| The North China Plain is an important producing area of grain,cotton and oil in China.However,due to the shortage of fresh water resources,the agricultural irrigation has depended on the exploitation of deep fresh groundwater for a long term in the North China Plain,which has seriously impacted the sustainable utilization of water resources and stable development of agriculture in this region.Nevertheless,the shallow saline groundwater resources are abundant and widely distributed in the North China Plain,where the Heilonggang region is a typical area.The exploitation and utilization of saline water resources have great potential to alleviate the freshwater crisis.The saline water irrigation has persistent impact on soil environment and crop growth,however,the effect of long-term saline water irrigation on soil water,salt and crop yield in this region is still unclear.Based on a long-term located experiment on saline water irrigation of cotton(started in 2006),six levels of irrigation water salinity(1,2,4,6,8,and 10g/L)were set up in this study.Our study focused on the changes in soil water-salt in the 15 th year(2020)under saline water irrigation,the responses of cotton growth,yield and fiber quality,and water consumption characteristics,and combining with the comprehensive analysis of multi-year(2006-2020)data of soil salinity and cotton yield,to determine an appropriate border irrigation water salinity threshold for cotton in Heilonggang area of the North China Plain.Results showed that:(1)Soil moisture and salinity during cotton growth period showed an increasing trend with the increasing salinity of irrigation water.Compared with freshwater treatment,the average soil moisture within 0?100 cm of 2,4,6,8 and 10 g/L treatments increased by-1.96%,1.76%,2.75%,10.63% and 17.82%,respectively;soil salinity increased by 16.58%,60.30%,122.21%,215.95% and 319.88%,respectively.The fluctuation range of soil moisture and salinity increased with the irrigation water salinity increasing while decreased with the increase of soil depth.Compared with bare rows of cotton field,the soil moisture and salinity at cotton harvest had trends of increase and decrease in mulched rows,respectively;the average soil salinity within 0?100 cm decreased by 0.46% to 19.52% compared with that at sowing stage.From2006 to 2020,the soil salinity of each treatment did not accumulate linearly with the extension of irrigation years,but showed a large trend of fluctuation;a dynamic balance of soil salt within root zone of cotton could be maintained under treatments with salinity ≤ 4 g/L.(2)Irrigation with low salinity had no obvious negative effects on cotton seedling emergence and growth indicators(plant height,stem diameter,leaf area index(LAI),branch number and dry matter mass),while high irrigation salinity(≥ 6 g/L)dramatically reduced cotton seedling emergence rates,and inhibited cotton growth.The cotton growth indicators were significantly quadratically correlated with soil salinity,and the sensitivity to salinity was in an order of LAI > plant height > dry matter weight > branch number > stem diameter.(3)The saline water irrigation had less effect on reproductive organs than vegetative organs,tending to promote dry matter transport to the reproductive organs.With an increase in the irrigation water salinity,the number of pre-summer boll and summer boll tended to decrease,while the number of autumn boll tended to increase.Compared with 1 g/L treatment,the seed cotton yield under 2 and 4 g/L treatments was raised by 4.47% and 2.02%,respectively,while that of 6,8 and 10 g/L treatments decreased by 5.69%,17.25% and 27.97%,respectively.There was no significant difference in seed cotton yield among treatments with salinity ≤ 6 g/L.From2007 to 2020,the seed cotton yield showed dramatical inter-annual fluctuation,with no significant decrease existing under treatments with salinity ≤6 g/L in most years.Saline water irrigation had little effect on the upper half mean length,micronaire value,elongation rate,specific breaking strength and uniformity index of the cotton fiber,with the effect on micronaire value and elongation relatively greater.(4)The total water consumption of cotton exhibited a trend of first increasing and then decreasing under saline water irrigation;compared with 1 g/L treatment,the total water consumption under 2 and 4 g/L treatments increased by 2.05% and 0.21%,respectively,while that of 6,8 and 10 g/L treatments decreased by 3.99%,6.41% and 8.39%,respectively.With increasing salinity of irrigation water,cotton water use efficiency(WUE)first increased and then decreased.Compared with 1 g/L treatment,the WUE under 2 and 4 g/L treatments increased by 2.37% and 1.80%,while that of 6,8 and 10 g/L treatments decreased by 1.77%,11.58% and 21.37%,respectively.When the irrigation salinity was ≥8 g/L,the total water consumption and WUE of cotton decreased significantly in comparision with that under freshwater treatment.(5)Considering changes in soil salinity,cotton growth performances and yield responses over years,it was suggested that irrigation water salinity should not be higher than 4 g/L in the Heilonggang region of the North China Plain,under the condition that a dynamic balance of soil salt within cotton root zone could be maintained,the growth of cotton was not significantly inhibited,and the decline of multi-year yields of cotton was controlled below 5%. |
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