| Farmland water use efficiency is an important indicator of sustainable agricultural development,and wheat-cotton double cropping can effectively improve farmland water use efficiency.Therefore,it is of great significance to analyze the spatial-temporal variation characteristics of soil moisture in the wheat-cotton two-cropping cotton field for the efficient use of water resources and precision irrigation in the cotton field.This paper was based on field trials of three cropping modes of wheat/relay intercropped cotton(WIC),wheat/direct-seeded cotton(WDC)and monoculture cotton(MC).The spatial grid method was used to sample and quantify soil moisture,and Geostatisic method is used for the Spatial-temporal heterogeneity analysis.By exploring the law of soil water movement and water consumption during the entire growth period of cotton,can provide a theoretical basis for the rational use of water resources and intelligent irrigation.The main results are as follows:1.The results showed that the soil moisture distribution had a certain spatial heterogeneity.According to the semi-variogram result partial abutment value/abutment value ratio found above 0.7,proved that the spatial distribution of soil moisture had a strong autocorrelation.According to the fitting of soil moisture,it was found that the coefficients of determination were all above 0.94,and the best fit of the spatial variability model of soil moisture was the Gaussian model.Before and after the cotton planting time,the semivariance function variation range of the three planting modes were all greater than the actual sampling interval of 20 cm,indicated that the research data can show the spatial variability of soil moisture.Among the three models,the direct seeding cotton had the shortest change range and the worst growth.The biomass accumulation and the soil water consumption were less.Therefore,soil water consumption was one of the important factors that determined the spatial difference.2.The effect of wheat-cotton double cropping on soil moisture content is mainly concentrated within 0-50 cm soil layer.During the flowering period,the soil moisture of WIC and WDC in the 0-50cm soil layer between the cotton rows was higher than MC,and the average values were 0.265 m~3/m~3and 0.26 m~3/m~3,and MC was only 0.19 m~3/m~3.However,after complete flocculation,the soil moisture of WIC and MC changed greatly,and the soil water contents were 0.24 m~3/m~3 and 0.22 m~3/m~3,respectively.The soil moisture change of WDC was small,and its value was 0.25 m~3/m~3.Among them,WDC and MC soil moisture changes are concentrated in the soil layer above 50 cm,and the deepest WIC can reach 70 cm.3.There were significant differences in cotton water consumption under different planting patterns.The cumulative soil water consumption was WIC>MC>WDC.The water consumption of WIC in 2017and 2018 was 254.13 and 278.65 mm,respectively.MC decreased 46.01 and 17.3 mm compared to WIC,and WDC decreased 50.03 and 34.96 mm compared to WIC.From the perspective of soil water consumption during the entire growth period of cotton,except for the wheat-cotton symbiosis period,the overall water consumption trend of WIC and MC tends to be consistent,and the highest values of soil water consumption occured between July and August.The total water consumption of WIC in the two months were 129.47 and 145.18 mm,respectively,and the highest could reach 12.08 and 12.28 mm in a single day,and the MC were 113.80 and 143.43 mm,respectively,and the highest were 10.8 and10.39 mm in a single day.The water consumption of WDC after entering the cotton growth period was lower than that of the other two models in the same growth period.The total water consumption in July and August were only 89.97 and 111.70 mm,and the maximum daily water consumption were only 7.74and 7.32 mm.4.MC’s cotton production and biomass are the highest,with lint production in 2017 and 2018being 1659.3 and 1258.8 kg/hm~2,respectively.Compared with MC,WIC’s two-year production decreased by 462.9 and 112.7 kg/hm~2,respectively,and WDC decreased 986.8 and 592.7 kg/hm~2.In2017 and 2018,the soil water use efficiency of WIC,WDC and MC were 4.71,4.50,7.97 kg/(hm~2·mm)and 4.11,3.21,4.82 kg/(hm~2·mm),respectively.Under the three planting modes,MC had higher yield and water use efficiency;but under the two-cropping mode,WIC had higher yield and water use efficiency than WDC. |
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