Does increased cropping intensity translate into better soil health in dryland wheat systems?

Despite reliable grain yields, the 13-month fallow period in winter wheat (Triticum aestivum L.) - fallow systems (WF) in low precipitation zones (<350 mm annually) poses several challenges including soil erosion, soil organic matter (SOM) decline, weed management, and overall soil health degradation. Therefore, considerable research efforts are focused on reducing the frequency of fallow and reducing or eliminating tillage. We compared the widely practiced 2-year WF rotation to two 3-year crop rotations with only one year of fallow and continuous annual spring cropping. These systems have been evaluated over the past 10-plus years using undercutter conservation-till and no-till practices in a large-scale and long-term cropping systems experiment near Ritzville, WA USA. To date there is limited research-based information about the influence of these intensified crop rotations using conservation- and no-till compared to traditional conservation-till WF on soil health indicators, particularly microbial activity, and microbial community dynamics in the dryland region of inland Pacific Northwest (iPNW). This study was conducted as a part of Soil Health Institute's North American Project to Evaluate Soil Health Measurements (NAPESHM). We leveraged the aforementioned ongoing long-term (25-year-old) experiment to obtain these data. Soil samples were collected at 0–15 cm depth from different crop rotation treatments that included, 1. winter triticale (X Triticosecale Wittmack)-spring wheat-no till fallow (WT-SW-NTF); 2. continuous annual no-till spring wheat (CSW-NT); 3. winter wheat-undercutter conservation-till fallow (WW-TF); and 4. winter wheat-spring wheat-undercutter conservation-till fallow (WW-SW-TF). Soil samples were analyzed for an array of soil health indicators. Out of the 21 tested soil health indicators, eleven indicators were significantly influenced by crop rotations. These were SOM, carbon mineralization potential (24-h respiration), water extractable carbon (WEC), active C, potentially mineralizable nitrogen (PMN), water extractable nitrogen (WEN), soil pH, NO₃-N and NH₄-N, phosphatase enzyme activity, and wet aggregate stability (WAS). Within responsive indicators, all C-related biological indicators (SOM, WEC, active C, and 24-h respiration) were highest under WW-SW-TF rotation while N-related indicators (WEN, PMN, and inorganic N) were highest under CSW-NT rotation. The improvements in aforementioned soil properties in the 3-year winter wheat-spring wheat-undercutter conservation-till fallow rotation was likely because of the higher crop biomass production in this rotation as compared to the other tested rotations.