Fertilizers contribute incisively to the final production. To develop optimal fertilizer recommendations, it is necessary to determine the status of plant-available nutrients. The right fertilizer doses avoid incurring saline stress or nutritional deficiencies that lead to yield losses.
What elements should growers consider besides the results of a soil test?
The chemical-physical analysis of the soil is only a starting point to accurately establish the nutrient requirements of plant growth. Growers need to evaluate irrigation, crop rotation and soil organic matter content, which strongly influences the optimum fertilizer doses, especially when it comes to nitrogen uptake.
In confirmation of this, the University of Wisconsin provided the recommended annual nitrogen uptake, based on these characteristics, compared to the potential yield.
These values should be amended depending on the crop residues before planting corn: when they cover at least 50% of the soil, it is advisable to increase the nitrogen inputs by 30% to facilitate the mineralization of the organic matter. If the previous crop is a legume, this addition is not necessary.
Also, regarding P and K, the fertilizer inputs vary according to the potential yield and soil nutrients content.
In this case, the irrigation also affects the recommendations: generally, it is sufficient to increase the dose by 20% in irrigated land.
Tips on nutrient management planning to maximize yield
Once the nutrient requirement has been defined, it is essential to study the rates and timing of fertilizer applications. If the wrong rates or timing are chosen, then stress, deficiencies and leaching losses of nutrients—especially nitrogen—may occur even if the nutrient requirements were adequately determined.
According to the guidelines of the University of Pennsylvania, 50-90% of N uptake must be distributed as a sidedress when the plant is 10 to 20 inches tall. Generally, this occurs after about 30 days from emergence when there is the maximum requirement of N. This way, the distributed nitrogen is not subject to leaching and denitrification, which reduces the efficiency of fertilization and damages the environment.
From the graphs, we see how important it is to identify the right timing for fertilizer application in order to avoid a situation where the crop doesn’t have N during the most demanding phenological phases.
Recent studies led by the University of Wisconsin have shown that the adoption of this strategy has led to higher yields in almost all types of soil, but especially in sandy and irrigated ones.
Furthermore, in some cases, the use of ammonium-based N starter, which has an inhibiting effect of denitrification, distributed in pre-planting has improved the grain yield. Despite this, ammonium is toxic to the roots so it is advisable to use ammonium phosphate, which provides K and has a low concentration of ammonium. Ammonium-based formulations must always be positioned 2 inches away from the seeds.
However, the use of N starter in pre-planting is not a stringent standard to obtain higher yields, as effectiveness depends on the characteristics of the soil, as shown in the study carried out by University of Wisconsin.
Regarding P and K, an increase in yields was found in many tests using P20 and K20 based starters in pre-planting, even in soils where the nutrients content was already high. The positive response to the starters was more frequent (50-60%) when the sum of the hybrid RM and date of the planting is 240-250, while less frequent (40-50%) when the sum is between 220-230.
In general, to obtain yield improvements, the ideal is to make minimum doses of complete starters (10 + 20 + 20 N, P2O and K2O), both in soils that have low nutrients content and in those with good ones, but not in soils with excess.