Effect Of Irrigation Quota And Straw Buried Depth On Soil Hydrothermal And Saline Environment And Cotton Growth Under Aerated Infitrating Irrigation

In order to explore the effects of irrigation rate and straw return depth on soil structure,soil hydrothermal and saline environment and cotton growth in cotton fields in South Xinjiang under the aerated infiltration mode,three irrigation rates were set in this paper,(three irrigation gradients from low to high according to crop water demand coefficient and ET0)272mm(W1),310mm(W2),348mm(W3)and three straw return depth treatments of 15cm(D1),25cm(D2)and 35cm(D3).The response of soil structure,soil water,heat and salt transport,and cotton growth characteristics to irrigation quotas and straw return depth were observed and analysed under the aerated infiltration model,with the following main findings:(1)Irrigation rate and straw return depth had a significant effect on soil structure under the aerated infiltration irrigation mode.Under the same conditions of straw return depth,increasing the irrigation rate increased the water-stable macroaggregate content,mean weight diameter(MWD)and geometric mean diameter(GWD),effectively reducing the soil bulk,thereby increasing the soil porosity and optimising the three-phase composition of the soil.Under the high irrigation quota(W3)treatment,the MWD and GWD values were greater in the D2 treatment than in the D1 and D3 treatments.Under the same irrigation quota,soil bulk density tended to decrease and then increase with increasing depth of straw return,with D1 and D3 treatments increasing by 1.49% and 2.93% respectively compared to D2 treatment;soil porosity tended to increase and then decrease with increasing depth of straw return,with D1 and D3 treatments increasing by1.19% and 2.98% respectively compared to D2 treatment.Under the W3 irrigation condition,the D2 treatment reduced the percentage of solid phase and increased the proportion of gas-liquid phase compared with the D1 and D3 treatments,which improved the soil structure index.(2)The irrigation rate and the depth of straw return in the aerated percolation mode had a significant effect on the spatial and temporal distribution of hydrothermal salts in the soil.It was found that the straw compartment prevented the upward evaporation of water and salts to a certain extent,causing salt and water to accumulate at the straw,and when the irrigation rate was the same,the straw return depth of 15 cm had a better water retention effect on the soil as a whole,inhibiting the evaporation of water around the soakaway.When irrigation rates were the same,a straw return depth of 35 cm kept salt below the 35 cm straw compartment,inhibiting the upward migration of salt from the lower layers and making desalination in the root zone better than the other two return depth treatments.The straw return treatment can increase soil temperature,with a straw return depth of 25 cm and a straw return depth of 35 cm increasing the soil temperature at the corresponding depths respectively.(3)The irrigation rate and straw return depth had a significant effect on cotton growth and physiology in the aerated percolation mode.Cotton was strongly influenced by the irrigation rate,with cotton plant height,stem thickness and leaf area all showing a significant increase with increasing irrigation rate.At the same irrigation rate,cotton plant height,stem thickness and leaf area were greater in the D2 treatment than in the D1 and D3 treatments.Increasing the irrigation rate significantly increased leaf SPAD values,chlorophyll content and leaf photosynthetic characteristics under the same irrigation depth.Under the same conditions of irrigation rate,the SPAD value,chlorophyll content and leaf photosynthetic characteristics of D2 treatment were greater than those of D1 and D3 treatments.The average diameter,root volume,root length density,root mass density,root-to-crown ratio and seed yield per cotton plant were maximised at the W3 irrigation rate.The average root diameter,root volume and average root length density of cotton were significantly greater in the D2 and D3 treatments than in the D1 treatment under the W3 irrigation quota.Under the W3 irrigation rate,the root weight of D3 treatment was significantly greater than that of D2 and D1 treatments,respectively,and the root to crown ratio of D3 treatment was significantly higher than that of D2 and D1 treatments under the W1 irrigation rate.Under the same irrigation rate,the straw return depth of D2 treatment was higher than D1 and D3 treatments in terms of seed cotton yield per plant.