A long-term integrated crop, beef cattle, and soil health research project at the Dickinson Research Extension Center is designed around a no-till diverse multi-crop rotation (spring wheat, cover crop, corn, pea-barley, sunflower). In this crop and animal production system, beef cattle graze three of the crops in the rotation: pea-barley mix (60% pea, 40% forage barley), silage type corn, and a multi-specie cover crop to document microbial, fungal, and nutrient change over time and space. Precipitation during the first five-year crop rotation was normal to slightly above normal. However, the second five-year rotation was drier than normal. During the period 2016-2020, drought reduced precipitation resulting in nutrient concentration, reduced microbial activity, and pH decline. Previous nitrogen mineralization of soil organic matter (SOM) in the crop rotation suggests that 8.4 mg N/kg of soil are mineralized for each 1.0% increase in SOM. The mean SOM content of soils in the study is 3.97%. Soil microbial analysis was conducted by Ward Laboratories, Inc., Kearney, NE 68848.

Key Effects of Drought on Semi-Arid Soils in Western North Dakota:

·        Periods of reduced precipitation inhibit soil nutrient solubilization and

translocation: negatively impacting soil microbial respiration, fungal activity, plant nutrient supply, crop yield, and animal grazing days.

·        With drying, soil pH declined as soluble salt became more concentrated resulting in a more acidic soil condition.

·        Reduced precipitation contributes to minimized plant and root growth, resulting in reduced SOM content and nitrogen mineralization.

·        For most crops in the diverse crop rotation, the percent of microbial active carbon, organic C:N ratio, and organic N:inorganic N ratios declined.

·        24-hour microbial respiration (Haney Test) provided measurements of microbial community and organismal diversity.

·        Mean soil microbial biomass under drought conditions (2017) was 1,637 ng/g of soil.

·        Microbial biomass with normal precipitation (2019) was 4,804 ng/g of soil; a 193.5% increase.

·        Arbuscular mycorrhizal fungi (AMF) did not reestablish in sunflower, cover crop, corn, and the spring wheat-control, and only slight levels of AMF were measured in the pea-barley and spring wheat-rotation crops.

·        Declining soil pH approaching 5 or less reduces copper, manganese, zinc, and aluminum plant availability. At pH levels less than 5 (strongly acidic), unhydrated aluminum (Al³⁺) is toxic to plants.

·        Mean drought effected soil pH declined 9.5% to a mean crop pH value of 5.95. At this soil pH value, aluminum is sufficiently hydrated to be non-toxic.

·        Return to normal precipitation (2019) increased the crop rotation pH mean to 6.58.

·        Within the rotation, the deep rooting crops sunflower and corn have the potential to bring cations to the soil surface to support pH buffering.