If your crops are under stress by low temperatures, drought or too much rain, then a little help from in-season fertilizer could jump start their yields.
Several soil nutrients can be added at this time of the year, says Clain Jones, Montana State University soil fertility expert. "If soil nutrients are marginal, and root growth is slow due to cold or very wet conditions, then roots might not come into contact with a sufficient amount of nutrients," he says.
Foliar applications of micronutrient and immobile macronutrients such as phosphorus is most beneficial when added when there is enough leaf area to catch the liquid fertilizer, he adds. If immobile nutrient s land on the soil surface, they will likely not be readily available to the root zone.
Phosphorus is relatively immobile in soil and cold- or moisture-stressed crops' roots may not access sufficient amounts of this nutrient. If plants are dark green and stunted and older leaves are purplish, foliar phosphorus may be needed, says Jones.
Foliar phosphorus can be a good route to get phosphorus into stressed crops, he believes. Up to 16 pounds of foliar P205 per acre applied to wheat between early stem elongation and hear-heading may increase yields if plants are deficient, he adds.
"Applying foliar phosphorus later, near flowering, may increase yields due to delayed leaf senescence. But this only works, Jones warns, if there is minimal moisture stress, that is, in high yielding conditions.
Water-logged soils may actually have increased phosphorus availability. If soil phosphorus levels were adequate for average yields, additional phosphorus may not be needed for higher yield potentials regions of Montana that received heavy spring rains.
Cool and dry weather conditions are known to limit potassium availability. Potassium is important for nitrogen uptake, minimizing drought stress and speeding crop maturity. Potassium-deficient plants appear stunted with "burned" leaf edges, and potassium-deficient small grains may produce excessive tillering.