrosema pubescens. Meanwhile, there was a significant non-linear positive relationship between K rate and DM yield (Yk＝1259+19.2X-0.087X2, r=0.8546**) and yield of crude protein of Centrosema pubescens.(Ycp＝248+4.3X1-0.0204X12, r=0.8055**), and K fertilizer application can increase K content of Centrosema pubescens. Based on analyses of plant and soil samples, it is concluded that P and K fertilizers should be applied at a ratio of 1:0.5-1.2 after Centrosema pubescens plant was established in the third year to maintain and stabilize high DM yield and quality of Centrosema pubescens.