Effects Of Soil Acidification Under Drip Irrigation On Soil P And Zn Availability At Calcareous Soil And Its Biological Effects

Object: Calcareous soil, character by high p H, normally resulting in low availability of soil nutrients, it restrict crops uptake soil nutrient. Applying acidulant can reduce soil p H, improve soil nutrients availability, but the high cost limited it used for practice. Fertigation, character by its locally application of fertilizer, low dosage, high irrigation frequency, provide a new means to applying acidulant. This paper study the changes of soil p H and nutrients availability under different types of acidulant application and equivalent acidulant applied by different application pattern, the dynamics of nutrients availability and cotton yield response to acidification, to provide a new way to improve the efficiency of P and Zn resource utilization on calcareous soil under drip irrigation.Methods: Micro-plot experiment contain three treatments. Equivalent acidulant applied at different pattern:(1) all acidulant applied in a single cycle(S),(2) acidulant split applied in 6 times(M) and(3) fresh water(CK). Different types of acidulant applied by fertigation were designed in field experiment:(1) no P(NK),(2) normal fertilization(NPK),(3) sulphuric acid(SA),(4) urea phosphate(UP),(5) ammonium sulfate plus N-serve(ASN). All treatments received uniformed N, P, K nutrient(except NK), if acidulant contain N or P nutrient, same amount of nutrient was deduct from other source of fertilizer. Huiyuan 710(Gossypium hirsutum L.) was used in this study. Soil p H, Olsen-P, DTPA-Zn and inorganic phosphorus fractionations were measured in micro-plot experiment, aims to evaluate the effects of soil nutrients availability by acidulant applied pattern and the possible nutrient activation mechanism. Olsen-P, root morphology parameters and root vigor at 3 leaf–age of cotton were measured in field experiment, to study the effects of acidulant effect on cotton seeding growth at sowing stage; soil p H, Olsen-P, DTPA-Zn in different soil profile, cotton biomass and P, Zn accumulation and yield components were measured to study different acidulant acidification effects and its effects on cotton P and Zn uptake and yield response of drip-irrigated cotton.Results: 1. Micro-plot experiment indicated that same amount of acidulant applied at low dosage, high frequency significantly reduced local soil p H compared to single application under similar conditions in the field, correspondingly, Olsen-P increased significantly, while available Zn content showed no change. The decrement of soil p H and increment of Olsen-P content have significant positive correlation(R2=0.6334**), indicating that soil P activation was mainly by the acid dissolution. Analysis the changes of inorganic phosphorus fractionations showed that split acidulant application can significantly increase the content of Water-P, Olsen-P and Ca2-P, and Ca2-P content was extremely significant positively correlated with Olsen-P and Water-P content respectively, and the correlation coefficient was 0.901 and 0.725, indicating that Ca2-P was the main P source to supply available P on the tested soil. 2. Acidulant applied at sowing stage significantly decreased local soil p H, SA, UP, ASN reduced soil p H value by 0.19, 0.14, 0.16, and the increment of Olsen-P were 7.98, 6.66, 6.58 mg·kg-1 respectively, the results indicated that P availability improved by decreased soil p H. The root vigor, root morphology parameters including root length, root surface area, root volume and root length density at 3 leaf-age cotton significantly higher than NPK, the root average diameter has tendency to decrease. 3. With the increase of acidulant application, intensified acidifying effect was observed. Acidulant applied significantly decreased the local soil p H of 0-10 and 10-20 cm soil depth, and the p H decrement of SA, UP, ASN were 0.20, 0.24, 0.32 at most, respectively. Corresponding, the Olsen-P increment of SA, UP, ASN were 5.44, 6.56, 6.97 mg·kg-1 at most, respectively. UP and ASN treatment showed better acidification effects than SA, NK or NPK; but at 20-40 cm soil depth, no difference of soil p H was observed among treatments, Olsen-P and DTPA-Zn content of acidifier treatments significantly increased. The results indicated that acidify effect have accumulative effects in drip irrigation condition. 4. The acidulant application by fertigation significantly increased shoot dry matter accumulation, P and Zn uptake than NPK treatment, and P, Zn uptake in SA, UP, ASN treatments were increased by 21.1%、18.8%、28.0% and 130.82、87.09、142.10 g·hm-2 at harvest, respectively; under equivalent nutrient inputs, fertigation with acidulant resulted in seed yield of cotton increased by 12% to 16%, ASN showed the highest yield among all treatments; the P recovery efficiency, P agronomic efficiency and P partial factor productivity significantly increased, but dry matter productive efficiency and physiological efficiency of P fertilizer were decreased.Conclusions: 1. Applying acidic material in calcareous soil can reduce soil p H and improve P availability, the main phosphorus source activated by acidulant was Ca2-P, and the activation mechanism may be related to acid dissolution inhibit Ca2-P to insoluble forms of phosphate. 2. Acidulant application at sowing stage reduced soil p H, improved the availability of phosphorus, promoting the root growth at 3 leaf-age cotton stage, which promoted the nutrient uptake of cotton root and protected cotton against low temperatures at seeding stage, so it helpful for subsequent growth. 3. Acidulant applied to calcareous soil at low dosage, high frequency by drip irrigation reduced p H at 0-20 cm soil depth near root zone. The availability of soil phosphorus at 0-40 cm soil depth near root zone significantly improved by acid dissolution, and promoted P uptake of cotton. Soil zinc availability showed no significantly increase in different soil depth, but promoted nutrient uptake of plant. 4. Under equivalent nutrient inputs and management, acidulant applied to calcareous soil at low dosage, high frequency by drip irrigation system significantly increased the seed yield of cotton and the efficiency of P fertilizer compared to normal fertilization. Acidulant applied to soil by drip irrigation at low dosage, high frequency is a promise way on calcareous soil to improve the efficiency of P resource utilization. 5. In all three kinds of acidulant, ammonium sulfate showed the strongest acidification effect in this study.