Effectiveness of phosphorus application in improving regional soybean yields under drought stress: A multivariate regression tree analysis

Scarcity of water often reduces the regional production of soybean (Glycine max (L.) Merr.) in many areas where it is grown. Contemporary climate change is characterized by increase in frequency and intensity of drought, yet little is known about the successful strategies of soybean cropping systems to drought stress at the regional scale. An effective way to improve the understanding is how to reduce the yields variability across regional fields and consequently increase total soybean production under drought conditions. In this study, using a series of household surveys and on-field trials conducted during a severe drought in 2007 provided data for 118 soybean fields throughout Hailun County of Northeast China, the triggers of regional yield variability and the relative importance of the determining factors were investigated. Regression trees analysis showed that regional soybean yield variability was mainly induced by soil available phosphorus and the amount of P applied, which explained 16.3 and 15.2% of the yield variation, respectively. Under drought stress, regional yields improvement could be accessed by altering P application rates. The productivity of soybean over the region did not increase when P application rate reached a threshold of 55.67 kg/ha. The results suggest that investing more P fertilizer was an effective management strategy for improving regional soybean production in Northeast China in such drought years and the level of effectiveness varied with the application rates.