Soil nutrient audits for China to estimate nutrient balances and output/input relationships

摘要

China has been able to feed a rapidly growing population by increasing crop yields, partly through the use of mineral fertilizers. Although now faced with a lower population growth rate, the prospects for increasing food production are uncertain because of the decline in the rate of increase in crop yields. This paper describes the use of a nutrient audit model to calculate nutrient output and input relationships, nutrient balances, and nutrient depletion rates between 1961 and 1997. Over the last two decades, China has been able to reduce its nitrogen (N) deficit through the use of large quantities of N fertilizers and has now achieved a balance. About 65% of total N inputs are supplied as N fertilizers. Significant progress has also been made in reducing the phosphorus (P) deficit from 1.2 million tonnes in 1985 to 0.6 million tonnes in 1997, when P fertilizer accounted for 57% of total P inputs. There is, however, a major annual depletion of potassium (K) which increased from 2.9 million tonnes in 1961 to 8.3 million tonnes in 1997. Potassium balances for the 30 provinces in China in 1996 indicate high depletion rates in all provinces. China has no large K reserves so most K fertilizers have to be imported. Application rates of K have remained relatively low and K fertilizer accounts for only 14% of total K inputs.