Can interseeding leguminous cover crops inhibit silage maize growth and reduce water-nitrogen use efficiency in arid region?

Silage maize (Zea mays L.) is a prominent forage crop in arid regions where water scarcity and the need for optimized nitrogen (N) fertilizer use pose significant challenges to agricultural productivity and sustainability. Interseeding leguminous cover crops with silage maize can enhance sustainable soil development and improve N management through biological N fixation. However, the competition interactions between silage maize and cover crops under constrained water-N conditions remains uncertain. This study conducted a three-year field experiment of interseeding leguminous cover crops with silage maize under varying drip fertigation conditions. The treatments included three types of leguminous cover crops-red clover (TP, Trifolium pretense L.), common vetch (VS, Vicia sativa L.), and hairy vetch (VV, Vicia villosa Roth)-combined with two N application rates (N1: 120 kg N ha⁻¹ and N2: 180 kg N ha⁻¹ and two irrigation levels (W1: 75 % of ET_c and W2: 100 % ET_c). The results showed that interseeding did not significantly inhabit plant height, stem diameter, and relative leaf chlorophyll content of silage maize compared to no covers (P>0.05). Under identical water and N conditions, the hay yield of maize interseeded with VV was significantly higher by 15.3 %-21.9 % compared to no covers (P<0.05), and the hay yield of the interseeding system vetch was significantly higher by 22.7 %-28.4 % (P<0.05). Specifically, under VV, W2N1 decreased actual evapotranspiration (ET_a) by 2.1 %-12.9 % (P >0.05), and increased water use efficiency (WUE) by 8.6 %-12.5 % (P>0.05) and nitrogen partial factor productivity (PFPN) by 24.1 %-43.3 % (P<0.05) compared to W2N2. Dry matter of cover crops, which contributed to the increases in PFPN and WUE, ranged from 0.8 to1.2 Mg ha⁻¹. Structural equation modeling indicated that the N application was the most important influencing the interseeding system. In conclusion, a 100 % ET_c irrigation amount and a 120 kg N ha⁻¹ N application rate in a silage maize-hairy vetch interseeding system can effectively increase forage yield and enhance water and N utilization efficiencies in the arid region.