Effects Of Straw Pretreatment On Soil Water And Fertilizer Factors And Crop Yield

Through carrying out a two-year field experiment at Irrigation Experiment Station of Shaanxi Province, we investigated how the incorporation of pretreated straw affected soil water and fertility factors, crop development and yield in the arid area; and based on the field experiment results, the most suitable straw pretreatment pattern was selected; by incubation experiments, we tentatively revealed the working mechanisms for the field effects of pretreated straw, aiming at evaluating effects of straw pretreatment on soil structure, soil moisture characteristics, and the mineralization of straw itself. 1. Effects of straw pretreatment on soil moisture, soil fertility and crop yield in dryland(1) Among several straw pretreatments, straw comminution benefited the wheat tillering before winter, while soil water was lost faster, and wheat grew slowly in the later stage; in the stage of greening, the pretreatment of comminution and ammoniation obviously increased wheat tillering, followed by the combined applicaion of ammoniated straw and calcium sulfate. The straw pretreatments of long-cutting and comminution both affected wheat growth to some extent, but less than the application of comminuted-ammoniated straw and the combined application of comminuted-ammoniated straw and calcium sulfate.(2) In terms of crop yield, in year of 2010-2011, the highest yield occurred under the straw pretreatment of comminution-ammoniation, followed by the mixed application of comminuted-ammoniated straw and calcium sulfate, and long-cutting pretreatment in the last place; in year of 2011-2012, compared with other straw pretreatments, comminution –ammoniation increased by approximately 6.7%-14.8%, slightly higher than the combined application of comminuted-ammoniated straw and inorganic amendment. Both the above straw pretreatments not only increased crop yield, but also increased water use efficiency.(3) Compared with long-cutting and comminution, the mixed application of comminuted-ammoniated straw and calcium and the single application of comminuted-ammoniated straw, increased the soil moisture content when sowing, the soil water amount in the stage of grouting and the soil water content while harvesting, indicating that both the above straw pretreatments were effective measures for field water conservation. While taking into account the soil water availability in the dryland water conservation, the pretreatment of comminution-ammoniation was recommended.(4) The combined application of comminuted-ammoniated straw and calcium and the single application of comminuted-ammoniated straw, both significantly increased the organic matter content in the surface soil layer, while for the sub-surface soil layer, the organic carbon content was lower. In terms of the total nitrogen content, there was a similar change to soil organic matter; while both pretreatments affected total phosphorus to a less extent. When it came to availabe nitrogen, available phosphorus, available potassium content, the amount in the upper layer was obviously higher the lower layer. However, due to the slow decomposition, the long-cutting straw and the comminuting straw affected soil nutrient to an even less extent.(5) Due to the interaction between calcium sulfate and comminuted-ammoniated straw and absorption of soil nutrient by calcium sulfate itself, the pretreatment of mixing comminuted-ammoniated straw and calcium sulfate decreased soil nutrient availability than the pretreatment of comminution and ammoniaton. Therefore, the combined application of calcium sulfate and comminuted-ammoniated straw better conserved soil nitrate nitrogen. To increase soil nutrient content and enhance soil nutrient availability in dryland areas, we recommend the adoption of returning comminuted-ammoniated straw to field; while considering the conservation of soil inorganic nitrogen, we recommend the combined applicaton of calcium sulfate and comminuted-ammoniated straw. 2. Mechanism for field effect of pretreated straw(1) The single application of comminuted-ammoniated straw or the combined application of comminuted-ammoniated straw and inorganic soil amendment, both significantly improved soil structure. By the wet-sieve method, both the above straw pretreatments increased the mean weight diameter of soil aggregate almost twice(the latter higher). Long-cutting straw almost had no improving effect on soil aggregate stability and soil porosity distribution. While the single application of inorganic soil amendment effectively improved soil porosity distribution, which further inhibited soil water evaporation.(2) Compared with long-cutting straw, comminuted straw increased soil saturated water content and improved soil water retention capacity and soil water supplying capacity; comminuted-ammoniated straw or the mixture of comminuted-ammoniated staw blending with inorganic soil amendment, significantly improved the above soil water characteristics. With the application of comminuted straw or long-cutting straw, the soil water dehydration rate was higher, while for the comminuted-ammoniated straw or the mixture of comminuted-ammoniated straw, there was a lower soil water dehydration rate.(3) The comminuted-ammoniated straw had the strongest capability of decomposition, followed by the mixture of comminuted-ammoniated straw and calcium, while the comminuted straw and the long-cutting straw presented the lowest decomposition rate.