Effects of reduced nitrogen inputs on crop yield and nitrogen use efficiency in a long-term maize-soybean relay strip intercropping system.

Ping Chen,Li Zhou,Xiaoming Liu,Qing Du,Jiang Liu,Lu Lei,Junbo Du,Feng Yang,Kai Shu,Xiaochun Wang,Sajad Hussain,Taiwen Yong,Chun Song,Weiguo Liu,Wenyu Yang,Wen-Xiong Lin

doi:10.1371/journal.pone.0184503

Abstract

The blind pursuit of high yields via increased fertilizer inputs increases the environmental costs. Relay intercropping has advantages for yield, but a strategy for N management is urgently required to decrease N inputs without yield loss in maize-soybean relay intercropping systems (IMS). Experiments were conducted with three levels of N and three planting patterns, and dry matter accumulation, nitrogen uptake, nitrogen use efficiency (NUE), competition ratio (CR), system productivity index (SPI), land equivalent ratio (LER), and crop root distribution were investigated. Our results showed that the CR of soybean was greater than 1, and that the change in root distribution in space and time resulted in an interspecific facilitation in IMS. The maximum yield of maize under monoculture maize (MM) occurred with conventional nitrogen (CN), whereas under IMS, the maximum yield occurred with reduced nitrogen (RN). The yield of monoculture soybean (MS) and of soybean in IMS both reached a maximum under RN. The LER of IMS varied from 1.85 to 2.36, and the SPI peaked under RN. Additionally, the NUE of IMS increased by 103.7% under RN compared with that under CN. In conclusion, the separation of the root ecological niche contributed to a positive interspecific facilitation, which increased the land productivity. Thus, maize-soybean relay intercropping with reduced N input provides a very useful approach to increase land productivity and avert environmental pollution.

Highlights

With the continuous increase in the global population, food security problems are increasing, in China and India with 37% of the world population [1]
The competition ratio of soybean relative to maize (CRSM) increased with the increase in N input, and the ratio in all treatments was greater than 1 in 2012, suggesting interspecific facilitation
With the increase in years of planting, the interspecific facilitation converted to interspecific competition in the NN treatment, interspecific facilitation was retained under reduced nitrogen (RN) and conventional nitrogen (CN), which suggested that N input was required to achieve interspecific facilitation in long-term maize-soybean relay intercropping

Summary

Introduction

With the continuous increase in the global population, food security problems are increasing, in China and India with 37% of the world population [1]. In China, food production has greatly improved with the increased application of chemical N fertilizer. Maintaining crop yield with reduced N input in maize-soybean intercropping sustainable agricultural is attracting increased interest due to the depletion of fossil fuels and problems with food security. Produced N fertilizer increases the environmental costs of agricultural production and environmental pollution [2]. The abuse of N fertilizer further increases the environmental cost and decreases N use efficiency [3]. The inputs of chemical N fertilizer can be reduced by breeding N efficient cultivars, optimizing N nutrient management and choosing a suitable cropping system [4,5,6]

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Discussion

Conclusion