Abstract
Sustainable intensification of pulses needs reduced input of nitrogen (N) fertilizer with enhanced crop nutritional quality and yield. Therefore, increasing N harvest in grains (sink organs) by improving N remobilization is of key importance. Previous research has shown that a lower dose of N fertilizer effectively increases the rate of N remobilization, while intercropping improves the grain N concentration in pea (Pisum sativum L.). However, it is unknown whether intercropping can facilitate this N fertilizer effect to increase N remobilization, and thereby enhance the N harvest index (NHI). In this study, we determined N allocation among different organs of pea plants, N translocation from leaf and stem tissues to pods, N2 fixation, N utilization efficiency, and NHI of pea plants grown alone or intercropped with maize (Zea mays L.) with different N fertilization treatments in a field experiment in northwestern China from 2012 to 2014. A base application of 90 kg N ha−1 at sowing and top-dress application of 45 kg N ha−1 at flowering integrated with maize–pea intercropping increased N allocation to pod tissues, N translocation to grains, and NHI of pea plants. Compared with the application of 90 kg N ha−1 at sowing and 135 kg N ha−1 top-dressed at flowering, reducing the top-dress application of N fertilizer to 45 kg N ha−1 increased N allocation to intercropped pea plants by 8%. Similarly, N translocation to grains from leaf and stem tissues was increased by 37.9 and 43.2%, respectively, enhancing the NHI by 40.1%. A positive correlation between N2 fixation and NHI was observed, implying that N2 fixation improves N concentration in grain sinks. Thus, our data show that growing pulses in an intercropping system with reduced N fertilization are essential for maximizing N translocation, improving nutritional quality, and preventing the loss of N through leaching, thereby avoiding potential groundwater contamination.
Highlights
Nitrogen (N) is a vital element for adequate crop growth and the production of grains, and supplemental N fertilizer is often required to optimize crop yield (IFA, 2009; Kaur et al, 2017)
A significant positive correlation of NTR for stem (P = 0.027) and NTC for leaf (P < 0.001) and stem (P < 0.001) was observed with Na-t (Table 5). These findings indicate that N translocation from vegetative organs to grains is vital for the final N accumulation in pea; this final N accumulation is more closely associated with N translocation from stem than from leaf
In Denmark, reducing the rate of N fertilization by 50% along with wheat– pea intercropping has been shown to increase N yield and grain N concentration; sole-cropping of wheat and pea with 80 kg N ha−1 increases N input, resulting in negative environmental impact (Ghaley et al, 2005). Consistent with these studies, our results showed that pea–maize intercropping increased N concentration in pea grains compared with sole cropping and traditional N fertilizer application
Summary
Nitrogen (N) is a vital element for adequate crop growth and the production of grains, and supplemental N fertilizer is often required to optimize crop yield (IFA, 2009; Kaur et al, 2017). To maintain crop yield while reducing environmental risks, it is necessary to improve the N use efficiency of crop plants and reduce N input (Brooker et al, 2016) To achieve these goals, it is important to enhance the remobilization efficiency of N in crops (Schjoerring et al, 1995; Masclaux-Daubresse et al, 2010). Studies have shown that N deficiency, an abiotic stress, triggers earlier, and more rapid remobilization of N (Schjoerring et al, 1995; Mu et al, 2016) This contributes to higher grain protein content and seed nutritional quality (Samonte et al, 2006; Klimek-Kopyra et al, 2018a). Grain protein content is negatively correlated with yield; it is important to identify approaches that increase N harvest index (NHI) while maintaining yield (Masclaux-Daubresse et al, 2010)
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