The use of sod-based rotations is a critical facet of this research and affects the farming system in several areas. Perhaps the most important aspect is that of improving yield while improving soil health.
Much of the farmland in the Southeast suffers from a hardpan layer starting at 6-9 inch depth and continuing to 24 inches. This has a dramatic effect on crop management. Even with irrigation, it is very difficult to effectively manage water stress because the hard pan prevents deep penetration of the water and plant roots. Under these conditions water has to be applied frequently, increasing labor and equipment costs and decreasing water use efficiency. However, after bahiagrass there can be a 40 fold increase in crop roots down to a soil depth of 5 feet. This allows for a much larger volume of soil water to be accessed by the crop, increasing water extraction and water use efficiency.
Water extraction is not the only factor dramatically affected by rooting depth. Nutrient extraction is also greatly enhanced when rooting depths are increased, especially nitrates. Greater rooting depth not only increases the use efficiency of fertilizers applied, but also decreases the potential for contamination of groundwater with nitrates and other farm chemicals.
The increases in water and nutrient extraction and deep root growth in crops following bahiagrass sod is attributed to the effect that the deep penetrating roots of the grass have on soil structure, especially soil pore size and numbers. It is thought that the crop roots can penetrate the compaction layer by following the channels created by the decaying bahiagrass roots.
We expect that the need for irrigation will be reduced several ways. First, the bahiagrass will not need as much irrigation as the row crops (10 inches vs 20 inches), and half of the land will be in bahiagrass. Second, the increased water infiltration will reduce the need for irrigation in row crops. Finally, the increased root depth and density will make the row crops more efficient at extracting deeper water.
From the above, it is obvious that the use of bahiagrass in rotation with row crops has numerous advantages to increasing yield. However, bahiagrass pasture also may benefit from rotation. There is evidence that permanent grass pastures are not as productive as pastures plowed and seeded periodically. By rotation with row crops, there is the opportunity to control weeds that may have invaded the pasture and replant new or different varieties of grass.