Conservation Tillage Systems in the Southeast

Conservation Tillage Trade-Offs

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While conservation tillage can significantly enhance infiltration, there are trade-offs. The benefits of conservation tillage will vary depending on the crop being grown, soil characteristics, topography, surface cover, pest pressure, agrichemical use and weather. Normal agricultural practices such as spraying, planting and harvesting can lead to soil compaction. This is particularly true for soils with high clay contents. With conventional tillage practices this surface compaction is periodically disrupted. With reduced tillage, the compaction can build up over time and can actually lead to a reduction in infiltration. As a consequence, strip-till and other conservation tillage practices can lead to increased runoff and increased agrichemical and nutrient losses [7, 8, 12]. In high clay content soils, tillage may be required to alleviate soil compaction. In part, the compaction can be reduced through strip tillage [9] and through in-row subsoiling or paratilling [11, 15, 16]. Paratilling is a deep tillage technique in which the soil is loosened below the soil surface but not inverted [10]. Compaction can also be alleviated by certain deep-rooting cover crops, including some cereal grains and radishes.

The increased infiltration typically observed with conservation tillage can lead to increased subsurface water loss because infiltration amounts can exceed the soil’s capacity to hold water. Many soils in the southeastern United States have subsurface layers that have lower hydraulic conductivity and restrict vertical percolation of water. This restriction can lead to saturated zones within the soil profile. Water within these zones will flow downslope away from cropped fields. Some of the infiltrated water also moves through the root zone and into subsurface aquifers. Driven by hydraulic gradients, this water also moves downslope away from the fields. If soils under conservation tillage become compacted and have a reduced capacity to hold water, total water losses can equal or exceed the total water losses typically observed with conventional tillage systems. In this case, water remaining in the soil profile when using strip-tillage may not contribute to an overall water gain for crop use and can potentially increase agrichemical and nutrient loss by increasing subsurface water flow [1].

Although there are disadvantages in some situations, the advantages of conservation tillage systems outweigh the disadvantages associated with soil compaction and increased subsurface water losses. Conservation tillage can lead to reduced erosion and increased infiltration. When used in conjunction with cover crops during the non-growing season, conservation tillage can also lead to increases in soil carbon. Some carbon from plant materials is returned to the soil through decomposition. Plants that leave higher residue levels can lead to greater soil carbon levels. Soils with higher carbon levels hold more nutrients, have improved water-holding capacity and exhibit better soil aggregation (see Chapter 3). Cover crops have the added advantage of enhancing infiltration and reducing soil erosion. Optimizing the biomass produced by the cover crop will yield the greatest benefits.

A reduced-tillage plan can be targeted to specific soil, land slope and crop production needs. Care must be taken to monitor soil compaction and periodic steps must be taken to alleviate the compaction (see Chapter 6). In addition, because of the potential for increased subsurface losses, attention must be paid to the management of soluble chemicals, particularly nitrate. Manage fertilization to minimize these losses by applying only what is needed for crop growth. Use split applications timed to meet crop needs and use cover crops to scavenge leftover nitrogen.

Download the tables from Chapter 14.