Corn fertilizer management

Adequate fertilization management has proven to be essential to guarantee high productivity and economic return in corn cultivation, both in the summer and in the off-season. An adequate supply of nutrients must occur from the initial stages, when demand is high and the root system is still small, exploiting just a few centimeters of soil around newly emerged seedlings.

CRITICAL FACTORS

In the initial stages of corn development, the demand for nutrients is great and the root system is still small, exploiting just a few centimeters of soil around the newly emerged seedlings. The five-leaf stage is critical, as this is when floral differentiation begins (Fancelli & Dourado Neto, 1996), and it occurs very early, around three weeks after sowing. It is added that, of the total accumulated by corn, between 60% and 70% of the nitrogen and between 65% and 85% of the potassium are absorbed until flowering, which corresponds to half the duration of the crop cycle (Cantarella & Duarte, 2004 ). 

Fertilizers are preferably applied at sowing, due to the factors already mentioned. However, in the case of nitrogen, splitting during sowing and covering generally allows for greater efficiency in the use of the nutrient from the fertilizer, as at the time of covering, the root system is growing quickly and exploiting a greater volume of soil. Potassium is also divided into top dressing, to avoid possible saline effects, when NPK fertilizers are applied in the sowing furrow.

Omitting nitrogen during sowing and applying all the fertilizer in pre-sowing or covering, after plant emergence, can cause losses. In the summer harvest, Duarte & Cantarella (2005) found that the omission of nitrogen during sowing, compared to the dose of 60 kg/ha in the sowing furrow plus cover, reduced the productive potential of the crop and the efficiency of nitrogen fertilization ( Figure 2). In safrinha corn, the same effect was found by Duarte & Kappes (2016), in São Paulo and Mato Grosso, when studying the effect of top dressing, at the five to six leaf stage, in the presence and absence of 39 kg/ha of N at sowing (Figure 3). It should be noted that the majority of off-season corn in the central-west region is grown without nitrogen at sowing, applying it only as a cover crop. The simple anticipation of broadcast nitrogen fertilization, preferably at the time of sowing, can substantially increase the profitability of the crop in this region.

The anticipation of nitrogen fertilization that would be applied as cover on corn for the time of managing the species cultivated for straw production in autumn-winter has been practiced in some areas in a direct planting system with large accumulation of organic matter and straw, due to operational ease, as farmers have free time and machines at the end of winter. The argument is that the nitrogen applied to oats can be momentarily immobilized by the organic matter present in the system, especially by residues with a high C/N ratio, and become available for the corn crop later, as the factors that favor mineralization of the Nitrogen retained in the organic fraction – high temperature and humidity – are the same ones that promote corn growth. However, it presents risks of large losses of nitrogen through leaching and decreases in the use of fertilizer nitrogen and in grain productivity in years with high rainfall in the period prior to corn planting, as is common in summer.

The technique now being discussed is increasing the dose of nitrogen applied at sowing to improve plant starting. Nitrogen at sowing has gradually increased in Brazil, just as the first (or only) top dressing application has been made earlier and earlier. But, what is the maximum dose that can be applied when sowing? The answer depends mainly on the following factors: a) the method of applying the fertilizer when sowing - in the furrow or broadcast; b) spacing between lines; and c) soil texture. High doses applied in the sowing furrow can cause a saline effect and compromise the initial development of part of the plants and, in extreme cases, the stand. In general, the sum of the doses of N and K₂The amount of fertilizer in the sowing furrow should not exceed 80 kg/ha, especially if the formula also contains sulfate and/or the spacing between rows is between 80cm and 90cm (in reduced spacing, for example, 45cm to 50cm, the amount of fertilizer distributed per linear meter in the sowing furrow is smaller, as distribution occurs in a greater number of rows).

Leaching is greater in sandy soils than in clayey soils, increasing the risk of loss of nitrogen applied at sowing before absorption by the roots; the volume of soil explored by the roots is very small immediately after seedling emergence. In this case, most of the nitrogen must be applied in top dressing, in one or more times. When comparing the application of the total dose only at sowing with the application of 36 kg/ha of N at sowing plus nitrogen as cover, at the five-leaf stage, Duarte & Cantarella (2016) found that splitting was essential to obtain better yields. in Votuporanga (São Paulo), on sandy soil, but little effective in Mococa (São Paulo), in an environment with low productive potential and clayey soil (Figure 4).

It is important to mention that slow-release fertilizers are being developed for high-dose application at sowing, offering part of the nutrient immediately after application and part for a prolonged period of time, minimizing losses due to leaching.

The consolidation of direct sowing and two crops per year in the same area, together with improved soil fertility, allowed the adoption of system fertilization. In soils with corrected acidity and phosphorus and potassium levels above the critical level, fertilization recommendations are made per agricultural year, and not exclusively for each crop, using as a reference the replacement of nutrients exported by grains. It should be added that in most crops in the Chapadões of the Center-West, Maranhão and Tocantins, fertilizers containing NPKS are applied by broadcast. Due to the operational appeal, with short windows for carrying out soybean harvesting and off-season corn sowing operations, it is common to apply all phosphorus (and sometimes sulfur) in the pre-sowing of soybeans and only nitrogen and potassium on off-season corn.

The fertilization of systems should not be restricted to the criteria of nutrient balance and operational ease, even in soils with built fertility. Studies carried out by IAC and Fundação MT revealed the kick-start effect of phosphate fertilization on off-season corn, associated with nitrogen and/or sulfur, increasing its productivity, without harm to soybeans in succession, where phosphorus was no longer applied partially or completely. However, this effect is not evident in environments with very high phosphorus content (close to or greater than twice the critical level value) and/or production potential is limited (Figure 3).

Therefore, adequate fertilization management has proven to be essential to guarantee high productivity and economic return in corn cultivation in the summer and in the off-season.

Aildson Pereira Duarte and Heitor Cantarella, Agronomic Institute (IAC); Claudinei Kappes, MT Foundation

Article published in issue 213 of Cultivar Grandes Culturas.