Effects of water and nitrogen reduction on content of carbon and nitrogen and activities of related enzymes in maize tillage layer under the shallow buried drip irrigation

The soil nutrients and biological characteristics are important indicators of soil quality. The study on effects of water and nitrogen reduction on content of carbon and nitrogen and activities of related enzyme in maize tillage layer under the shallow buried drip irrigation, which is of great significance for the sustainable production of maize and conservation of arable land in irrigation areas of the Xiliaohe plain. Based on two consecutive year field experiment, the conventional water-nitrogen treatment of traditional border irrigation (4000 m³·hm⁻² for border irrigation and 300 kg/hm² for nitrogen application) was used as the controlled trial, and the drip irrigation quota was used as the main treatment with three levels of drip irrigation volume of 40% (W1), 50% (W2), and 60% (W3) of the conventional irrigation volume, and nitrogen application as the sub-treatment with the conventional nitrogen application volume of 50% ( N1), 70% (N2) and 100% (N3), to explore the effects of water and nitrogen reduction on different forms of carbon and nitrogen contents and related enzyme activities in maize tillage layer under the shallow buried drip irrigation.The results showed that the different forms of carbon and nitrogen contents and related enzyme activities under shallow buried drip irrigation increased with the increase of irrigation quota and nitrogen application; the different forms of nitrogen content and soil enzyme activity under W3 were significantly higher than these under W2 and W1, soil nitrogen content W3 average increased by 13.2% and 6.4% compared with W2 and W1, and soil enzyme activity under W3 average increased by 8.5% and 16.9% compared with W2 and W1; the different forms of carbon content and soil enzyme activity under N3 and N2 did not differ significantly, soil carbon content under N3 and N2 average increased by 1.3% and 0.5% compared with N1, and soil enzyme activity under N3 and N2 average increased by 8.2% and 3.9% compared with N1. The soil quality index was highest in W3N3 and the differences with W3N2 and W2N3 were not significant, and W3N3, W3N2 and W2N3 respectively increased by 81.2%, 68.4% and 61.5% compared with CK annually. The soil quality index shows a significant positive correlation with the contents of different forms of carbon and nitrogen in the soil as well as the activities of related enzymes. Under shallow subsurface drip irrigation, the appropriate treatment of reducing water and nitrogen application can maintain a relatively high soil quality by increasing the contents of different forms of carbon and nitrogen nutrients in the soil and the activities of related enzymes. Combining the results of water-saving and weight loss, soil characteristics and quality evaluation, W3N2 under shallow drip irrigation with water and fertilizer integration, i.e., 30% nitrogen reduction and 40% water reduction, can maintain relatively good soil quality in the maize tillage layer.