Yield quality and water and nitrogen use efficiency of guar beans under mulched drip irrigation in response to water and nitrogen interactions in arid areas

Guar is a typical legume cash crop native to India. Guar beans are ever-rising in the market share at present. Among them, the guar gum of its seed endosperm has been mainly used in the oil exploration industry. Water-based fracturing fluid can be formulated to increase the permeability of oil-bearing strata during oil production. In addition, guar gum is also widely used in paper making, textiles, food, spices, drugs, as well as mining and metallurgical industries. The nutrient-rich green seeds of guar beans are edible for food vegetables, due to a large amount of protein and a small amount of fat. The plant can be used as fodder and green manure. However, the low supply of guar gum on the market cannot fully meet the broad market space. Only a small number of planting areas of guar beans are suitable for the cultivation of guar beans in the food industry. Among them, Xinjiang located in the northwestern inland arid zone is very similar to the unique geographic conditions for the production and cultivation of guar beans. The temperature and heat conditions are suitable for the origin of guar, rich in the light and heat resources under the soil and water environment, with the high temperature difference between day and night, due to the scarce rainfall and high evaporation. But the relatively small region of guar bean planting still remains so far. Therefore a broad prospect can be expected to optimize the water and nitrogen management for the high crop yield and efficient use of water and nitrogen. This study aims to explore the water and nitrogen mode suitable for drip irrigation of guar beans under film in the Xinjiang area of China. Four irrigation levels were set: W1:1 170 m³/hm², W2:1 530 m³/hm², W3:1 890 m³/hm², W4:2 250 m³/hm²; Two levels of nitrogen application were: N1:30 kg/hm², N2:50 kg/hm². A systematic investigation was made to clarify the effects of water and nitrogen interaction on the growth index, yield, water, and nitrogen use efficiency, as well as the quality of guar bean during drip irrigation under film. The results showed that the coupling effect of water and nitrogen shared a significant effect on the yield, irrigation water use efficiency, and partial factor productivity of nitrogen fertilizer (W3>W4>W2>W1). There was an increase in the plant height, stem diameter, dry matter accumulation, yield, water use efficiency, galactomannan, soluble sugar, and polysaccharide content of Guar bean under the N2 level, compared with the N1 level. Only the partial productivity of nitrogen fertilizer decreased slightly. Principal component and membership function analysis showed that the optimal treatment was achieved in the irrigation amount of 1 890 m³/hm² and the nitrogen application rate of 50 kg/hm²(W3N2). The finding can also provide a theoretical basis to promote the yield, water, and nitrogen use efficiency of Guar bean under mulched drip irrigation.