Functional diversity of soil microbial communities in response to supplementing 50% of the mineral N fertilizer with organic fertilizer in an oat field

The effects of supplementing 50% of the mineral N fertilizer with organic fertilizer on the metabolism and diversity of soil microbial communities in an oat field were investigated using Biolog-Eco plates. The experiment consisted of five treatments: no fertilizer (CK), mineral N fertilizer applied at 90 and 45 kg ha−1N in the form of urea (U1 and U2, respectively), and U2 supplemented with organic fertilizer in the form of sheep manure at 90 and 45 kg ha−1N (U2OM1 and U2OM2, respectively). Each treatment had three replications. The experiment was conducted in 2018 and 2019 in Pinglu District, Shanxi Province, China. The carbon source utilization by soil microbial communities, such as amino acids, amines, carbohydrates, carboxylic acids, and polymers, increased when 50% of the mineral N fertilizer was replaced with organic fertilizer in both years. This result was accompanied by increased richness, dominance, and evenness of the microbial communities. The utilization of amino acid, amine, and carboxylic acid carbon sources and community evenness were further improved when the organic fertilizer amount was doubled in both years. Biplot analysis indicated that amines and amino acids were the most representative of the total carbon source utilization by the soil microbial communities in both years. The highest oat yield was achieved at a total N application rate of 135 kg ha−1in the treatment involving 45 kg ha−1N in the form of urea and 90 kg ha−1N in the form of sheep manure in both years. It was concluded that the application of 50% of the conventional rate of mineral N fertilizer supplemented with an appropriate rate of organic fertilizer enhanced both the functional diversity of soil microbial communities and oat yield. Amine and amino acid carbon sources may be used as a substitute for total carbon sources for assessing total carbon source utilization by soil microbial communities in oat fields in future studies.