Influence of soil banding moisture uniformity on growth and water use efficiency of drip irrigated cotton under mulch

Abstract: In the design of drip irrigation under mulch, it is usually concerned with the point source or line source wetting uniformity of drip irrigation. However, because of the wide soil wetting area controlled by drip tape, the soil wetting uniformity is needed not only along the crop row, but also between the rows, so that the crops grow uniformly between the lines. Therefore, the proper design of the soil banding wetting uniformity under mulch can regulate cotton roots growth in the row, which plays a key role in improving the yield and water use efficiency, and is also unique design requirement of mulch drip irrigation technology in Xinjiang arid region. This problem should be paid more attention. To verify the importance of soil banding wetting uniformity under mulch drip irrigation technology, an experiment was carried out with 3 treatments, i.e. dripper flow of 1.69 (W169), 3.46 (W346) and 6.33 L/h (W633), respectively, to study uniformity influences on soil matrix potential, plant height, leaf area, root growth, cotton seed yield and water use efficiency of cotton rows. The results showed that the banding uniformity under mulch has a great influence on growth, water consumption and yield of cotton planted in each row, resulting in obvious differences of water use efficiency among cotton lines. As the wetting area of soil is transited from narrow-deep type (W169) to wide-shallow type (W633), the soil matric potential decreased more and the water stress of the cotton root became smaller, the uniformity of the soil moist under mulch turned higher, and the root distribution and plant growth of cotton were more uniform in the row. The differences of average cotton leaf area and average plant height between the inside and border rows under mulch were respectively 143 cm2 and 7.04 cm in narrow-deep type soil wetting area. The root length density, the theoretical and the practical yield difference values of seed cotton were respectively 386.3 m/m3、976 and 509.3 kg/hm2, and their water use efficiency were respectively 7.2 and 14.8 kg/(mm·hm2). The differences of average cotton leaf area and average plant height between the inside and border rows under mulch were respectively 9 cm2 and 3.74 cm in wide-shallow type soil wetting area. The root length density, the theoretical and the practical yield difference values of inside and border row under film in wide-shallow type soil wetting area were respectively 142.01 m/m3, 171 and 190.6 kg/hm2, and their water use efficiency were respectively 9.2 and 11.0 kg/(mm·hm2). The results proved that the cotton yield could be significantly improved under wide-shallow soil wetting area, and the water use efficiency would not decrease. Thus, the soil banding wetting uniformity should be focused in the design of drip irrigation under mulch when the standard and design method of drip irrigation were issued. We should not only consider the linear wetting uniformity of single row crops, but also consider the problem of soil wetting uniformity in the whole mulch width. And it's the basis to confirm the spacing between drip tapes.