Cover cropping and conservation tillage improve soil health in the southeastern United States

Abstract

Conservation agricultural systems have a long history of development and use in the southeastern United States, but they are still not the norm on the landscape. Literature from the region suggests that a diversity of soil properties can be improved with cover cropping and conservation tillage, but results are not always consistent. Our objectives were to (a) review recent research on conservation tillage and cover cropping in the region and (b) compile and synthesize recent data from a diversity of farms along a conventional to conservation gradient. As part of recent on‐farm trials focused on soil N availability, we analyzed soil organic C and N fractions and routine soil nutrient characteristics from a total of 196 fields in corn (Zea mays L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) production in three physiographic regions of the Coastal Plain (n = 71 fields), Piedmont (n = 77 fields), and Appalachians (n = 48 fields) in North Carolina, South Carolina, Pennsylvania, and Virginia. These data allowed us to establish first estimates of threshold optima for soil organic C and N fractions and other inorganic nutrients. On‐farm data confirmed the literature review that conservation tillage resulted in greater stratification of soil organic C and N and nutrient concentrations. Soil health improvement could be inferred along the gradient from inversion tillage to no tillage without cover cropping to no tillage with cover cropping. This collection of recent literature and on‐farm data can be a useful starting point for establishing target limits and assessing soil health conditions on farms in the region.

Adjusting the N fertilizer factor based on soil health as indicated by soil‐test biological activity

“…Knowing the stable association between STBA and mineralizable soil N (Farmaha et al., 2022), it should now be possible to adjust the N fertilizer factor to field‐specific conditions and not rely solely on regional or statewide averages. However, the economically optimum N fertilizer level depends not only on satisfying plant N demand, but also on the cost‐to‐value threshold (CVT) of fertilizer and agricultural products.…”

“…Soil‐test biological activity (STBA) is a standardized short‐term soil respiration protocol used in the Soil Ecology and Management Lab at North Carolina State University that is a simpler and less expensive indicator of the more complex biological process of mineralizable soil N, which along with mineralizable carbon (C) varies substantially depending on historical management (Franzluebbers et al., 2018; Franzluebbers & Pershing, 2020; Pehim‐Limbu & Franzluebbers, 2022). Across a diversity of fields in North Carolina, South Carolina, and Virginia, a strong linear association occurred between STBA and mineralizable soil N (Farmaha et al., 2022). This association reflects the consumption of organic resources by soil microorganisms, with CO 2 emitted and N mineralized to ammonium and nitrate, providing growing plants with inorganic N. However, mineralization is dependent on suitable environmental conditions over time.…”

“…The Soil Ecology and Management Lab is a research laboratory that has developed this understanding and application of soil testing technology through varied collaborations. Categories of STBA were synthesized to those indicated in Figure 1 based on recent experience with a diversity of field conditions (i.e., 158 corn trials, 92 tall fescue trials, and 38 small grain trials in the Carolinas and Virginia; Farmaha et al., 2022) to understand the N cycling function. Categories may need to shift when estimating different soil functions, such as for water partitioning or biodiversity enhancement, and these calibrations remain to be developed.…”

Effects of Soil Conservation Management Systems on Soil Enzyme Activities under Wheat Cultivation

“…Applying minimum tillage and cover crops, which are within the conservation soil practices, has positive effects on soil properties such as increasing soil organic matter, soil nitrogen, soil phosphorus, soil aggregation, soil microbial activity, soil porosity and decreasing soil compaction, runoff and water erosion [9,10]. In addition, the integrated use of cover crops and conservation soil tillage systems increases their positive effects on soil properties [11].…”

“…In recent years, studies researching soil enzymes have been manifold. Some of these were done on the effect of organic materials applied to the soil [8,12], some soil tillage systems [13][14][15], some fertilization applications [16][17] some cover crops or different mulch materials [10,[18][19][20][21] on the enzyme activity, while very few of them were carried out in the form of double or triple combinations [7,9,22]. In this study, the enzyme activity was investigated in a semi-arid region, which can be considered problematic (pH 8.5), the application of 3 different cover crops after the main product of wheat (which has no practical application in the region) at 3 different soil depths of two different tillage (traditional and minimum) systems (0-10, 10-20, 20-30 cm).…”