Effects of combined biochar and organic matter on soil fertility and maize growth

As a new functional material, biochar can increase soil carbon pool, improve soil quality and increase crop yield because of its particulate physical and chemical properties and is thus widely used in agriculture. However, studies on the comparison between biochar and traditional organic matter and their combined application are relatively rare. Thus a pot experiment was conducted to study the effect of the separate application of biochar, straw and chicken manure or their combined application on nutrient status, enzyme activity of soil and maize growth in fluvo-aquic loamy and sandy soils. Principal component analysis and simple correlation analysis were also used to synthetically evaluate the effects of different treatments and to determine the main driving factors of maize growth. All in all, a total of six treatments were conducted:control (CK), biochar (BC), wheat straw (WS), chicken manure (CM), wheat straw plus biochar (WS+BC) and chicken manure plus biochar (CM+BC). The results showed that all treatments increased maize biomass and height in sandy soil, the order of treatments in terms of maize growth was CM+BC=CM > WS+BC, BC > WS > CK, and manure could also increase maize biomass and height in fluvo-aquic loamy soil. Biochar and organic matter increased soil organic matter content, with the former particularly inducing a sharp increase. Different treatments showed different effects on soil nutrients and enzyme activities in both fluvo-aquic loamy and sandy soils. Chicken manure respectively increased soil available N by 22.08% and 26.67%, available P by 91.92% and 53.65%, and urease activity by 40.54% and 36.94% in fluvo-aquic loamy and sandy soils. Biochar respectively increased soil available P by 83.52% and 89.91%, soil available K by 79.38% and 127.02%, and soil catalase activity by 3.41% and 11.22% in the two soil types. Wheat straw respectively increased soil available K by 49.48% and 63.02%, soil β-glucoside enzyme activity by 51.86% and 59.09% in both fluvo-aquic loamy and sandy soils. Overall, combined application of biochar and manure or straw complemented each other and thereby improved more comprehensively soil fertility. Principal component analysis and correlation analysis suggested that maize biomass and height were highly significantly correlated with the second principal component score (PC2), which led to the positive changes in soil N and P pool. Therefore, among the three forms of organic matter, chicken manure influenced soil N and P contents and the related enzyme activities the most. Straw greatly influenced soil K and cellulose degradation-related enzymes, while biochar more evenly enhanced soil fertility which led to the most comprehensive gains in soil fertility. Straw or chicken manure, combined with biochar, more comprehensively improved soil fertility.