Produtividade e qualidade da forragem e do feno de capim tifton 85 adubado com N e colhido em duas idades de rebrota / Productivity and quality of forage and hay of Tifton 85 grass fertilized with N and harvested at two ages of regrowth

Loreno Egidio Taffarel

Three experiments were conducted with Tifton 85 grass. The first objective was to evaluate the structural characteristics and bromatological composition of forage under effect of different doses of nitrogen (0, 25, 50, 75 and 100 kg N ha-1 in each cut) and two ages of regrowth (28 and 35 days). The experimental design was a randomized block design with 5x2 factorial arrangement and four replications, and each cut harvest was analyzed independently. It was observed a greater length of stem, leaf size and rate of elongation and the increase in crude protein and lower content fiber in acid detergent and lignin with increasing dose of nitrogen. The greater efficiency of N use, considering the four cuts occurred in the 100 kg N ha-1 at the age of 35 days of regrowth (13.79 kg DM kg-1 of N). O N promoted higher content of crude protein (CP) at the age of 28 days, and happened the highest concentration in the fourth cut (208.2 g kg-1 DM) and lowest in the second cut (140.12 g kg-1 DM); there were no differences between ages in the concentration of mineral matter and acid detergent fiber (ADF). The variation of rainfall exceeding 200 mm between December 2010 and March 2011, influenced the production of MS and, consequently, the total output of nutrients. The second study aimed at assessing the effects on the bromatological composition of the hay in the steps of cut, baling and 30 days after stored under the five levels of nitrogen (N). The experimental design was randomized blocks in factorial scheme 3x5 (3 steps haying and 5 doses of N), with two cuts harvested for each age of regrowth (28 and 35 days) and for each age was carried out two types of drying hay: dried in field under the sun and in shed, in the shade. Analyses were performed separately for each cut, age and form of drying. It was observed increase in acid detergent indigestible protein (ADIP) after 30 days of storage, the levels of acid detergent fiber increased between 6 and 35% after storage, and the largest increases occurred in the hay dried in the shade; the crude protein (CP) varied according to each cut, but increased as a function of N levels. In absolute terms, there was a greater difference in CP content (less than 31 g kg-1 DM) and neutral detergent fiber (+58.4 g kg-1 DM) between the cut steps and 30 days storage in the dried hay shade. This suggests that is important for better quality hay, a quick drying process for the production of hay. The third study aimed to estimate the curves of dehydration, the occurrence of fungi and mycotoxins in Tifton 85 hay dried in the field under the sun and shade (in two cuts and regrowth ages of 28 and 35 days for each form of dehydration) . The experimental design was 5x4 to drying in the sun 5x12 and for drying in the shed, four sampling times (0, 8, 23 and 32 hours) for drying in the sun and twelve sampling times (0, 3, 18, 27, 42, 51, 66, 75, 90, 99, 114 and 123 hours) for drying in shed (in shade), both with five N rates and four replications, with turn over and scatter made by hand daily. For identification of fungi, we used the 5x3 randomized experimental design, five doses of N and three steps of haymaking (cutting, baling and storage of 30 days), with four replications for each age of regrowth and drying forms.Samples were seeded with forage article size of 5 mm on PDA culture medium and after growth were identified with the help of specific identification keys and with the aid of microscopy. To verify the presence of mycotoxins were collected 20 composite samples (each composite sample were from the four replicates of each dose of nitrogen) hay stored for 30 days, with 10 coming from hay dried in the sun and 10 from hay dried in shed. To produce hay with sun-dried fodder was necessary 32 hours of dehydration, water loss rates were greater than 6.10 g g-1 h-1 DM in the first 8 hours after cutting and average loss of water approached 2.0 g g-1 h-1 MS. For dehydrated fodder in the shed, it took 123 hours, with a rate of dehydration below 0.5 g g-1 h-1 for MS due to environmental conditions. There was a predominance of three genera of fungi: Fusarium, Penicillium and Aspergillus. The largest population was Fusarium, followed by Penicillium in the steps of baling and storage. The mycotoxin fumonisin were found in higher concentrations and there was no difference (p>0.05) in the concentration of fumonisin in the hay dried in the sun (90 μg kg-1) and in the shed (60 μg kg-1). Although there is a low risk to animal health, occurred a higher production of aflatoxins (5,38 μg kg-1) and zearalenone (79,89 μg kg-1) in hay dried in the sun, indicating that the diurnal x nocturnal temperature variation with still high moisture of the material in hay favored the production of mycotoxins and that we must produce hay in a favorable environment, how the rapid dehydration and turning and spreading after harvest to inhibit the production of mycotoxins above permissible levels

Produtividade e qualidade da forragem e do feno de capim tifton 85 adubado com N e colhido em duas idades de rebrota / Productivity and quality of forage and hay of Tifton 85 grass fertilized with N and harvested at two ages of regrowth

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