Effects Of Potassium Application On Soil Quality Evolution And Crop Production In Lou Soil

No-to-less application of potassium（K）fertilizer prevails in northwest China with K-rich soils,and undoubtedly results in K-deficit,and ultimately devasts the sustainability of crop production system.Considering the little information on soil quality evolution and crop yield dynamics,this study was conducted in a long-term field experiment of the Chinese National Soil Fertility and Fertilizer Efficiency Monitoring Station treated with no fertilizer（CK）;mineral N and P fertilizer（NP）;and mineral N,P and K fertilizer（NPK）,and a pot experiment(K application rates:0,270,540,1080,2160 kg K₂O ha^–1),and aimed to inverstigate the responses of soil quality and crop yield through determining soil chemical properties,enzyme activities,microbial communities,crop root,aboveground biomass,and crop yield,and thus provide scientific basis for optimizing K-fertilization.The main results obtained are as follows:（1）Long-term NP and NPK fertilization significantly increased soil quality index（SQI）scores and wheat grain yield by mediating soil fertility,which was characterized by a significant decline in soil p H and increase in soil organic carbon（SOC）,total N,available N（AN）,available P（AP）,enzymatic activities,and the abundance of total bacteria,fungi,and actinomycetes,when compared to CK.NP exhibited significantly higher SOC,AN,AP,microbial biomass C（MBC）and N（MBN）,N-acetyl-glucosaminidase,total bacteria,and fungi values compared to NPK;the opposite was true for soil p H and available K.the differences in wheat grain yield were not statistically significant,while SQI scores in NP（0.86±0.02）were appreciably higher than NPK（0.79±0.03）,which was attributed to the differences in MBC,MBN,and microbial communities.Redundancy analysis indicated that SOC was the key variable affecting enzymatic activities and microbial communities.The PLS-PM revealed that fertilization-induced changes in SQI were primarily associated with soil microbiological properties（e.g.,microbial community composition）,while fertilization-driven increases in wheat grain yield were regulated by the soil nutrients.（2）The plant height,aboveground biomass and grain yield were parabolically correlated with the increase of K application rates,reaching the maximum maize yield of112.7 g pot^-1at the K rate of 388.8 kg ha^-1,the maximum wheat biomass of 62.78 g pot^-1at the K rate of 499.5 kg ha^-1,and the maximum maize biomass of 182.1 g pot^-1at the K rate of 513.0 kg ha^-1,respectively.By contrast,no significant difference was observed for wheat yield between K-fertilization treatments.K-fertilization significantly increased increased100 grain weight of wheat and maize,when compared with CK.（3）The plant height,wheat yield and aboveground biomass was parabolically correlated with the increase of K application rates in wheat-summer fallow system,reaching the maximum wheat yield of 34.06 g pot^-1at the K rate of 207.9 kg ha^-1,and the maximum wheat biomass of 85.87 g pot^-1at the K rate of 378.0 kg ha^-1.Relative to the CK,K-fertilization significantly increased 100 grain weight of wheat,while there was no significant difference in the numbers of wheat ears among K-fertilization treatments.Collectively,high application of K fertilizers in K-rich soils may negatively affect soil quality and crop growth,and field experiments are further needed to testify the appropriate amount of K application rate in K-rich soils.