Respostas de forrageiras tropicais submetidas a doses de calcário e fósforo

Abstract

The aim of this study was to evaluate the effect of phosphorus and lime rates on forage production, morphogenetic and structural characteristics of 12 forage plants of Panicum maximum and Brachiaria spp. The evaluations were divided into two experiments in a greenhouse. Experiment 1 was conducted in a randomized block design in a 6x5 factorial scheme, with six Brachiaria spp. Marandu, Mulato II, BRS Ybaté, Basilisk, HD4 and HD1 and five doses of phosphorus (P) of 0, 13, 26, 52 and 104 mg dm-³, equivalent to doses per hectare of 0, 50, 100, 200 and 400 kg, respectively, with four repetitions. Experiment 2 was conducted in a randomized block design in a 6x2x5 factorial scheme, with six forage plants of Panicum maximum Tamani, PM422, PM408, Zuri, PM414 and PM406, two doses of P (P19 and P116 mg dm-3) and five doses of limestone (0, 326, 653, 1306 and 2612 mg dm־³) with three replications. The Panicum were established in two groups to facilitate the understanding of the answers, the first of small size (Tamani, PM422 and PM408) and the second of medium size (Zuri, PM414 and PM406). The forages were grouped according to their similar values in height of growth in pots of cultivars launched on the market BRS Tamani and BRS Zuri. To evaluate dry mass production (DMP), five cuts were made every 28 days, except the first one, which was 58 days after sowing. Morphogenesis evaluations such as appearance rate (LAR), leaf elongation rate (LER), leaf life span (LLS), stem elongation rate (SER), final leaf length (FLL) and number of leaves live (GNL), were performed every 21 days and the tiller population density (TPD) before each cut. After the last cut, the roots were washed in sieves, dried and weighed to determine the dry mass of roots (DMR; g pot-1 of DM). In experiment 1, DMP showed a positive linear behavior with increasing doses of P (P=0.0001). Higher LAR and similar in function of forage of 0.13 cm tiller-1 day were observed in Basilisk, HD4 and HD1 (P<0.0001). Higher LER of 4.04 and 3.87 cm tiller-1 day was observed in BRS Ybaté and Marandu, respectively (P=0.0006), the same forages had higher values of FLL (19.72 and 18.46 cm tiller-1 day, respectively). Linear increasing responses as a function of P doses were observed for LER, LLS, SER, FLL (P<0.0001, P<0.0001, P=0.0003 and P<0.0001, respectively) and quadratic behavior for GNL (P<0.0001). Higher TPD (45 tillers) was observed for HD1 receiving 104 mg dm-3 P (P<0.0001). The highest DMR were found in Mulato II and Marandu (20 and 21.80 g pot-1, respectively) (P=0.0004), however, Mulato II was superior despite much smaller amounts when compared to the highest dose of P. In experiment 2, for low-sized Panicum maximum there was an increase in DMP due to the phosphorus*lime interaction (P=0.0384), an increasing linear response was observed for lime doses associated with P116 mg dm-3, with a higher value of 15.08 g vase-1 at the dose of 2612 mg dm-3 of limestone. The supply of P promoted changes in LAR, LER and SER, higher values were observed in P19. When analyzing the effect of forages, a higher LAR of 0.11 day was for PM422, for LER higher values were for PM422 and Tamani (4.11 and 3.79 cm tiller-1 day, respectively), and for FLL higher values were observed in PM422 and Tamani (19.12 and 18.00 cm tiller-1 day, respectively). Higher TPD in the phosphorus*lime interaction of 71.08 tillers was observed at the dose P116 mg dm-3 associated with 2612 mg dm-3 limestone, lower values (mean= 23 tillers) (P=0.8124) were observed at the dose P19 associated with limestone doses. When the forage*phosphorus interaction was analyzed, higher values of 29.66 and 74.53 tillers (P19 and P116 mg dm-3, respectively) were observed in PM408. Higher DMR of 27.84 g pot-1 was observed at the dose of P116 mg dm-3. For medium-sized Panicum maximum, there was an increase in DMP due to forage, phosphorus and limestone (P=0.0059, P<0.0001 and P<0.0001, respectively). Higher DMP as a function of forage of 11.09 g pot-1 was verified in Zuri, as a function of P the highest value of 15.93 g pot-1 was at the dose P116 mg dm-3, and for limestone a quadratic response was verified with higher values at doses ≥ 653 mg dm-3 of limestone. As for LAR and SER (P<0.0001 and P=0.0069, respectively) the result was inversely proportional to the increasing P doses. Forage, were observed in Zuri and PM406, respectively. For FLL, a higher value of 25.38 and 22.70 cm was observed in Zuri and PM406, respectively (P<0.0001). The highest LLS of 59.70 days was observed in PM414 (P<0.0001), as a function of P, the highest value of 56.76 days was observed in P116 mg dm-3 (P=0.0017). The highest TPD of 31 tillers in the forage*phosphorus*limestone interaction (P=0.0032) was observed for PM406 receiving the P116 dose, associated with a dose of 2612 mg dm-3 of limestone. The highest DMR in the forage*phosphorus interaction of 34.73 g pot-1 was observed for PM406 receiving the P116 dose (P<0.0001). Phosphate fertilization promotes increases in forage production and root mass in Brachiaria spp. and Panicum maximum. Marandu and BRS Ybaté had higher LER and FLL, the variables directly influencing forage production. Basilisk, HD4 and HD1 were highlighted in the tillering. Results in experiment 2 prove that the application of lime enhances forage production, as phosphorus availability increases. PM422 tends to have longer sheet length. PM406 seems to respond more to soil fertility increments, and PM414 is perhaps more adapted to soils with low P availability. However, more studies in the field, and with grazing pressure, are needed to continue evaluations of forages in the phase pre-release.

KEYWORDS: Brachiaria, limestone, phosphate fertilization, dry mass, morphogenesis, Panicum.