Farmers often struggle to manage fertilizer expenses.
They have a lot to consider. The dynamic nature of soils, as well as differences in soil testing labs, recommendations, application methods, and crop goals all complicate the decision making process.
The dilemma often lies somewhere between what the soils lab recommends and what the grower can afford to put into a crop. However, after water, fertility is generally the next limiting factor to obtaining yield goals.
We recently concluded the Coastal Bend Soil Sampling Campaign and presented the sample results and recommendations to participating growers. The program received 124 soil samples representing over 19,000 acres. Residual nitrogen levels found in submitted soil samples ranged from a low of 2 parts per million (PPM) to a high of 46 ppm, highlighting the varying fertility levels in our area. The difference between those two fertility levels in terms of available nitrogen is about 90 pounds per acre. Given those dramatic differences, soil fertility testing must be the basis of any fertility management decisions made by growers.
However, not all soils labs run the same test, use the same nutrient requirements, or have the same philosophy behind their recommendations. Soils labs like AgriLife Extension’s take the approach of providing what a crop needs to meet a yield goal for a given year based on the current soil nutrient status. Other labs encourage a build and maintain strategy, providing ample nutrition to the crop yet preventing luxury consumption. Both philosophies have merit. Growers should be aware of the recommendation strategy behind the lab they choose and make sure it is in line with their production goals.
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Farmers should base yield goals on realistic projections of crop potential. While the overall goal is to move the bar higher in terms of yield, the ultimate goal is to maximize profitability. Field records for individual fields provide the best insight for yield potential. The estimated average county yields for the past 10 years are around 3,700 and 650 pounds per acre for grain sorghum and cotton, respectively. Granted, precipitation has hampered production; however, this only emphasizes the need to set realistic yield goals when obtaining fertility recommendations.
Additional savings may be found by crediting fields for residual nitrogen deeper in the root zone. A recent trial in grain sorghum found residual nitrogen levels of 204 pounds per acre by soil sampling to a 2-foot depth in one field in Victoria County. At 70 cents a pound that’s over $140 per acre worth of nitrogen sitting in that field! While levels that high are exceptional, since 1998, on more than 55 sites sampled to a 48-inch depth, 33 have had an excess of 100 pounds of available nitrogen.
A final cost saving measure to reduce phosphorous application requirements is to consider banding. Phosphorous applied in a band is more efficient that broadcasting because the calcium carbonates in our soils bind or “fix” most of the phosphorus into calcium phosphate when it is broadcast. Recommended phosphorous fertilizer rates can be reduced by 40 percent to 50 percent if banded using a 4-inch by 4- inch to a 6-inch by 6-inch placement from the seed.
Farmers can reduce fertilizer cost significantly by following any or all the above suggested practices. However, all are ultimately based on a good soil test to identify current soil fertility levels that will help producers from making a budget cut that could affect yield potential and profitability. For more information on fertility management you can contact the Nueces County Extension office at 361.767.5223.