Species Interactions and Nitrogen Use during Early Intercropping of Intermediate Wheatgrass with a White Clover Service Crop

Shoujiao Li,Erik Steen Jensen,Linda-Maria Dimitrova Mårtensson,Yingjun Zhang,Nan Liu

doi:10.3390/agronomy11020388

Abstract

Perennial grain crops intercropped with legumes are expected to use nitrogen (N) resources efficiently. A pot experiment using the 15N isotope dilution method demonstrated interspecific competition and use of N from the soil and N2 fixation in intermediate wheatgrass (Thinopyrum intermedium (Host) Barkworth & D.R. Dewey, IWG) and white clover (Trifolium repens L., WC) intercrops at five species-relative frequencies and four levels of inorganic N fertilizer in a replacement series design. The proportion of N in WC derived from the atmosphere increased from 39.7% in a sole crop to 70.9% when intercropped with IWG, and 10.1% N in IWG transferred from WC. Intermediate wheatgrass showed high fitness with maintained high total dry matter production at low relative frequencies. Decreasing IWG-relative frequency only increased dry matter and N accumulation of WC, resulting in increased amounts of N2 fixed. Increased levels of N fertilization increased the proportion of N acquired from the fertilizer in IWG and WC but decreased the N fixed by WC and N absorbed by IWG from the soil. Our study indicates that WC supply sufficient fixed N2 for IWG intercrop biomass yields under appropriate levels of soil N fertility and species-relative frequencies.

Highlights

Agriculture is under increasing pressure to improve productivity while limiting negative environmental impacts under the circumstances of climate change and population growth
Our results suggest the improvement of dry matter yield and N content of intermediate wheatgrass (IWG) should not rely on overcrowding in sole cropping but the exploitation of complementarity and beneficial interactions between IWG and white clover (WC) intercrops
When we compared the N accumulation of IWG intercrops at N0 with N accumulation of IWG sole crops at N1, we found that despite the low species-relative frequency, the IWG intercrops achieved comparable N accumulation at N0 to the IWG sole crop (0.70 g pot−1) fertilized with 75 kg N ha−1, suggesting that the WC service crop can supply enough N for IWG under appropriate soil N fertility and species-relative frequencies

Summary

Introduction

Agriculture is under increasing pressure to improve productivity while limiting negative environmental impacts under the circumstances of climate change and population growth. The current global agriculture is dominated by the cultivation of annual crops, which may lead to many environmental problems, due to practices such as frequent tillage, reduced soil organic matter, and overuse of fertilizers and pesticides [1]. Perennial grain crops have been proposed by scientists to reduce these problems They have extensive root systems and several years of permanent ground cover, which could increase water and nutrient use efficiency, soil organic matter, carbon sequestration, soil faunal diversity, and decrease tillage, soil erosion, and energy consumption [2]. The intercropping of cereals and legume service crops has been approved to produce greater yields, improve nutrient use efficiency, improve soil fertility through biological N2 fixation, provide better lodging resistance, reduce pest incidence, improve forage quality, save synthetic fertilizer use, offering greater financial stability as compared to sole crops grown on the same amount of land [7,8]

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