Soil testing critical after a drought year
Furrow-irrigated fields generally will have larger amounts of water applied per irrigation event, which can result in nitrate leaching below the root zone, depending on how irrigation was managed. Expect residual nitrate-N levels to be quite low for furrow-irrigated fields. However, variability in residual nitrate can be very high with furrow irrigation. It will be critical to sample residual nitrate from the upper, middle, and lower third of the field relative to the location of irrigation pipe, since more leaching will occur in the upper third of the field.
Phosphorus, Potassium, and Other Nutrients
For irrigated fields with yields close to normal, expect little impact from drought on soil test levels of phosphorus (P), potassium (K), and other nutrients. For dryland fields, crop uptake of these nutrients will be less than normal. However, this may have little impact on soil test levels for P, K, and other nutrients. There may be some tendency toward higher soil test values, but soil tests for these nutrients are an estimate of plant availability over the growing season. There is evidence that soil test K can be influenced by soil drying, and some states have started analyzing soil K from field moist samples. However, most Nebraska soils are quite high in potassium, and thus slight differences in soil test K that can occur with the analytical process have no impact on the fertilizer recommendation.
Silage and Residue Harvest
In many cases, growers harvested fields intended for grain production as silage. In other cases, there will be opportunity to harvest crop residue as feed due to reduced pasture and hay production. Either way, growers should be aware of nutrient removal resulting from biomass harvest. Significant amounts of P, K, and micronutrients, as well as carbon, can be removed from the field with biomass harvest. For example, a 150 bu/ac corn crop will uptake approximately 64 lb P205 and 42 lb K2O in grain, but will have approximately 36 lb P205 and 144 lb K2O/acre in stover. The value of these nutrients should be considered when pricing baled stalks for livestock feed. More information on the impacts of harvesting crop residues is available in the Extension publications Baling Corn Residue (EC711) and Harvesting Crop Residues (G1846). If stalks are grazed rather than baled, expect much of the nutrient content in grazed residues to return to the field, minus the harvested weight of cattle once they are taken off the field.
The Bottom Line