[Effects of intercropping on soil nitrification and nitrogen supply in potato field.]

Nitrate supply in soils is essential to meet nitrogen (N) demand of crops. However, how intercropping would affect soil nitrate supply and the underlying mechanisms remain unclear. Based on a field experiment of mono- and inter-cropped potato amended with four N application rates (N₀, 0 kg·hm^-2; N₁, 62.5 kg·hm^-2; N₂, 125 kg·hm^-2; N₃, 187.5 kg·hm^-2), we analyzed the differences in soil nitrate content and intensity, nitrification potential, and ammonia oxidation gene abundance. We further explored the mechanisms underlying the effects of intercropping on nitrate supply and N regulation. The results showed that both content and intensity of soil nitrate increased with N application rate. Under the same N level, nitrate content in intercropping soil was lower than that in monocropping soil. Nitrogen application increased soil nitrification potential, with stronger effects in monocropping than that of intercropping. The amoA gene abundance of AOB in soil was greater than that of AOA. The abundance of amoA gene for both AOA and AOB were increased firstly and then decreased with increasing N application rate when potato intercropped with maize. Under the same N application rate, AOA gene and AOB gene in all treatments (except N₂) in intercropping were lower than those in the monocropping. The amoA gene abundance of soil AOB and AOA decreased and nitrification potential was weakened when potato intercropped with maize, resulting in a decrease of soil nitrate content and intensity. Therefore, intercropping led to a reduction of soil nitrate supply, which was related to the microbial process of soil N transformation. Much attention should be paid to soil N supply under the condition of potato and maize intercropping.