Corn cultivars for silage

Although the corn ensiling technique is well known, the definition of which hybrid will be adopted in a given location, the property's technological package, adequate crop management and a production and conservation process are important to obtain the expected yield.

Corn cultivation is an important source of food for the production of milk, meat and derivatives. Widely adapted to different climatic conditions, it is part of a large part of agricultural production systems. In addition to the grains produced by the cereal, its use in making silage from the aerial part of the plant, at the appropriate time, contributes to increases in cattle production rates, especially in dairy farming. Periods of scarcity of bulky food caused by prolonged lack of precipitation and low growth of native pastures are the most demanding times for preserved alternative foods, produced in other periods.

Although there are several species of annual or perennial forage agricultural plants that can be used for roughage production, corn is the most commonly used crop. Characteristics such as green matter yield, fermentation quality, maintenance of the nutritional value of the food after its stabilization, acceptance by animals, low buffering power, dry matter content greater than 30% and palatability make corn silage the most used by producers in feeding animals.

Although the corn ensiling technique is well known, the definition of which hybrid will be adopted in a given location, the property's technological package, adequate crop management and a production and conservation process are important to obtain the expected yield. Furthermore, the technique can and should be adjusted for each property, thus allowing greater process efficiency.

TECHNOLOGY IN THE SEED

The seed is one of the fundamental components in the success of the production process, which is why it is necessary to choose the most appropriate form of the hybrid to be sown. Characteristics such as productive potential, resistance to pests and diseases, adaptation to the production system, adaptability to soil and climate conditions are essential for the crop to become more competitive.

According to the National Supply Company (Conab), for the 2013/14 harvest, 467 corn cultivars were offered, of which 253 transgenic cultivars and 214 conventional cultivars. This large supply of hybrids with new biotechnological advents has enabled resistance and/or tolerance to certain foliar diseases, lepidopteran pests (caterpillars) and specific herbicides, which has contributed to more rational management of the crop, making it have greater productive potential. . Another key point in the seed technology segment is the genetic base used (single, triple, double hybrids and open pollinated varieties) (Figure 1). Currently, with changes in the dynamics of breeding programs, simple hybrids dominate the corn seed market. These genotypes are highly demanding on favorable cultivation, management, fertility, water precipitation and sunlight conditions to be able to express their productive potential.

The texture of the grain influences the quality of the roughage, changing its energy value and reducing the need for concentrated feed. There are basically two types of grain texture and their transitions in the seed market: Dent-type grains (zea mays ssp. Indentata) and Flint-type grains (zea mays ssp. Indenduro) (Figure 1). Dent-type grains have a soft, floury, porous starch that is easy to enzymatically attack and has a low density due to the loss of moisture in the grain. This central region of the grain “shrinks” giving it a toothed shape. Hard type grains (flint) have, as the name suggests, hard or crystalline endosperm occupying almost their entire volume, with a low proportion of mealy endosperm. This vitreousness in hard grains is defined by the proportion of hard endosperm (vitreous) in relation to the total endosperm, reducing susceptibility to enzymatic hydrolysis, decreasing its digestibility of the carbohydrate present. However, it must be considered that from the management of the hybrid x texture, both textures can be adequately used to make silage.

Currently, there is a greater supply of seeds with a hard texture in the seed trade, with exceptions for the southern region of Brazil, where seeds of the toothed type are still offered. One of the reasons for this greater presence may be the increased grain production that this type of texture provides.

SPATIAL DISTRIBUTION OF PLANTS

The improvement of the development environment for the corn plant allowed the use of higher population densities along with the modification in the spatial distribution of plants. This methodology is associated with genetic improvement and more specific management, providing plants with more erect leaf architecture, smaller plants with smaller spike insertions and less shading of the lower leaves, thus providing greater use of the insolation incident on the plants, and/or for improvements in cultural management of the crop with better use of irrigation and fertilization technologies.

The spatial distribution of plants in Brazil is still very varied (Ritchie et al., 2003), where variations in row spacing from 0,35m to 1,20m and population densities of 35 thousand plants/ha to 100 thousand plants/ha are observed. This variation is related to cultivation characteristics, the technology used, available phytosanitary management and the purchasing power of producers. Increases in the distribution and sometimes density of plants are one of the easiest and most efficient alternatives for increasing productivity through better use of productive resources (Demétrio et al., 2008). The increase in plant density must be adjusted for each hybrid x location x environment, in order to maximize local resources.

Reducing the spacing between rows is also an alternative to provide increases in productivity (Penariol et al., 2003). With smaller row spacings, up to a certain limit, grain productivity increases through better use of water and light. The partition of dry matter exported via silage comes from 90% through the fixation of atmospheric elements through the process of photosynthesis (Ueno et al., 2011). Therefore, maximizing strategies that can increase the use of environmental resources becomes an important strategy to improve silage yield. As a result, the light falls on the lower leaves for longer, the plant is less stressed and these leaves remain active for longer, and can be used for the silage process. If there is intense competition within the sowing row, the plants will prioritize the youngest leaves and the oldest (lowest) leaves will senesce earlier and consequently the cutting height will be greater and there will be a lower silage production per area.

NUTRITIONAL REQUIREMENT OF THE CROP

The planning of a given area for silage must take into account the nutritional requirements of the crop, production ceiling and export of dry matter and consequently nutrients. Therefore, the most exported nutrients are nitrogen (N) and potassium (K). When a corn crop is ensiled and stored in a silo, the integrity of the minerals in the aerial part of the harvested plant is renewed, unlike when only the grains are removed.

According to Coelho (2006), silage production of approximately 18 tons of dry matter exports 230 kg/ha of nitrogen and 265 kg/ha of potassium. For Oeno et al. (2011) this amount of nutrients removed by the aerial part causes damage to the nutrient balance and rapid impoverishment of the soil, resulting in a drop in productivity and low quality of silage in subsequent crops when not constantly subjected to replacement of these mineral elements through analyzes of soil. According to Cruz et al. (2010), for this system it is necessary to increase the base saturation to 70% and the K content to 5% of the soil's cation exchange capacity. Furthermore, fertilization must be carried out at the ideal time for the development of the crop for silage production, in which the components of the plant's green mass (leaves and stem) in addition to the grains, are also important. In general, for these systems higher doses of 30% to 50% are used when compared to grain production and must be carried out in at least two covering fertilizations in which in the first application (four to five leaves) around 30% of the top dressing. This limited quantity is sufficient to expand/prepare the root system for the second application, as well as helping to define the productive potential for higher ceilings. The second application (approximately 70%) must be carried out after greater formation of the corn plant's root system, thus reducing the possibilities of nitrogen losses or lack of coverage of the root system when absorbing nutrients. The second top dressing application of nitrogen is recommended when the plant has 7 to 8 leaves.

CUTTING MOMENT

The harvest point is another very important factor in the success of this activity, directly affecting the quality and productivity of the crop in the ensiling process. Its determination recommends maximum dry matter yield and the best nutritional quality of the plant, resulting in contents between 30% and 35% DM in its constitution.

This moment is characterized when the plant has a milk line visible on the grains, that is, 2/3 of the endosperm is hard and 1/3 is still soft. This phase comprises, on the phenological scale of the crop, R4 and R5, approximately 35 days to 45 days after the flowering of the crop. For Nussio and Manzano (1999), these DM levels are obtained in corn plants at a time when the consistency of the grains is varying between the pasty and hard mealy stages, which corresponds to the visualization of the milk line.

According to Cruz et al. (2008), harvesting corn with DM levels above 35% to 37% is not desirable, as they increase the resistance of the silage mass to compaction. But in contrast, higher moisture contents of the material are related to lower DM production, losses due to leaching of compounds, low final quality of the roughage and reduced consumption by animals. For Dermachi (2001), the moisture value of the material should be concentrated between 65% and 70% moisture, as values ​​below and above this range indicate losses due to effluents and fermentation of the material.

The cutting height is normally between 25cm and 30cm above the ground, but may change depending on the phytosanitary conditions of the lower leaves of the plant. According to Dias (2002), increasing the cutting height at the time of ensiling results in a reduction in the stalk/cob ratio, which leads to improvements in the nutritional characteristics of the roughage.

Final density is a characteristic greatly affected by the correct choice of harvesting time, as it is directly related to particle size, very dependent on the mechanical implement used and DM content. This affects the porosity of the roughage, which establishes the aeration rate of the silage material, and subsequently, its degree of deterioration during storage and desilage (Bolsen & Bolsen, 2004). An ideal density for good silage is located between 550 kg/m^-3 at 700 kg/m^-3, as values ​​much higher than this are not recommended, as they generally result from silages with lower dry matter contents, harvested greener or with poor compaction.

FORAGE QUALITY

At the end of the fermentation and storage process, it is expected to obtain a material with high quality, good acceptability by animals and no loss due to deterioration. Average values ​​most found in the literature emphasize that a good silage is one that has 30% to 35% DM, 5,8% to 7,5% crude protein, 23% to 28% acid detergent fiber, 38% to 43% neutral detergent fiber with total digestible nutrients above 68%.

The quality of silage is directly related to numerous factors already described previously, but it is always linked to the yield of the crop to be used in the production of roughage. Hybrids with good grain yields or MS at the silage point do not always have the best qualities for animal production, more specifically milk production.

In the seed market scenario, there are several specific hybrids for grain production, others more intended for animal production, and those considered to have dual aptitude. In work carried out in the 2014/15 harvest in the central region of Rio Grande do Sul, evaluating five specific corn hybrids, a spatial distribution was found, determining the specificity of each genetic material tested.

The yield components of the evaluated corn hybrids are presented in Table 1.

This greater response is directly associated with fewer losses in its production cycle caused by insect pests and their genetics, giving it greater yield with greater health. Using a methodology proposed by the University of Wisconsin (MILK 1997 - Undersander et al., 1993), based on a numerical modeling system that takes into account the pre-established parameters of a standard animal, we have: cow body mass: 509 kg; cow milk production 18,9 L/d; percentage of fat in milk 3,42%; intermediate lactation stage; percentage of losses in silage of 10%, and neutral detergent fiber of silage 49,44% and digestibility “vitro” of dry matter 67,9%. From the input parameters of the different hybrids, the possible milk production per area is obtained. With this, corn hybrids can be characterized in terms of their suitability. By having grain production and milk production per area, it is possible to combine these two pieces of information and obtain a graph with four distinct areas. Hybrids located in region A are more suitable for milk production, region B indicated for dual suitability and in region D for grain production. However, these comparisons are only valid if the contrasting hybrids are considered for the evaluations as well as the production environment, as each hybrid has a complexity of options for its development.

The higher the quality and quantity of roughage produced, the less will be the need for supplementation of this food. Therefore, it is possible to achieve high production rates with reduced costs, whether in the dairy chain or in meat production. The animal's productive response provides the best way to determine the quality of the roughage produced.

Other items must still be considered for the production of quality silage, such as the type of silo, particle size, the use of equipment capable of reducing particle size, sealing and conservation time before opening the silo.

Thomas Newton Martin, Paulo Eugênio Schaeffer, Thânia Maria Müller, Alex TagliaPietra Schönnell, UFSM

Article published in issue 207 of Cultivar Grandes Culturas.