Effect of phosphorus, potassium and lime application on pasture in acid soil in Yunnan Province in China

Provision of winter and early forage is a major problem for ruminant production in Yunnan Province, China. Temperate legumes (e.g. white clover) combined with perennial grasses (e.g. perennial ryegrass, cocksfoot) have potential to fill this feed gap for livestock production when high fertiliser inputs are maintained. In commercial practice, however, these legume/grass pastures perform poorly and lack persistence due to poor fertiliser management. This paper describes a low-input fertiliser strategy developed to maintain productive pastures on moderately acid (pH=5.3) Hapludult (red earth) soils in Sunming County, Yunnan. Since initial soil tests showed major deficiencies of phosphorus (<6 mg kg-1 Bray P) and K (16 mg kg-1) a replicated (3) experiment was done that included four rates of fused calcium magnesium phosphate (CaMgP) fertiliser (0, 500, 1000 and 1500 kg ha-1yr-1), four rates of potassium sulphate (K2SO4) fertiliser (0, 100, 200 and 300 kg ha-1yr-1) and four rates of quick (or burnt) lime (0, 500, 1000 and 1500 kg ha-1yr-1) to define a low-input P, K and Ca strategy for white clover/cocksfoot/perennial ryegrass pasture. Our results indicated that the lowest P rate (117 kg P ha-1 applied over 3 years) when combined with adequate K and Ca inputs produced 86% of the white clover production and 96% of the cocksfoot production measured at the highest P rate. K had only a small effect of pasture production when applied without P, but had a significant effect on the yield of white clover when combined with P fertiliser. Lime had no effect on either pasture production or the levels of available soil P and K, but it did raise soil pH >6.5. K deficiency was more serious for white clover than the grasses, and an annual application of ~50 kg K ha-1 was needed to retain white clover as a stable pasture component on these soils. We conclude from our results that it is technically feasible to make introduce temperate pastures on acid soils in Zhongdian Countprofitable through an annual application of a modest fertiliser rate comprising 500 kg ha-1 of fused CaMgP and 100 kg ha-1 of sulphate of potassium to overcome nutrient deficiencies. Due to the complexity of acid soil problems, we recommend a three-step process for successful pasture management: (1) undertake soil tests to identify the specific soil properties and nutrient deficiencies that are likely to limit pasture productivity; (2) choose pasture combinations that correctly match the right pasture species with existing soil constraint; and (3) tailor fertiliser strategies to specifically meet the nutrient requirements of the chosen pasture combination. Using this approach we recommend that only low inputs of P and K be applied and that perennial ryegrass be deleted from the temperate pasture species combination recommended for moderately acid soils in Malong County.