Effects of fertilizer managements on crops nitrogen use efficiency and disease incidence in fluvo-aquic and red soils

Objectives This study investigated the effects of N management practices on crops productivity, N utilization efficiency and disease incidence of maize.

Methods Five consecutive years of field trials were conducted in fluvo-aquic soil of Xuchang City (XC) of Hennan Province, and red soil of Qujing City (QJ) of Yunnan Province since 2016, respectively. The nine treatments included: no N control (CK), conventional N fertilizer rate (N), reducing 20% of conventional N input (80%N), and the combination of 80%N with straw return (80%NS), nitrification inhibitor (80%NI), green manure (80%NGM), asymbiotic N₂-fixing bacteria Klebsiella variicola inoculant (80%Nkle), biochar + straw return (80%NBS), biochar + nitrification inhibitor (80%NBI). The productivity and N utilization of crops were measured in each season, and maize fungal disease index (leaf blight) and insect pest corn borer (Ostrinia nubilalis) were monitored since 2018.

Results Compared with N treatment, 80%NBS and 80%NBI significantly increased soil organic matter and total carbon in red soil of QJ, the other treatments had no significant effect on soil physicochemical properties of the two experimental sites. In XC, 80%N significantly decreased the crops productivity, while 80%NI and 80%NKle maintained crop productivity and increased N use efficiency by 21%−34%, and reduced N surplus by 33%−42% simultaneously. In QJ, 80%N did not cause crop yield decrease, but increased the N use efficiency (NUE) by 29.4% and reduced N surplus by 31.1% simultaneously. Generally, corn borer is more serious in XC than in QJ, the pest incidence in XC (P<0.05) was positively correlated with the maize yield and total N uptake. 80%NGM treatment significantly decreased the occurrence of corn borer in QJ. 80%NS treatment significantly increased the disease index of maize leaf blight in XC. The leaf blight disease in QJ was serious, and the disease index was (P<0.05) negatively correlated with plant N uptake, stem and leaf N contents, and soil total N.

Conclusions In XC and QJ, reducing 20% of conventional N fertilizer and combined with application of nitrification inhibitors, biochar or diazotroph inoculant is effective in maintaining crop yield and NUE, and decreasing soil nitrogen surplus. Straw return might increase the disease incidence of leaf blight in XC, while green manure incorporation could decrease corn borer holes and enhance corn yield in QJ. Further studies need to conducted for the relationship of nutrient cycling managements with the occurrence pf pest disease.