Study On Salt Transfer Laws Of Cotton With Drip Irrigation Under Plastic Mulch And Growth Index Of Cotton In Responses To Salinity

Cotton production developed fast because of the application of drip irrigation under plastic mulch in Xinjiang, then Xinjiang became the primary cotton production area. But the new secondary salinization problem had brought out with the increase of drip period. This problem had affected the application of drip irrigation under plastic mulch and the sustained development of Xinjiang agriculture. It was quite beneficial to study the salt transfer laws and establish early warning value. Then we could solve the secondary salinization problem and promote the Xinjiang agriculture.This test practised in Xinhu Farm of Agriculture Division No.6 of Xinjiang Production and Construction Group in 2007 and 2008. Salt Transfer laws for the cotton with drip irrigation under mulch were researched by choosing the land of different soil texture and different drip period, measuring soil salinity at different soil profile and each growth period in Xinjiang. Effect early warning value at different growth period was researched by choosing seven cotton fields with drip irrigation under plastic mulch with the salinity gradient and measuring the index at different growth period in Xinjiang. It would support the development of drip irrigation under mulch. The primary conclusions were listed as follows:1. Salt Transfer was different with the different soil texture. Salinity changed according to the characteristic of "salt moving with the water" with the growth period for loamy soil. Salinity was accumulated strongly at open ground of bare land and the depth of 60cm in the soil. Salinity changed slowly in clay soil and accumulated strongly below the depth of 80cm in the soil.2. The longer the drip period, the more the accumulation of salt in cotton field. The speed of salinity accumulation with increase of drip period in loamy soil was faster than that in clay soil. The salinity of drip 6 years was increased 75.93% in loamy soil, and 23.01% in clay soil. The biggest extent change of salinity accumulation was between drip 3 years and 4 years, from 0.71dS·m^-1 to 0.90dS·m^-1. We should irrigate completely every three years for stopping the secondary salinization in loamy soil. Salinity accumulated slowly in clay soil, and changed from 0.65dS·m^-1 to 0.80dS·m^-1 in 6 years.3. Salt distributions changed due to the effect among capillary force, soil matric potential and gravity in cotton field. It was a curve of"s"with the addition of soil depth at the uprightness, increased firstly and then decreased. The change extent in loamy soil was bigger than clay soil. Soil salinity above 60cm soil depth in loamy soil in drip 3 years at the level: emitter<the center of plastic mulch<bare land, below 60cm soil depth: emitter>the center of plastic mulch>bare land. Soil salinity in loamy soil over drip 3 years: emitter<the center of plastic mulch<bare land. It was approximate in clay soil with loamy soil above 40cm soil depth, the regularity was poor below 40cm soil depth.4. The result showed that salinity resistance of cotton became strong with the growth period. The soil salinity should be controlled below the light warning line during different growth period, it was below 0.99dS·m^-1 at bud stage, below 2.18dS·m^-1 at blossoming and boll forming stage, below 2.80dS·m^-1 at boll opening stage. The soil salinity below 0.6dS·m^-1 would not harm to the growth of cotton during every growth period. 5. Soil salinity had different influence to the factors, influence grade: bolls>plant number>boll weight. Bolls and plant number decreased significantly with the increase of soil salinity when soil salinity was above 0.95dS·m^-1, cotton yield was decreased highly significant. The yield reduction was due to the decrease of available bolls, but not reduction of single boll weight, therefore it should be increased bolls to achieve the hight yield of cotton in salinization soil.