The Effect And Its Related Mechanism Of Organic Amendments On Soil Water-Air Transport Properties And Crop Growth

Organic materials are the renewable natural resource,which can provide organic carbon,nitrogen,phosphorus,potassium and trace elements for plants.The key is scientific and reasonable utilization of organic materials.Recycling organic materials by field application has been a dominant way to prevent soil degradation and sustain crop production.Although organic amendments are generally effective for improving soil properties and crop productivity,the type of applied organic amendments affects these parameters and needs to be considered when planning field application.To achieve the maximum crop productivity and environmental benefits,it is thus necessary to explore the effect and its related mechanism of various types of organic amendments on water-air environment of root-zone soil and the crop production in the Guanzhong Plain of China.Thus,a two-year（June2014-June 2016）field experiment was conducted with a fixed plot test on a Lou soil（Eum-Orthic Anthrosols）to investigate the impacts of organic amendments on soil carbon pool,soil structure,soil water-air transport properties and grain yield in a winter wheat-summer maize rotation system.The five treatments were:application of mineral fertilizer alone（control,CK）and along with 20000 kg hm^-2 of wheat straw（MWS）,wheat husk（MWH）,farmyard soil（MFS）,and bioorganic fertilizer（MBF）.The main conclusions were as follows:（1）Organic amendments generally increased soil organic carbon content and sustained soil structure.Compared with the CK treatment,organic amendments generally increased organic carbon and its component contents after two years.For example,organic amendments significantly increased the mean soil organic carbon content,total organic carbon storage and organic carbon sequestration in the 0～40 cm soil layer.Organic amendments also significantly increased soil active organic carbon,soil dissolved organic carbon and soil microbial biomass carbon contents at the 0～10 cm soil depth.Soil carbon pool management index under organic amendments also was significantly higher than that of the CK treatment at the 0～10 cm soil depth.The total soil organic carbon content was highest in the MWS treatment,while the MBF treatment had higher organic carbon component contents than other treatments.Meanwhile,organic amendments improved soil structure by increasing water stability of three aggregate classes（>5 mm、2～5 mm、1～2mm）,>0.25 mm soil water stable aggregates,soil aggregates mean weight diameter and geometric mean diameter,as well as by decreasing the fractal dimension of soil aggregates in the 0～40 cm soil layer after two years.The MWS and MBF treatment had the stronger improvement in soil structure than other organic amendment treatments.（2）Generally,organic amendments enhanced soil hydraulic properties and improved soil water conservation.Organic amendments significantly enhanced soil hydraulic conductivity at the 0～20 cm soil depths compared to the CK treatment over two years,such as increasing initial infiltration rate,steady infiltration rate,average infiltration rate,90 min cumulative infiltration,as well as saturated hydraulic conductivity.These parameters were highest in the MWS treatment（greater by 5.3～8.8 times compared to the CK treatment）at the 0～10 cm soil depth and in the MBF treatment（greater by 2.0～4.5 times compared to the CK treatment）at the 10～20 cm soil depth,respectively.Meanwhile,the MBF treatment also significantly improved soil hydraulic conductivity compared to the CK treatment at the 20～40 cm soil depth.However,soil holding water capacity was less sensitive than the soil hydraulic conductivity to the application of organic amendments.The MWH,MFS and MBF treatments only significantly increased soil field capacity and available water content at the 10～20 cm soil depth compared to the CK treatment over two years.In addition,organic amendments increased the soil water content and soil water storage across the whole soil profile（0～100 cm）at maturity in summer maize seasons,and the MBF treatment performed better.The MWS treatment had the stronger improvement in soil water contents in the 50～90 cm soil layer and soil water storage in the 0～100 cm soil layer compared with the CK treatment at maturity in winter wheat seasons,particularly in dryer season.（3）Organic amendments generally increased soil macro-porosity and soil pore continuity and hence improved soil air transport properties.Compared to the CK treatment,organic amendments improved soil pore size distribution and promoted the increase in macro-porosity over two years.This was especially true at the 0～10 cm and 20～30 cm soil depths,where incorporation of organic materials significantly（p<0.05）increased soil macro-porosity by 12.3%～136.4%compare to the CK treatment over two years.The significant（p<0.05）increase in the macro-porosity was also recorded in the MWS treatment at the 10～20 cm depth compared to the CK treatment after two years.With regards to soil air permeability,the MWS and MWH treatments led to significantly（p<0.05）better soil pore continuity and hence higher soil air permeability at the 0～10 cm soil depth,compared to the CK treatment,while the MBF treatment yielded significantly（p<0.05）higher soil air permeability at both the 10～20 cm and 20～30 cm soil depths.Soil air permeability was significantly related to soil organic carbon content,water stable aggregate content,soil total porosity,macro-porosity,pore continuity and soil bulk density,while was not associated with soil infiltration parameters and soil saturated hydraulic conductivity.（4）Organic amendments generally stimulated crop aboveground and belowground growth,increased crop grain yield and water use efficiency in a summer maize-winter wheat rotation system.Over the two years,organic treatments increased the annual aboveground biomass by 4.58%～20.63%,the annual grain yield by 9.36%～25.39%,the annual water use efficiency by 10.16%～30.69%and the annual precipitation use efficiency by 9.90%～25.23%compared to the CK treatment.Also,organic amendments performed positive improvement in plant height,leaf area index,chlorophyll content and photosynthetic rate compared to the CK treatment.Generally,the MWS and MBF treatments had better performance in crop growth parameters,grain yield and water use efficiency.Meanwhile,compared to the CK treatment,organic amendments generally improved the root length density（RLD）and root mass density（RMD）of maize and wheat.With regards to the maize root growth,the MWS treatment produced the highest RMD at the whole growing season and the highest RLD at the early growth stage,while the MWH treatment had highest RLD at the middle and later stages of maize.At maturity,organic amendments increased the RLD and RMD in the 60～100 cm soil layer compared to the CK treatment.With regards to the wheat root growth,organic amendments significantly increased the RLD and RMD in the 0～20 cm soil layer and the 60～100 cm soil layer（except for the MWS treatment）at the flowering stage.The responses of RLD and RMD to WSA and ε₁₀ were well described by the quadratic polynomial equations based on all treatments,and showed that the mean values of WSA（42.9%）and ε₁₀（15.4%）can be considered as an optimum value for the root growth of winter wheat in similar environments.（5）In the Guanzhong Plain,we suggest that the MBF treatment is an efficiency method for improving soil water-air transport properties and crop growth.The soil water-air transport parameters and crop growth parameters were comprehensively evaluated by using the factor analysis method,fuzzy evaluation and hierarchical cluster analysis.The results showed that organic amendments could optimize water-air environment of root-zone soil and promote the crop growth.The MWS and MBF treatments had the best improvements,followed by MWH and MFS treatments,and the CK treatment was worst.Additionally,the MWS treatment had the strongest improvement on soil water-air transport properties at the 0～10 cm soil depth,and the MBF treatment had the strongest improvement at 10～20 cm and 20～30 cm soil depths.Synthetically,to alleviate sub-surface soil compaction,improve soil water-air transport properties and promote crop growth,application of bioorganic fertilizer was highly recommended in the Guanzhong Plain.