Actinobacteria and Nitrogen Fractions Drive Soil Multifunctionality and <i>Camellia oleifera</i> Abel. Fruit Setting Rate: Based on Field Study With Cow Manure Amendment

ABSTRACT Revealing the linkages among camellia ( Camellia oleifera Abel.) growth, soil multifunctionality, and cow manure application rate might offer new light on the optimization of cow manure application rate and ecological and economic benefits in camellia plantations. However, studies have focused on the effect of cow manure application on soil multifunctionality and camellia growth, but the trade‐off between cow manure application rates and soil multifunctionality and camellia growth remains unclear. Thereby, we analyzed the linkages among fruit setting, soil nutrient availability and multifunctionality, and microbial communities with four different cow manure application rates (control without cow manure (CK); 10 kg plant −1 (CL); 20 kg plant −1 (CM); and 30 kg plant −1 (CH)). Soil multifunctionalities in the CL, CM, and CH treatments were increased by 39.74%, 66.57%, and 68.36%, respectively, compared to the CK treatment. The fruit setting rates in the CL, CM, and CH treatments were 2.00, 4.75, and 4.50 times of the CK treatment, respectively. Cow manure applications significantly enhanced soil total nitrogen (N), ammonium nitrogen (NH 4 + –N), nitrate nitrogen (NO 3 − –N), and microbial biomass nitrogen (MBN) contents, which had significant and positive effects on soil multifunctionality and fruit setting rate. Moreover, increases in soil mineral N contents stimulated soil Actinobacteria growth and activity, which also drove soil multifunctionality and fruit setting rate with cow manure amendment. Given the comprehensive balance among multifunctionality, fruit setting rate, cow manure input cost, microbial characteristic, and environmental impact, the 20 kg cow manure per plant might be appropriate for camellia plantations in this study. The comprehensive balances across yield, soil, and microbial properties should be further considered in the future.