The adequate supply of nutrients to plants is a fundamental part of management in the search for high levels of productivity. And in the production systems of off-season corn and soybeans it is no different. Knowing the need and quantity required by plants is part of the list of essential measures for those looking to maximize the results of both crops.
It is essential to resume basing fertilizer recommendations on soil analysis results. Most of the time, fixed NPK, NK and NKS formulas or pre-defined raw materials are used throughout the property, only varying the doses. Although off-season corn is grown in “constructed fertility” areas, there is great variability in soil fertility between properties and plots.
In the Chapadões of central Brazil and borderline states, it is common to omit nitrogen when sowing with application of all fertilizers in top dressing. In these environments, It is recommended to carry out fertilization by broadcast sowing, in order to anticipate the application of fertilizers, which may or may not be complemented with a application of nitrogen in top dressing.
Off-season corn is defined as dry corn sown in the second harvest, in succession of crops. From 2012, it is the most important type of corn cultivation in Brazil. The culture predecessor is soybeans, in more than 95% of crops.
The use of waste crops and soybean fertilization is one of the main reasons for the success of corn safrinha, due to the need for less investment in fertilizer compared to corn summer. But, from the beginning of the development of appropriate technologies for this cultivation modality, it was evident that fertilizer residues previous ones were not enough to meet all the demand for nutrients in the beginning of plant development (Cantarella and Duarte,1995). Thus, the Farmers started using NPK fertilizers in the sowing furrows. At the However, with the evolution of the culture, the doses did not increase in a proportional to its productivity, not replacing all nutrient exports of off-season corn and/or the production system.
On the other hand, the fertilization process was adjusted to the reality of the new producing regions, especially the chapadões, applying broadcast fertilizers and the nutrient phosphorus only in soybeans. In most properties, the areas are very large, the soils are often very wet during the implementation of safrinha corn and the operational structures do not meet, without delay, due to the demand for the joint sowing and fertilization operation in the furrow. Prioritize yourself the use of agricultural implements that are easy to supply and have high operating income.
The first network experiments on fertilization of off-season corn were conducted by the Agronomic Institute (IAC), in the Médio Paranapanema region of São Paulo, from 1993 to 1995. It was found that splitting N with 10 kg/ha of N at sowing and remaining in coverage, old standard fertilization, could be increased to 30 kg/ha at sowing (Cantarella and Duarte, 1995). The use of 30 kg/ha of N during sowing, together with phosphorus and potassium in the sowing furrow (examples: NPK formulas 13-13-13, 16-16-16 and 16-18-14+S) avoids the uncertainty of whether or not there is moisture in the soil at the time that coverage with N should be provided, which could lead to deficiency in plants because they don't do it or because of their low efficiency.
Then, with the increase in productivity, earlier sowing and expansion of the safrinha corn cultivation area, it was found that to surpass the productivity of 6 t/ha it is essential to complement the sowing fertilizer with N in top dressing in doses compatible with the regime regional water supply and expected productivity. (Duarte et al., 2011).
In conditions It is not possible to predict the response of crops to nitrogen from of soil analysis. The fertilizer recommendation is made considering the history of crops in the area (in the case of safrinha corn, almost always soy), soil texture and nutrient demand by plants (extraction and export), estimated from productivity, and the results of crop response experiments to fertilizers.
Taking as a reference that the extraction and export of nutrients are proportional to grain productivity, which Bulletin 100 IAC (Table 1) recommends approximately 1 kg/ha of N per bag of corn produced per hectare, in environments with high nitrogen response (sandy soil and/or history of grasses). For conditions of lower response (consolidated direct planting system and legume history), the recommended amount of N can be reduced by more than 40%. For productivity of 9 tons per hectare of off-season corn, after soybeans in clayey soil, an export of 112 kg/ha is estimated and it is recommended 90 kg/ ha, that is, the use of 10 kg of N for each ton of corn, both per hectare.
Recommendations for N doses are carried out taking as a reference a source that presents losses due to volatilization despicable. However, urea is the most used source of N for application in coverage, due to the greater supply, lower price and ease of application and, when applied to the soil surface, N losses occur due to volatilization of ammonia, which can reach values close to or even greater than 40% of N applied. Therefore, it is necessary to increase the dose of N and/or mix it with urease inhibitors to compensate or minimize possible losses due to volatilization, since burying it in a furrow with simultaneous covering – which allows the control of losses due to NH3 volatilization – nor is always viable.
Some of the nitrogen needs to be mandatory applied at the time of sowing, as the absorption of nutrients occurs quickly during the first phases of the plant cycle of corn and the root system is still small, exploring just a few centimeters of soil around newly emerged seedlings. Doses are generally recommended from 30kg/ha to 40 kg/ha of N, which may be higher in broadcast applications. The maximum dose that can be applied in sowing depends mainly on the method of application fertilizer when sowing (furrow or broadcast); b), the spacing between lines and soil texture.
High doses applied to the sulcus sowing can cause saline effects and compromise initial development part of the plants and, in extreme cases, the stand. In general, the sum of the doses of N and K2O in the sowing furrow must not exceed 80 kg/ha, especially if the formula also contains sulfate and/or the spacing between lines are 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 there is distribution over a greater number of lines.
Leaching is greater in sandy soils than in clayey soils, increasing the risk of loss of nitrogen applied to the sowing before absorption by the roots. Thus, in safrinha corn crops implemented in soils of medium texture, it is very important to divide nitrogen in coverage.
The greater the proportion of crops sown at the end of January and beginning of February, during the rainy season, there is a greater chance of N losses through leaching due to water surpluses, with its installments for sowing and covering. On the other hand, top dressing may be ineffective in late sowing when carried out with dry soil and there is a delay until occurrence of rain.
Part of N is applied to coverage, up to the five-leaf stage, avoiding excess salts in the sowing furrow and, mainly, N losses due to nitrate leaching. Due to nitrogen losses through leaching in the soil profile, its installments in sowing and coverage generally allow for greater efficiency of use of the nutrient from the fertilizer, coinciding with the periods of greater demand for plants. Of the total accumulated by corn, between 60% and 70% of the nitrogen and between 65% and 85% of the potassium are absorbed until the flourishing (Cantarella & Duarte, 2004).
In safrinha corn, the installment of the nitrogen in more than one coverage is recommended only in situations special, since the total dose is relatively low, less than 100 kg/ ha, in most crops, with at least 30 kg/ha of N already used in sowing. A quality of distribution of low doses of fertilizers to be broadcast in an area total is one of the critical points of carrying out more than one fertilization of coverage on off-season corn.
In the Chapadões of central Brazil it is nitrogen is often omitted during sowing with application of the entire top dressing fertilizer. Duarte & Kappes (2015), when studying the effect of top dressing fertilization in São Paulo and Mato Grosso, in the five to six stage leaves, in the presence and absence of 39 kg/ha of N at sowing, found that the omission of nitrogen during sowing reduced the productive potential of the crop and the nitrogen fertilization efficiency. (Figures 1 and 2). They also verified that there was no difference in the productivity of the corn when N was applied in the furrow or broadcast for nitrogen fertilizer applied alone or associated with P or PS. Therefore, if there is a limitation to carrying out fertilization in furrows when sowing, instead of just doing the covering fertilization, broadcast fertilization can be carried out, without interfere with the sowing operation. Just anticipate the application of the fertilizers, which may or may not be complemented with an application of released nitrogen.
Potassium and nitrogen are the nutrients most accumulated by the aerial part of corn, but potassium presents the highest proportion of accumulation in the initial stages, in relation to the total accumulated. Karlen et al. (1987) found that corn plants accumulated 60%, 46% and 80% of the total N, P and K absorbed throughout the cycle. Results Similar results were recently obtained by Bender et al. (2013)
Potassium has been divided into cover on summer corn, to avoid possible saline effect, when NPK fertilizers are applied to the sowing furrow. But in the case of corn off-season, when the recommended doses are relatively low, its Application can only be made in the sowing furrow. In the case of crops with fertilization exclusively by broadcast, considering that potassium is the nutrient accumulated in greater quantities in the initial stages of development of corn plants, its application alone or in NPK formulas, such as 20-00-20, should be carried out as soon as possible.
If there is not adequate moisture in the soil so that the potassium applied to the surface moves along the profile of the soil in a short space of time and is absorbed by the roots, the effect of this fertilization on crop productivity may be negligible or null. One of the options is to prioritize the application of potassium in soybean crops and reduce doses in off-season corn.
When planning fertilization, do not should consider only corn, but the succession of corn and soybean crops. In soils with corrected acidity and phosphorus and potassium levels above the level critical (constructed fertility soils), the fertilization recommendation can be made per agricultural year, and not exclusively for each crop, using as reference to the replacement of nutrients exported by grains.
However, system fertilization is not should be restricted exclusively to the criteria of nutrient balance and operational ease, even on soils with built fertility. In most of Chapadões crops it is common to apply all the phosphorus (and sometimes sulfur) released before soybean sowing and only nitrogen and potassium in corn safrinha. In this case, the nutritional balance of the system is positive, but it remains of applying phosphorus to off-season corn.
Studies carried out by IAC and Fundação MT revealed the kick-start effect of phosphate fertilizer on corn safrinha, associated with nitrogen and sulfur, increasing its productivity, without damage to soybeans in succession, where phosphorus was no longer applied partially or completely (Figures 1, 2 and 3). The association of P and PS with nitrogen, compared to application exclusive to N, provided the highest values of productivity and/or gains efficiency of nitrogen top dressing, expressed in quantity of corn per unit of N applied. This effect occurred both in broadcast fertilization as in the sowing furrow. However, it was not so evident in environments with high very high phosphorus level (close to or greater than twice the value of the critical), highlighting the importance of using soil analysis results for your recommendation.
The ideal when adopting the system fertilization is that phosphorus is applied to the safrinha corn and supplemented when sowing soybeans, except in soils with very high phosphor. By using nutrients and appropriate dosages in off-season corn, these will also be available in the system for soybeans, which will be sown in October and November, improving the profitability and performance of crops in the system.
In the same study, there was also a low frequency of response to potassium in the safrinha corn, despite its high accumulation in the aerial part of the plant. Thus, in clayey soils, with high potassium content, flat and without stains, the application of potassium from the safrinha corn crop and apply the amount exported by corn together with potassium from soybeans, with all application made to soybeans. In In other situations, K should not be omitted from corn.
By Aildson Pereira Duarte, Heitor Cantarella, IAC; Claudinei Kappes, MT Foundation
Article published in issue 226 of Cultivar Grandes Culturas, March, 2018.
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