玉米秸秆替代部分化肥提高黑土团聚体稳定性并改善土壤结构OA

[Objectives]Fertilization affects soil structure.Long-term application of chemical fertilizers tends to degrade soil structural stability and acidification.We studied the effect of integrated application of chemical fertilizer and maize straw on black soil nutrient availability,aggregate size distribution and stability,aiming to propose nutrient management for sustainable use of black soil.[Methods]A long-term fertilization experiment was established in 1989 in Gongzhuling,Jilin,under single maize cropping system.In 2010 and 2022 after harvest of maize,0-20 cm top soil samples were collected from the three treatment plots:no fertilization(CK);application of chemical N 165 kg/hm2,P2O5 82.5 kg/hm2,and K2O 82.5 kg/hm2(NPK);and combined application of NPK with maize straw 7500 kg/hm2(NPKS).The soil pH,organic matter(SOM),total nitrogen(TN),available phosphorus(AP),available potassium(AK),and exchangeable Ca2+(exCa)and Mg2+(exMg)were analyzed.A wet-sieving method was used to divide soil aggregates into four size classes:>2 mm,0.25-2 mm,0.053-0.25 mm,and<0.053 mm.The mean weight diameter(MWD)and geometric mean diameter(GMD)of soil aggregates were calculated to evaluate aggregate stability.[Results]With increasing of the experiment years,compared to the CK,NPK treatment significantly reduced the MWD by 44.8%and 22.2%,and the GMD by 59.3%and 25.6%in 2010 and 2022,respectively;and the soil exchangeable calcium content decreased significantly by 40.6%and 22.6%.The soil pH decreased significantly by 1.32 and 1.50 units within two years.Correlation analysis revealed that soil pH,exCa and organic matter were positively(P<0.05)correlated with the MWD and GMD.Long-term application of chemical fertilizers hinders the cementing process of soil particles and their agglomeration effect,significantly reducing the stability of aggregates.Compared to NPK,the NPKS treatment significantly increased the content of>2 mm aggregates by 159.0%and 109.2%in 2010 and 2022,respectively,thereby increased the MWD by 33.6%and 46.0%,and the GMD by 61.1%and 68.9%,respectively.The content of soil organic matter increased by 14.7%and 28.3%,the content of exCa increased by 121.2%and 97.9%,and the pH increased by 1.41 and 1.66 units respectively.A random forest model analysis assessed that soil pH and exchangeable calcium ions were increasingly becoming the key factors in enhancing the stability of black soil aggregates,while the relative importance of soil organic matter dropped from the first place to the fourth.[Conclusions]In black soil,substitution of part chemical fertilizers with maize straw can significantly increase the organic matter and exchangeable Ca content,alleviate the decline of soil pH,which is conducive to the formation of macroaggregates and enhancement of the aggregate stability.Thus,the approach is an optimal nutrient management for maintaining soil fertility and sustaining structural stability in black soil of northeast China.