Utilization of phosphate rocks as a source of phosphorus for sugarcane production on acid soils in south China

Acid red soils are widely distributed in South China and characterized by low pH, low fertility and, in particular, low phosphorus (P) availability. In order to test the effectiveness of direct application of phosphate rocks (PRs), three PRs from North Carolina, Morocco, and China and one local triple superphosphate (hereinafter abbreviated as NCPR, MORPR, CHNPR, and TSP, respectively) were applied to sugarcane grown on lateritic red soils. The experiments were conducted at two sugarcane plantations located in Qianjin State Farm and Dongfanghong State Farm of Guangdong Province, People's Republic of China, from 1991 to 1994. Each phosphate was applied at three rates (125, 250, 500 P2O5 kg/ha) as basal fertilizer in the first year. In the first year at the Qianjin site, TSP increased cane yield significantly with increasing rates of application, while NCPR and MORPR also increased yield significantly at or above the rate of 250 kg P2O5/ha. In the second year, TSP still increased the yield but without difference among application rates, and NCPR and MORPR showed positive effects on yield at the highest rate. In the third year, TSP, NCPR, and MORPR increased the yield at the highest rate. However, CHNPR did not show any positive effect on sugarcane yield in three consecutive years. At the Dongfanghong site, TSP, NCPR, and MORPR increased cane yield significantly at and above 250 kg P2O5/ha in the first year. In the second and third years, TSP, NCPR, and MORPR showed positive effects on cane yield at all rates. As for CHNPR, it increased yield at all rates in the second year but only at 500 kg P2O5/ha in the third year. Sugar concentration was not influenced by phosphate sources and rates in the three consecutive years at both sites. Comparing the four phosphates, we found that TSP had the best effect on sugarcane growth in the first year, while NCPR and MORPR showed similar effect on yield to TSP in the second and third year, but CHNPR did not result in any sustainable and satisfactory effect on sugarcane growth. The differences in effectiveness of phosphate sources on sugarcane growth may be explained by differences in the reactivity of the tested fertilizers and soil and climatic conditions in different sites. It is suggested that PRs with high reactivity could not only be effective for the first crop but also have good residual effects and hence could be a feasible alternative to available phosphate fertilizers that are extensively used in local sugarcane production.