In the Northern Great Plains, grasslands have been rapidly converted to croplands over the last 10 years. The grassland conversion was mostly concentrated in the Dakotas, east of Missouri River (Wright and Wimberly, 2013). This conversion can potentially reduce soil health. Introducing livestock into arable cropping systems can improve soil health and provide economic benefits.
Benefits of the integrated crop livestock systems
In the integrated crop livestock systems, cover crops and crop residue provide feed to livestock, while plants capture nutrients from the livestock waste. Potential economic benefits include reduced fertilizer cost for the cash crop, yield/profit increase from subsequent cash crop, and additional cost savings from supplemental hay. Different species of cover crops (such as legumes and non-legumes) are generally preferred in the field to get maximum benefits.
The use of cover crops will not only provide economic benefits but can also be used to achieve multiple environmental benefits. For example, the cover crops planted after harvesting main crop can reduce N loss by absorbing residual fertilizer N (Huntington et al., 1985). Moreover, cover crops provide vegetal cover during critical periods, which can significantly reduce the soil loss rate of croplands.
Short-term impacts of grazing cover crops on soil health
There are so many benefits with these integrated systems, however, there are still some concerns regarding the role of hoof traffic from livestock that can adversely affect the near-surface soil conditions, soil health and hydrological properties. The use of a diverse cover crop mixture such as radish, peas, oats, lentils, and sorghum sundangrass can provide increased biomass on the soil surface that can alleviate the compaction impact under these integrated crop-livestock systems.
In South Dakota, a study funded through NRCS-CIG grant was conducted to test the short-term impacts of grazing cover crops on soil health. Soil samples were collected after the completion of an autumn grazing cycle (6 heifers per 1.4 ha). Results from this study, which included grazed and un-grazed cover crops, showed that short-term grazing did not have negative impact on the soil properties, including soil water retention, bulk density, soil organic carbon and total nitrogen contents.
Advice and future studies
In the region comprised of North Dakota, South Dakota, Nebraska, Minnesota, and Iowa, moisture is sometimes limited. During the 1980-2010 period, the 5-state average annual average rainfall, average minimum temperature and maximum temperature are 660 mm, 1.3¬∞C, and 14.2¬∞C, respectively. Therefore, to ensure cover crops have sufficient time and moisture to establish, it is advisable to use cover crops after small grain harvest during a 3-yr rotation in a corn-soybean-oat or wheat rotation.
There is a strong need to explore ways to improve economic and environmental sustainability of agricultural systems by integrating crop and livestock enterprises. Our recently funded projects through NRCS and USDA-CAP will help in providing short-term and long-term impacts of cover crops, grazing and grazing cover crops on soil health and crop productivity. The USDA-CAP project is a multi-institutional funded project that will focus on promoting the integrated crop-livestock systems in the North Central Region for improving food security.