Search

This study assessed the nitrogen nutrition index, morphogenic characteristics and tiller structure of Alexandergrass (Urochloaplantaginea (LINK) Hitch) pasture submitted to different nitrogen (N) levels (zero, 150 or 300 kg ha-1 of N). The experimental design was entirely randomized with repeated measures arrangement. The experimental animals were Angus heifers under rotational stocking grazing method. The number of animals was variable to keep 30±5 cm post-grazing sward height. Nitrogen nutrition index increased linearly according N levels (Ŷ = 59.8 + 0.1216N; P < 0.0001; r²=0.53). The leaf appearance rate adjusted to a positive linear regression model according the thermal sum (TS) with zero of N (Ŷ0N = 0.0077 + 0.0000087TS; P = 0.0308; r² = 0.72) and 150 kg ha-1 of N (Ŷ150N = 0.0020 + 0.000021 TS; P = 0.0022; r² = 0.92). The use of 300 kg ha-1 of N did not alter the leaf appearance rate (0.0124 leaf degree-days-1). The use of up to 300 kg ha-1 of N increases the Alexandergrass nitrogen content. The leaf appearance rate in Alexandergrass is modified using N while the morphogenic characteristics leaf expansion, stem expansion, phyllochron, leaf lifespan, leaf elongation duration and tiller structure are not altered by N utilization. RESUMO: Este trabalho teve como objetivo avaliar o índice de nutrição nitrogenada, as características morfogênicas e a estrutura dos perfilhos de papuã (Urochloa plantaginea (LINK) Hitch) submetidos a diferentes níveis de nitrogênio (N) (zero, 150 ou 300 kg ha-1 de N). O delineamento experimental foi inteiramente casualizado com medidas repetidas no tempo. Os animais experimentais foram novilhas Angus em regime de pastejo rotacionado. O número de animais foi variável para manter 30 ± 5 cm de altura do pasto pós-pastejo. O índice de nutrição com nitrogênio aumentou linearmente de acordo com os níveis de N (Ŷ = 59,8 + 0,1216N; P < 0,0001; r² = 0,53). A taxa de aparecimento de folhas ajustou-se ao modelo de regressão linear positiva de acordo com a soma térmica (TS) com zero de N (Ŷ0N = 0,0077 + 0,0000087TS; P = 0,0308; r² = 0,72) e 150 kg ha-1 de N (Ŷ150N = 0,0020 +0,000021 TS; P = 0,0022; r² = 0,92). O uso de 300 kg ha-1 de N não alterou a taxa de aparecimento de folhas (0,0124 folha grau-dia-1). O uso de até 300 kg ha-1 de N aumenta o teor de nitrogênio do papuã. A taxa de aparecimento de folhas em papuã é modificada usando N, enquanto que as características morfogênicas expansão foliar, expansão de colmo, filocrono, duração de vida das folhas, duração da elongação foliar e a estrutura dos perfilhos não são alteradas pela utilização de N.

This study evaluated the effect of rice straw supplementation on cow-calf systems and the effect of increasing stocking rates on bio-economic efficiency. Three production systems were compared in which pregnant females were supplemented with different levels of rice straw in the prepartum: 1) 20 cows in 9 hectares (ha) of natural pasture without rice straw supplementation and stocking rate of 1,000 kg of body weight (BW)/ha (RSH0); 2) 30 cows in 13.5 ha of natural pasture receiving 5 kg of rice straw/animal/day and 1,000 kg BW/ha stocking (RSH5); and 3) 60 cows in 14 ha of natural pasture with 10 kg of rice straw/animal/day and stocking rate of 2,000 kg BW/ha (RSH10). The body condition score (BCS), cow weight at calving (CWC), and calf birth weight (CBW) were recorded on the first day and every 30 days. After calving, cows were moved to oat pasture (Avena strigosa) and ryegrass (Lolium multiflorum) with mineral supplementation where BW and BCS were evaluated every 30 days, and a transrectal ultrasound was performed every 15 days to determine the interval of parturition ovulation (IPO). Cows were separated in two groups and a fixed-time artificial insemination was performed (d130 and d165), followed 61 days of natural mating (d140-d175) and a gestation diagnosis 30 days after natural breeding (d231-d266) to verify the pregnancy rate (PR). Data comparison was performed by SPSS and productivity and gross margin (GM) were analyzed. We observed no difference in BCS between the beginning of prepartum until the parturition, nor in CWC, BW, IPO, and PR. The productivity and GM of RSH10 were 44.2 and 40.2% higher than RSH0 and 46.8 and 45% higher than RSH5, respectively. Thus, rice straw in the final third of gestation for cows in natural pasture allows the maintenance of cow's productive and reproductive parameters, as well as increased productivity while intensifying the system.