Physiological and production responses of four grasses from the genera Urochloa and Megathyrsus to shade from Melia azedarach L.

This research investigated the effect of shade from Melia azedarach L. on the physiology, production, and forage quality of Megathyrsus maximus cv. Tanzania and cv. Mombaza, and the Urochloa hybrids Oaxaca and Yacar,. Evaluations were made during the rainy (August 2013) and windy (February 2014) seasons under sun and shade. Mombaza and Tanzania produced more forage biomass (4683 +/- A 4529 and 4279 +/- A 4745 kg DM ha(-1) harvest(-1); P < 0.05) than hybrids, and there was more biomass during the rainy (8236 +/- A 4257 kg DM ha(-1) harvest(-1); P < 0.0001) than the windy season, although biomass declined by 44 % (P < 0.05) under shade. Leaf crude protein was similar among grasses (P = 0.516), although Mombaza and Tanzania had higher neutral detergent (49.2 and 50.2 %, respectively; P < 0.05) and acid detergent fiber fractions (34.4 and 34.1 %, respectively; P < 0.05), making them less digestible (61.7 and 61.6 %, respectively; P < 0.05) than the hybrids. Overall, nutritional quality increased during the windy season (P < 0.05) and under shade (P < 0.05). Assimilation of CO2 was greater during the rainy season (P < 0.0001) and under sun (19.1 +/- A 8.2 vs. 8.6 +/- A 4.4 A mu mol m(-2) s(-1); P < 0.05). The most favorable conditions for biomass production occurred during the rainy season, although nutritional quality was better during the windy season. Shade affects photosynthetic rate and production, and promotes the nutritional quality of all grasses. Oaxaca and Yacar, appear to be more adapted to shade by responding with greater production stability and better forage nutritive quality.