Changes in biological soil health properties in response to increased crop diversity in a dryland wheat-based cropping system

Abstract Diversifying wheat ( Triticum aestivum L.)-based cropping systems can be an effective management tool to break weed and disease cycles. While extensive research has focused on the agronomic benefits of increased crop diversity in semi-arid environments, less is known about the impacts of increased crop diversity on microbial community structure and processes such as nitrogen (N) cycling. This work compared a continuous wheat crop sequence to a diverse sequence that included pea ( Pisum sativum L.), proso millet ( Panicum miliaceum L. ), safflower ( Carthamus tinctorius , L.), and spring wheat. Soil inorganic N (NO 3 -N and NH 4 -N), soil respiration, microbial biomass, enzyme activity, and microbial community alpha diversity, a measure of the number of taxa within a treatment, were determined. Soil respiration was higher (p < 0.005) in the diverse sequence while activity of N-acyl-β-D-glucosaminidase, an enzymatic indicator of C and N mineralization, was lower (p < 0.05) with a mean rate of 26.3 mg ρ-nitrophenol kg − 1 soil h − 1 and 16.3 mg ρ-nitrophenol kg − 1 soil h − 1 for the continuous wheat and diverse sequences, respectively. Soil respiration was weakly correlated to soil water content ( R 2  = 0.21) and temperature ( R 2  = 0.29) in the diverse rotation, while only weakly correlated to soil water content ( R 2  = 0.05) in the continuous wheat system (p < 0.001). The mean net N mineralized under a wheat crop during the growing season was 33.2 ± 2.5 kg ha − 1 and was not different between treatments (p > 0.05). Microbial community analysis showed no difference in bacterial alpha diversity, while fungal community diversity was 52% lower in the diverse rotation. The results of this work suggest that specific crops in a rotation may impact microbial processes related to N mineralization and that the soil fungal community may be more sensitive to changes in crop sequence than the soil bacterial community.