Effect of sward type and level of light on the agronomic performance and nutritive value of Panicum maximum var. Trichoglume and Stylosanthes humilis

Abstract

Silvopastoral systems have great importance in tropical countries and it may be expected that pasture-based systems in deforested areas of the humid tropics will move towards to tree-pasture or tree-pasture-crop systems in the future. Plant performance depends directly on the available light as it provides the energy needed for photosynthesis and also canopy shading from trees may influence plant productivity. A study was conducted to investigate agronomic performance, competitive ability and nutritive value of grass (Panicum maximum var. Trichoglume) and legume (Stylosanthes humilis) in pure swards and in a mixed sward under two different light levels (full sunlight & 30% of full sunlight). The experimental design was a 3 (P. maximum pure sward, S. humilis pure sward and P. maximum and S. humilis mixed sward.) x 2 (100% light, 30% of light) factorial experiment arranged in a randomized block design with 3 replicates.

Dry matter accumulation of both P. maximum var. Trichoglume and S. humilis in pure swards out yielded mixed sward due to its higher sward production, (leaf area, higher no of tillers, and no.of unfolded leaves). However, the relative yield of grass (RYG=O.707) is greater than 0.5 indicating that there was an advantage for grass grown in a mixed sward as compared with a pure swards. While the relative yield of legume (0.53) is very close to 0.5 indicating no advantage for legume in a mixed sward. Therefore it could be suggested that the dry matter accumulation of P. maximum var. Trichoglume was not affected (P>0.05) by the shade, probably due to its higher leaf area as well as low net assimilation rate. Higher leaf area under the shade which has compensated the dry matter accumulation. In contrast, higher dry matter accumulation and CP content of S. humilis (P<0.05) in full sun light as compared with the plants grown under the shade, confirm that S. humilis is less shade tolerant than the green panic and requires high irradiation for successful growth.

Crude protein concentration of P. maximum was significantly low (P<0.05) in full sunlight. This is attributed to the fact that, CP concentration in plant tissues becomes diluted as a result of high dry matter accumulation. Low CP concentration of S. humilis would have been due to the adverse effect of shade on nodulation and nitrogen fixation. In addition, higher dry matter digestibility of P. maximum grown in a mixed sward as compared with pure wards indicates that the grasses in a mixed sward were less mature than the grasses grown in a pure sward especially when irradiation is not a limiting factor for growth. Dry matter digestibility of S. humilis was slightly higher in pure sward as compared to the mixed swards.

Finally, P. maximum var. Trichoglume could be considered as a shade tolerant grass even due to its high yield and quality under the shade. However, S. humilis could not be recommended as a suitable companion to be grown in a mixed sward with P. maximum var Trichoglume due to the adverse effect of shade on its yield and quality. Therefore further investigations are needed to find out shade tolerant legumes to be grown in mix sward with P. maximum.