Production and nutritive value of silage corn in different reproductive stages

— Corn has been the most used crop for whole plant silage, due to its high potential for dry matter production, high energy and great adaptability to different growing regions. Due to the great importance of the culture for this purpose, the region of the Far West of Santa Catarina, due to the presence of one of the largest dairy basins in Brazil, demands the supply of this food to the animals mainly during the season of forage. Thus, the objective of this work was to evaluate different hybrids and to identify the optimal corn cutting time for silage production that provides a greater economic return to the system. The experimental design used was a randomized complete block design in a 2x4 factorial scheme, allocating different maize hybrids (P30F53 VYHR®; P32R48 VYHR®) to the main plot and the reproductive stages (R2, R3, R4, R5). The experiment had 8 treatments and 3 replicates, totaling 24 experimental units. The studied variables were: dry matter content (DM); crude protein (PB); acid detergent insoluble fiber (FDA); neutral detergent insoluble fiber (NDF); total digestible nutrients (NDT), and CNF-amido, at the reproductive stages. The best economic yield is obtained when the maize crop is ensiled at the reproductive stage R4 and R5. Among the hybrids, the P32R48 VYHR® was the one that obtained better yield, providing greater production of milk by área.


I. INTRODUCTION
The importance of dairy monoculture in the state of Santa Catarina is indisputable, both as a source of income for rural properties, as for the generations of jobs in the processing industries. Currently, the state is the fourth largest milk producer in the country, with 2.83 billion liters of milk, with emphasis on the western region of Catarinense, which represents 79% of this production (EPAGRI/CEPA, 2018). To maintain this growth, producers constantly seek, forms of supply the nutritional demands of their herds, with quality pastures, supply of concentrated feedingstuffs or preserved foods (silage or hay). In this sense, it gains prominent role, the making of corn silage plant. Due to food shortages during certain periods of the year, when the forage used as the basis for feeding livestock, cannot meet the nutritional demands. Maize has been the most used crop for making plant silage whole due to its high potential for dry matter production and its large adaptability to different cultivation regions (FACTORI et al., 2012). Still, there is a large number of maize hybrids destined for silage production, from which significant differences with respect to the production of Green forester, production of grains, leaves and stalk directly interfering with the nutritional value of the silage (MORAES et al., 2013). In this sense, the choice of hybrid and reproductive stage of cutting becomes determinant factors for the success of the system, since the hybrid may represent up to 50% of the final yield (FACTORI et al., 2012), and the stage of cutting that the plant is in, is directly related to the available energy of this material, by increasing the participation of grains (MARAFON et al., 2015). In this context, it is important studies, which demonstrate the best strategy for harvesting these hybrids, which provide higher milk production ha-1 and economic income for the rural producer. In this way, the objective of this work was to evaluate different hybrids and identify the ideal moment of cutting of maize for silage production that provides greater economic return to the system.. The base fertilization used was 520 kg ha-1 of the fertilizer MAP (11-52-00), the pre-planting fertilization (21 days before sowing) was 800 kg per hectare of potassium chloride 00-00-60, and in the fertilization of coverage were used 320 kg per hectare of the fertilizer nitrogenated urea (45-00-00), at V4 Stage, and 480 kg per hectare of Sulfammo MeTA® (29-00-00), in the V6 stadium.

II. MATERIALS AND METHODS
The hybrids used were the Pioneer brand, P30F53 VYHR® and P32R48 VYHR®, both with Leptra® technology (maize cartridge caterpillar, Spodoptera Frugiperda) and RR (Roundup Ready®), with industrial seed treatment (Dermacor® + Poncho® + Derosal Plus®). Weed control was performed 20 days after sowing of the crop with a herbicide based on Atrazine + Simazine (Primatop® 6, L ha-1). As soon as the culture reached the stages of R2, R3, R4 and R5, the cuttings of the whole plants were performed in the useful area of each plot and at the cutting height of 25 cm, in order to achieve maximum milk production per hectare, considering beyond the quality of the ensiled mass, also a larger amount of stored dry mass. The cut in the aforementioned reproductive stages, aim to represent the different harvesting points observed in the region of study, where most farmers, because they are family farmers, depend on the outsourcing of the service of harvest. In this way, some crops occur when maize is in the R2 stage (anticipating the harvest), or in R5, due to the high demand of farmers for this type of service. On the other hand, the producers with better implement structure, which can perform the harvesting when they deem appropriate, perform the cut normally when the plants are in R4. The samples were packaged in mini PVC silos with 75 mm in diameter and 50 cm in height. After 30 days of Data were subjected to analysis of variance by the F test using the statistical software sratgraphics (12.5). When the data did not present interactions among the factors (hybrids and reproductive stages of cutting), were analyzed as simple effects. The averages that showed significance were compared by the Tukey test (P < 0.05). .

III. RESULTS AND DISCUSSION
The interaction between the factors (hybrids and reproductive stages of cutting) was not significant (P < 0.05) in the variables studied, and the isolated effect of each factor was analyzed, as can be seen in table 2 and 3. For the hybrid maize factor, there was no significant effect for the variables MV, MS and PB. However, there was a difference (P < 0.05) between the response variables, starch, NDT, NDF and FDA (table 2). Observing the data presented in table 2, it is noted that the hybrids used in the experiment, because they are of double aptitude (grain and silage), have qualitative and quantitative characteristics within the expected standard for a good quality silage. As shown in Figure 1, one of the factors responsible for this result was the good climatic conditions, recorded during the development of the culture.
The production of 84.51 and 87.70 Mg of MV ha-1 in the hybrids analyzed were much higher, the production above 55 Mg of MV ha-1 considered by Neumann et al., (2015), as characteristic ideas of a good hybrids. This high production per hectare, in addition to allowing greater production of meat or milk per area, still dilutes the production costs. There was no difference between the crude protein values between the hybrids and neither between the different reproductive stages (table 2 and 4). COSTA et al., (2006) considers that PB contents below 7% could be limiting animal production, because they imply less voluntary consumption, reduction in digestibility and negative nitrogen balance. However, it is observed that the silages produced in this work (table 2 and 4) would satisfactorily meet (PB ≥ 7,81) to the minimum requirements of ruminants. On the other hand, in the case of milk production, the PB contents would be limiting the productivity, since the NDT values could provide conditions to obtain higher production values.
In the different reproductive stages of cutting, there was a significant statistical difference (P < 0.05) for the variables MV, DM, starch, NDT, FDN and FDA, with no difference between treatments only for the variable PB (table 3).  Cabral et al., (2012) The higher the proportion of grains in the mass, the higher the values of total digestible nutrients found. Therefore, besides the total mass production, it should also be considered the quality of the silage, which is influenced by the proportion of the plant components and the advancement of the reproductive stage of the plant. Thus, despite the increase in the fraction in more advanced stages of maturation, the increase in grain participation, provides higher energy levels and the quality of silage in greater proportion, than the losses caused by the fibrous portion (Oliveira, 2010), a situation observed in this work. The FDN and FDA values (table 3) decrease with the advancement of the reproductive stages, this result is due to the greater participation of grain in silage, consequently higher energy value (starch) and higher nutrient content digestible (NDT). Ensiled crops, before the ideal point, besides presenting lower total mass production, have a higher NDF content due to the occurrence of effluent and the lower share of the grain fraction in the mass ( VAN SOEST, 1994;VILELA et al. 2008). Similarly, Marafon et al. (2015), evaluating different maize harvesting stages, observed that maize plants in the R5 stage presented lower FDN and FDA content, when compared to the R3 stage due to the dilution of these fractions, by the transformation of simple sugars into starch in the grain component. Also, VAN SOEST et al., (1991), points out that good silage must comply with some minimum quality criteria.
Thus, values lower than 50% of neutral detergent fiber and 32% of acid detergent fiber (table 4), are important because they have a high correlation with the capacity of daily dry matter consumption and energy density of the resulting silage, respectively (VAN SOEST et al., (1991). For the production estimate (L cow-1 day-1; L ha-1), a significant isolated effect was verified between the hybrids and between the reproductive stages of cutting. Thus, the production estimate was higher for the hybrid P32R48 VYHR®, with values of 15.43 L cow-1 day-1, 16900.4 L ha-1, while the P30F53 VYHR®, obtained an average yield of 14, 47 L Vaca-1 day-1, 15845.7 L ha-1 (table 4). Averages followed by the same letter in the column do not differ from each other (P < 0.05) by the Tukey test. Standard error of Mean ± (0.299 L cow-1 day-1), and ± (327.69 L ha-1).
The highest production observed in hybrid P32R48 VYHR®, possibly due to the fact that it has a higher MS content, which raises the amount of PB available (table  2), approximately 90 kg of PB more per hectare, even if it does not differ from the other treatment. According to Pereira et al., (2007), the MS and PB contents of the plant are important factors in the ensilage process and in the determination of the nutritional value. This hypothesis may be considered because the protein in this case is the limiting factor of production, therefore greater availability of PB, higher production. In addition to being highly demanding in energy, lactating animals also present high protein demand that can limit the productive potential of these animals. The protein content in the diet has a positive correlation with the consumption, being this effect partly from the increase in   (table 7). In relation to the economic performance of the different reproductive stages, the R5 and R4 are superior to the other treatments, with no difference between the same (Table 7). Averages followed by the same letter in the column do not differ from each other (P < 0.05) by the Tukey test. Standard error of mean ± (631.918).
It can be seen that when the harvest of corn for whole plant silage was performed at the R2 stage, although it provides the producer with the removal of the early crop of the crop and allows to anticipate the sowing of the second crop, the producer fails to win, R$9353.11 Ha-1 when compared to the cut performed in R5. It is also important to emphasize that the ensilage process can be done between the R4 stages and R5 without significantly compromising the economic performance of the system, since the difference between these two cutting moments (R4 and R5) is only R$198.285 ha-1. This result is important as it allows a longer interval of time for the producer to perform the harvesting and ensiling of the material, decreasing the disorder and financial losses to the system.