Zinc Availbility Of Xinjiang Calcareous Soil And Response Of Cotton On Zinc Fertilizer

Xinjiang, which is located in the center of the Eurasian Continent, is an arid area. Thetotal zinc content of the soil is significantly higher than the average contents of China and theworld, but the available zinc content is limited. The soil available zinc content,0.5mg·kg^-1,was set as the critical index of zinc to calcareous soil crops in Xinjiang when the secondnational general survey of soil was conducted. This index has been in use for over30years.However, with the fast development of agricultural productivity, especially in cottonproduction in Xinjiang, soil nutritional status, and cotton varieties of Xinjiang have changedconsiderably after the subsequent decades, this standard no longer accurately reflects soil Znsupply threshold. Then, to evaluate a Zn fertility index that accurately reflect soil real Znstatus is not only valuable for understanding soil Zn abundance in this area but also withimportant agricultural practical significance. Therefore, this study was conducted to evaluatethe state of soil Zinc in calcareous soils of Xinjiang, and to research the effects of Znapplication on yield and quality of cotton, finally to establish a soil available Zn critical indexfor cotton cultivation in Xinjiang area.On the base of studying the content of soil available Zn and Zinc fraction in differentsoils of Xinjiang region, three calcareous soils from Xinjiang, Shandong and Jiangsu wereselected to investigate the effects of soil factors such as CaCO₃, soil salinity on soil availableZn and Zn fraction, to clarify the mechanism of soil factors on soil available Zn content by theadsorption and sorption models. This research aims to provide theoretical guidance to applyZn fertilizer reasonably and improve the yield of cotton. The major conclusions of the studyare as follows.（1） The average available zinc content in three types of soils was aquic soil (0.69mg·kg^-1)>brown desert soil (0.57mg·kg^-1)>grey desert soil (0.51mg·kg^-1), the coefficient of variationwas gray desert soil>aquic soil>brown desert soil. Soil available Zn concentration was similarin different soil types in Xinjiang, however, the total Zn content varied greatly. Soil total zinccontent in southern Xinjiang was higher than that of northern Xinjiang, and with greatervariability.In the Zn fractal content, the component’s contents of SBO, CARB, OxMn, WBO andAOFe were aquic soil>brown desert soil>grey desert soil. The percentages of WBO, CARBand SBO were highly relevant to the contents of CaCO₃and physical clay. The relativepercentages were significantly or highly significantly positive correlatted in physical claycontent and WBO, CARB, SBO. The content of WBO remarkably influenced the content ofExc. There was a significant positive correlation between WBO and CARB. The content ofsoil available Zn was remarkably influenced by WBO and CARB.（2） Zinc application contributes to cotton yield in most of soil types, and improve thebiomass of the shoot of cotton, the accumulation of yield, and increases the zinc uptake ofcotton, but its effect on the biomass of roots is not noticeable. The relative yield of cotton andavailable zinc content of soil are positively related. The critical index of zinc deficiency is0.6mg·kg^-1. At present the available zinc contents of the calcareous soils in Xinjiang are mostly at medium or low levels.（3） Zn application significantly increased the yield of cotton, improve the biomass ofcotton, contributed to boll number per plant, boll weight and lint percentage. Soil applicationof Zn on cotton yield increasing rate was ranging from1.14%to4.80%, while foliarapplication of Zn was ranging from1.10%to6.11%; Application of Zn fertility increased N、P and K absorption of cotton. The P/N rate increased from0.26to0.30and K/N rate increasedfrom1.04to1.34; under the different Zn application practices, foliar application of Zn can notobviously improve the fiber length, uniformity and elongation of cotton, however, soilapplication of Zn20kg·hm^-2significantly reduce the micron value; soil application of Zn at10kg·hm^-2and20kg·hm^-2significantly improve the fiber length and strength, decrease theuniformity and micron value. Soil application Zn is an important way to improve the bollnumber. On the base of improving boll number stably, foliar application of Zn at floweringstage not only improve the boll weight, but also improve the adsorption of N, P, K.（4） Exteral calcium carbonate remarkably decreased the content of soil available Zncontent, the order of available Zn reduction was CaCO₃20%>10%>5%>0%. The order ofCaCO₃impacts on the content of soil available Zn was Paddy soil>Brown soil>Gray desertsoil. The content of soil available Zn was highly negative relevant to the contents of CaCO₃and the correlation was best in Gray desert soil（r=-0.8628**）. The falling range of soilavailable Zn of Paddy soil, Brown soil and Gray desert soil, cultured360days, were52%～77%,52%～59%,36%～58%. The available Zn of soils under different incubation timewas1d>5d>30d>90d>180d>360d. Res and COFe were the main fractions in differenttype soils, which were71.0%～73.2%and11.6%～19.9%, and the proportion of Exc wasthe least. The proportion of WBO was rather nearly in three types soils. Exc and WBOreduced and CARB increased significantly, other Zn fractions change little. The adsorption-desorption characteristics of3types was different. The capacity of Zn²⁺adsorbed by soilswas Paddy soil＜Brown soil＜Gray desert soil, the adsorption capacity increased with theinitial concentration of Zn²⁺addition. It was also observed that the amount of desorbed Znfrom Zn absorbed soil increased with the amount of soil adsorbed Zn, but much lower thanthat soil adsorbed Zn; Zn²⁺adsorption curves of3types soil could be well described byFreundlich equation with best fitness by Paddy soil （P＜0.01）. The adsorption reactionconstant A and K of Freundlich equation were Paddy soil＜Brown soil＜Gray desert soil.The content of soil available Zn was high when the soil salinity was low; the content ofsoil available Zn reduced with increasing of equilibrium time, and the falling range were4.3%,25.6%,23.5%,30.3%under cultured360days. WBO, CARB and SBO were the mainZn fraction changing largely. WBO fraction increased while CARB and SBO decreasedsignificantly. The content of WBO increased with increasing of soil sanility, while CARB andSBO decreased. These changes mainly happened in the first30days, and steady in180days.Kinetic curves of different soil salinity were similar, the adsorption of Zn increased withincreasing of equilibrium time. The higher soil salinity content, at the same equilibrium time,the more amount of adsorption; The Freundlich model was better than the Langmuir andTemkin models to decribe adsorption isotherms process. The sorption amount of Zn²⁺ increased with equilibrium time, higher salt content lead to less Zn desorption in salinity soil,the adsorption amount of Zn increased with decreasing soil salinity. The buffering capacityand adsorption intensity of soil Zn decreased by leaching.There is a close relationship between the content of soil CaCO₃, soil salinity and Zn²⁺amount in soils desorption-sorption process. The high CaCO₃content or high salinity content,lead to lower available Zn. Therefore, adjust in the application amount and methods of Znfertilizer are needed for different types of calcareous soils and saline-alkali soils.