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.

Long-term experiments for sustainable nutrient management in China. A review

“…Data from 10 long-term monitoring field sites indicated that soil pH decreased by 0.45 to 2.20 (Guo et al, 2010). Significant soil acidification has been found to drastically decrease crop yield in several treatments of a long-term experiment conducted in Hunan Province, China (Zhao et al, 2010). However, the correction would theoretically require 1.5 to 2.5 tons of CaCO 3 ha −1 yr −1 to counteract the acidity generated in the intensive cropping systems receiving high rates of N fertilizer application, and ten times this amount for greenhouse vegetable systems, which is a daunting task (Guo et al, 2010).…”

“…Sufficient evidence indicates that the combined application of NPK fertilizers and organic fertilizers (NPK+OF) can generally achieve higher crop yields than any of them applied alone (Poulton, 1995;Greenland, 1997;Manna et al, 2007;Hati et al, 2007;Bhattacharyya et al, 2008;Xu et al, 2008;Pan et al, 2009;Zhang et al, 2009a, b, c;Diacono and Montemurro, 2010;Zhao et al, 2010). A long-term field experiment from 1973 to 2004 conducted in India indicated a significant downward trend in yield of soybean for both the control treatment and the NPK treatment compared with a statistically significant upward trend with time for the NPK + FYM treatment (Bhattacharyya et al, 2008).…”

“…Based on the above review, it is fair to conclude that combination of organic and inorganic fertilizers is a better practice than applying organic or inorganic fertilizers alone, although Zhao et al (2010) made a good point by pointing out the fact that the manure + NPK treatment often had the highest inputs of nutrients and the highest yield should be expected. They called for better design of experiments to test different rates of inorganic fertilizers with and without manure to clarify unique contributions of manure that cannot be reproduced by using additional inorganic fertilizers.…”

“…Therefore, a recoupling of livestock and crop production is definitely needed, both on a local and regional scale. Another challenge is the difficulty of accurately predicting nutrient mineralization from different types of manures in different cropping environments, leading to either over-or under-application of inorganic fertilizers (Zhao et al, 2010).…”

“…Large year-to-year variability in crop yield has also been observed in long-term experiments in China (Zhao et al, 2010) and in-season N management strategies based on soil N min tests have been evaluated (Cui et al, 2008a, b). Recently, Li et al (2009) compared two in-season N management strategies for winter wheat in the NCP: one uses a soil N min test to determine soil N supply at the F6 stage, and then estimates the N topdressing rate; another strategy uses an optical canopy sensor to estimate crop N demand before topdressing, and then determines the N application rate following Raun et al (2002).…”