Long‐Term Fertilizer Experiment Network in China: Crop Yields and Soil Nutrient Trends

Abstract

Results are summarized for the first 15 yr of an eight‐site, long‐term experimental network in China designed to assess the sustainability of cropping systems in environments representing 70% of Chinese cropland. Systems were wheat–maize double cropping (two crops per year) at four sites, wheat–rice double cropping, rice‐based triple cropping, and wheat or maize single cropping. Without fertilizers, wheat yields were mainly ≤1 t ha −1 , and maize yields were ≥2 t ha −1 With NPK fertilizer (rates averaging 154, 33, and 54 kg ha −1 per crop of N, P, and K, respectively), wheat yields mainly ranged from 5 to 7 t ha −1 , and maize yields ranged from 6 to 9 t ha −1 Without P fertilizer, yields declined (up to 4 t ha −1 less than with NPK), and Olsen‐P values in soil declined, although rates differed between sites. Decreasing yields from withholding K usually emerged more slowly. The results emphasize the value of long‐term experiments to reveal trends in soil fertility not apparent within a few years and the need for research in these environments to define “critical concentrations” of plant‐available P and K in soil for maintaining maximum crop yields. Results with manures show the risk of overfertilization and water pollution with N and P if inorganic fertilizer applications are not decreased to take account of nutrients from manure. At two sites, there was evidence of significant N and P inputs from irrigation water. At one site, the addition of N fertilizer gradually caused soil acidification; this caused inefficient utilization of nutrients and led to crop failure.