Integrated crop-livestock system effects on soil N, P, and pH in a semiarid region

- Integrated crop-livestock systems (ICLS) may sustainably intensify agriculture.
- Meeting production and environmental goals require efficient use of plant nutrients.
- Available N and P did not accumulate under grazing compared to cropping.
- Soil acidification occurred where crop residue was grazed or mechanically harvested.
- Management targeting N conservation may mitigate soil acidification in ICLS.

Integrated crop-livestock systems (ICLS) represent a potential means to sustainably intensify agriculture. Developing ICLS that concurrently achieve production and environmental goals is contingent upon efficiently managing plant nutrients in time and space. In this study, we sought to quantify residue management and field-zone effects on soil NO3-N, available P, and soil pH over a 12 year period for an ICLS experiment near Mandan, ND USA. From 1999 to 2011, soil NO3-N and available P were measured in three residue management treatments (grazed, mechanically harvested, and no residue removal) every third year across a 122 cm soil depth, while soil pH was measured prior to deploying ICLS treatments in 1999 and again in 2011. Residue management did not affect soil NO3-N or available P at any depth for any year (P > 0.1), implying no accumulation of available N and P under grazing compared to cropping. Similarly, no differences in available N and P were observed across grazed sampling zones. Soil nutrients, however, increased or fluctuated greatly over the 12 year period, suggesting a need for adaptive nutrient management. Soils became more acidic between 1999 and 2011, with the greatest decreases in soil pH at 0-8 cm under grazing (0.74 pH unit decline; P = 0.0581) and mechanical harvest (0.86 pH unit decline; P = 0.0138). Management interventions targeting nutrient conservation may serve to mitigate N and P loss and soil acidification in ICLS.