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Fluid Journal : Fluid Journal 1993-1995
Winter 1995 40-year loss (bu/A) 40-year loss ($/A)1 Crop 1 Assumes 20 ton/A/year soil loss over 40 years = 6 inches/40 years 260 240 220 200 180 160 140 120 1,200 1,000 800 600 400 200 Wheat Sorghum Soybeans Figure 2. Influence of topsoil erosion on cumulative yield and profit loss, Havlin et al., 1994. Table 1. Water-use efficiency, conventional vs. conservation-till. Bu/A of rain USA avg. 3.5 Conventional-till 5.0 Conservation-till 7.0 High yielder 11.0 0-3" "ABC" Soil Probe 3-12" 12-24" A B C and soybeans grown on five Kansas soils over six years. Results indicated that grain yields significantly decreased with decreasing topsoil depth (Figure 1). Yield losses as high as 2 bu/A per inch of topsoil lost resulted. Profit losses were as high as $51/A in the first 6 inches of topsoil eroded. Data in Figure 1 can be used to project the cumulative yield and profit loss associated with long-term soil erosion. Let's assume that 6 inches of topsoil eroded over 40 years, representing an annual soil loss of 0.15 inches/A/year (Figure 2). As can be seen, using 1990 market prices with deficiency payments, cumulative profit loss over a 40-year span could run as high as $1,027/A. These cumulative profit losses are similar to current land prices in Kansas, thus, if soil erosion had not occurred the pro- ducer would have had sufficient revenue to pay for the land. Water management Water frequently limits crop yield potential, which is especially true as we move from the Midwest to the Great Plains. Unfortunately, water management is seldom the highest management priority, ranking behind variety selection and fertility. After water, fertility and pests usually become the next most yield- limiting factors. Growers are reducing water runoff and evaporation, and increasing water infiltration by maintaining surface crop residue cover (reducing tillage intensity). The water loss reductions and increased infiltration are essential to increasing stored soil water. Reduced-till systems almost always improve water-use efficiency (Table 1). Evaluating the different sources of plant-available water is important in understanding where the investment in water conservation provides the greatest return. Water stored in the soil profile is potentially 100 percent available to the next crop. Therefore, any soil profile water left after harvest must not be lost. The major losses of stored water during non-crop periods occur through weed growth and evaporation from the soil. The amount of rain that infiltrates the soil greatly increases with standing residue. Rain falling on a bare soil, for example, can seal off the soil surface within 30 minutes. As little as 0.5 inch of rainfall can seal the surface of a bare soil. Once sealed, infiltration slows or ceases and water begins to run off. Surface residue cover can increase the time for infiltration by two- or threefold, greatly reducing runoff and soil loss by erosion. Nutrient management Soil testing. Obtaining profitable crop yields, minimizing water- and nutrient-use efficiency, and minimizing environmental impacts of nutrient use require regular soil testing. Soil testing is the best method available to accurately determine nutrient availability and provide a guideline for optimum fertilization. Soil sampling under reduced-till presents a special problem that should be addressed. Since the land is no longer mixed with a moldboard plow, nutrient stratification can occur (Table 2). Thus, immobile elements such as phosphorus, potassium, and zinc may concentrate Figure 3. ABC method of sampling.
Fluid Journal 1996-1998