Abstract:

The aim of this research was to examine the impact of replacing chemical fertilizer with organic fertilizer at equivalent nitrogen levels， and the effects of varying intercropping ratios， on the forage yield and water use efficiency （WUE） within a silage maize/forage soybean intercropping system in the Loess Plateau region. The experiments were conducted in the tableland region （Xifeng） and the hilly gully region （Huanxian） of the Longdong Loess Plateau in 2024. Six treatments were established， as follows： 100% chemical nitrogen fertilizer with two rows of maize/two rows of soybean （M2S2F） and four rows of maize/two rows of soybean （M4S2F）； replacement of chemical fertilizer with organic fertilizer at an equivalent nitrogen level with two rows of maize/two rows of soybean （M2S2O） and four rows of maize/two rows of soybean （M4S2O）； and silage maize monoculture （M） and forage soybean monoculture （S）. We investigated the effects of these cropping patterns and organic fertilizer substitution on the system’s dry matter yield， crude protein yield， land equivalent ratio， interspecific competition coefficient， WUE， and economic benefits. The results show that substitution with organic fertilizer led to yield stabilization at both sites， while reducing the application rate of chemical fertilizers. At both sites， the dry matter yields of intercropping systems were in between those of the maize and soybean monocultures. Neither the planting pattern nor the substitution with organic fertilizer significantly affected the system’s crude protein yield. At Xifeng， intercropping systems with 100% chemical nitrogen fertilizers demonstrated several advantages， with forage soybean exhibiting stronger competitiveness than silage maize. All intercropping systems had higher WUE than the average values of monocultures. At Xifeng， M4S2F exhibited the optimal overall performance， with a dry matter yield of 25.9 t·ha^-1， crude protein yield of 2.86 t·ha^-1， and WUE based on dry matter yield of 90.49 kg·ha^-1·mm^-1， reflecting a 22.0% increase compared with monocultures. It also achieved a maximum net income of 24690 CNY·ha^-1. At Huanxian， the intercropping system consisting of two rows of maize/two rows of soybean exhibited higher land use benefits， with silage maize maintaining competitive dominance across all intercropping treatments. At Huanxian， M2S2O demonstrated the optimal overall performance， with a dry matter yield of 17.2 t·ha^-1， crude protein yield of 1.98 t·ha^-1， WUE based on dry matter yield of 57.63 kg·ha^-1·mm^-1， and net income of 16052 CNY·ha^-1. This reflected an 8.5% increase in WUE based on dry matter yield compared with monocultures. In conclusion， it is recommended to adopt 100% chemical fertilizer with a four rows of maize/two rows of soybean intercropping system in the tableland region of the Loess Plateau， and to replace chemical fertilizers with organic fertilizer at an equivalent nitrogen level and use a two rows of maize/two rows of soybean intercropping system in the hill-gully region of the Loess Plateau.

Key words: organic fertilizer substitution with equivalent nitrogen for chemical fertilizers, silage maize/forage soybean intercropping system, forage yield, water use efficiency