| Rain-fed cropland in Inner Mongolia was characterized by drought and lack of water,high evaporation,low soil water holding capacity and crops yield,they limited sustainable development of agricultural production in rain-fed regions,and thus we select bentonite as a soil amendment.Combined continuous five-year field experiments with incubation experiment in the Lab,effects of different bentonite rates on millet growth,photosynthetic characteristics,soil properties,microbial community structure and CO2 emission were investigated,we can illustrate ecological mechanism of bentonite on soil water holding capacity and millet yield increase,and thus we can provide theoretical basis and technical support for increasing soil water holding capacity,and crop yield and economic return in rain-fed regions.Results showed as follows:1.Appilcation of bentonite amendment significantly(P<0.05)increased millet emergence,plant height,above-ground dry matter accumulation,net photosynthesis(Pn),transpiration(Tr),soil plant analysis development(SPAD)and leaf water use efficiency(WUE)by 1.51%-18.01%,0.63%-25.17%,0.27%-187.03%,3.15%-32.49%,1.10%-20.92%,0.24%-14.07%and 1.10%-20.92%,respectively.2.Application of bentonite amendments significantly(P<0.05)enhanced millet grain yield and above-ground biomass by 2.59%-21.51%and 2.04%-39%,spike number per hector and 1000-kernel weight increased by 1.87%-33.33%and 0.12%-16.16%,respectively,however,it had no significant(P>0.05)effect on kernels per spike.Grain crude protein,fat and fiber increased by 3.24%-27.43%,0.31%-10.06%and 0.29%-20.40%.Water use efficiency(WUE)increased by 1.51%-29.32%over five years.From the model for the five years combined,the optimum treatment for grain yield and above-ground biomass were 26.7 and 24.3 Mg hm-2.3.Bentonite amendments significantly(P<0.05)affected soil moisture in 0-60 cm layers,soil water storage for 0-100 cm layer and aggregate in 0.25-2 mm class,decreased soil bulk density in 0-40 cm and aggregate in 0.05-0.25 mm class,but it didn't affect aggregate in either>2 mm or<0.05 mm class;significantly(P<0.05)increased soil organic carbon,total nitrogen and total phosphorus content,decreased soil electrical conductivity,but it had a small effect on pH;significantly(P<0.05)improved soil microbial carbon,nitrogen and phosphorus,and increased soil enzyme activity.4.Soil microbial community structure by second generation high-throughput sequence method was measured.Compared to CK,application of bentonite amendment increased soil bacteria relative abundance and diversity,affected soil community composition,dominant bacteria included Acidobacteria,proteobacteria,Bacteroidetes,Actinobacteria and Chloroflex at the phylum level,and bentonite increased relative abundance of Acidobacteria and Bacteroidetes by 29.63%and 46.74%,decreased relative abundance of proteobacteria,Actinobacteria and Chloroflex by 32.78%,16.84%and 33.86%;bentonite also affected relative abundance of some functional bacteria,such as Pedomicrobium and Gemmatimonas,decreased relative abundance of Bacillus,Rhizobium and Bradyrhizobium by 42.06%,50.81%and 68.69%.Bentonite increased fungi abundance,decreased fungi diversity;bentonite amendment decreased relative abundance of Fusarium and Gibberella by 51.62%and 22.60%indicating that it will be beneficial to control plant-pathogen growth in soil.5.Results in incubation experiment showed,compared to CK,that bentonite decreased CO2-C accumulative emission in both sandy and clay loam soils;decreased glucose use efficiency,and had a greater effect in sandy loam soil.Incubated 55 d,bentonite decreased nitrate content in both sandy and clay loam soils by 2.42%-13.53%and 10.55%-36.38%,respectively;increased ammonia content by 13.08%-197.17%in sandy loam soil;decreased ammonia content by 4.28%-79.40%in clay loam soil.6.The amendment effects on soil water holding capacity were affected by climate in different years,soil layer,crops growth and bentonite rate.Under relatively droughty conditions,bentonite amendment had greater effects on crop growth and soil properties;the amendment effects were the greatest at 70 d or 90 d after millet sowing;the amendment effect was largest in 10-20 cm layer,and it showed an increasing trend over time in the deeper layer(20-40 cm);the amendment effects of higher rates bentonite had an increasing trend over years,but lower rates bentonite had no significant(P>0.05)increasing trend over years.In the first three years,treatment with 18 Mg hm-2 bentonite had the greatest effect;in last two years,the rates of 24 Mg hm-2 and 30 Mg hm-2 bentonite led to the greatest effects,respectively.Averaged over five years,treatment with 18 Mg hm-2 had the highest economic return.7.By the non-dimensionalization and principal component analysis of all properties in fifth year after application of bentonite amendment,we defined a comprehensive evaluation of soil quality.Results showed that bentonite amendment can improve soil quality in a sandy soil,and it still had an amendment effect in the fifith year. |
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