By Sjoerd Willem Duiker and Divya Pant
After excluding grazing from cropland for many years, there is new interest in integration of grazing and crop production. It can be an important component of sustainable intensification – considered by most agronomists an important strategy to meet future demands on agriculture. Sustainable intensification is defined as "a process or system where agricultural yields are increased without adverse environmental impact and without the conversion of additional non-agricultural land" (Pretty and Bharucha, 2014). Grazing crop residues and cover crops can help increase production without taking more land into production – but it is important that it does not have negative effects on sustainability. One of the main concerns of grazing relates to excessive soil compaction – which could lead to increased soil erosion and runoff.
Several studies have shown that soil compaction by grazing animals does not have to be a problem. Compaction by grazing animals is typically no deeper than 3-4 inches, and often less than that. On the other hand, heavy farm machinery with axle loads exceeding 10 tons can compact the subsoil to depths of 18 inches or more. This is important because biological and physical forces that help remediate the effects of compaction are most active near the surface of the soil. Examples of biological forces active near the soil surface are cover crop roots that act as a geotextile making soil resist compaction and while growing, restore pore spaces in the soil. Soil organisms such as earthworms, dung beetles, bacteria, and fungi are more numerous and active near the soil surface. These organisms help create pores in soil and restore soil structure. Freeze-thaw cycles and wetting-and-drying cycles, more frequent near the soil surface, have been shown to create new pore spaces as well.
Over the past two years we have been measuring the effects of grazing cover crops after corn silage and small grain harvests on four farms in Adams and Franklin Counties. The farmers had been using permanent no-tillage for more than 10 years and did not use any tillage during our study. The farmers installed high-tensile permanent fencing around the crop fields and used mobile electric fencing to split the fields in smaller sections so that beef cows could be moved daily. Animals were not allowed to go back to the sections grazed the previous day. This meant they also had to have watering systems supplying the animals with water in the small paddocks. Farmers received assistance from USDA-NRCS grazing specialists and Capital Region RC&D to develop grazing plans and install the grazing systems. Cover crop grazing after small grain harvest provided 1734 to 3342 lbs/A forage dry matter in fall, while cover crop grazing after corn silage supplied 1029-3880 lbs/A forage dry matter in spring. The crude protein content varied between 9.9-18.2% for spring 2020/21 while for fall 2020 it was between 9.3% to 12.0% on dry matter basis. For spring 2020/21, and fall 2019, the neutral detergent fiber and acid detergent fiber were below 50% and 35% respectively for all the farms but for fall 2020. In that fall the forage approached maturity at the time of grazing and feed quality of grazed cover crops declined on one farm with neutral detergent fiber and acid detergent fiber content as high as 65% and 36.3%, respectively. The farmers left 47-73% of standing cover crop biomass (1,368-5,992 lbs/A) for soil protection and soil health maintenance. Bulk density, aggregate stability, field saturated hydraulic conductivity, soil CO2 burst, organic matter content, and permanganate oxidizable carbon were not significantly impacted by grazing. This study shows that grazing cover crops can supply significant feed value to beef cows without detrimental effects for soil health, and it can therefore be an important component of sustainable intensification of cropping systems.
Source : psu.edu