Climate change has modified the behavior of climate variables, for this reason, pastures manifest a seasonal productive behavior, where the deposition of structural carbohydrates is modified and in some cases the absorption of minerals. The objective of this study was to characterize, in varieties of Cenchrus purpureus tolerant to drought, the chemical composition of leaves and stems at different ages of regrowth in conditions of intense seasonal drought. The experimental period covered the years 2013 to 2015, in the Experimental Station of Pastures and Forages of the Institute of Agricultural Research “Jorge Dimitrov”. In a completely randomized design with the factorial arrangement was used, and the dynamics of the chemical composition of leaves and stems of new varieties of C. purpureus were characterized, in different ages of regrowth and different climatic periods (rainy and not very rainy), and their combination (4 x 3 x 2). The interaction age of regrowth with climatic station affected the chemical composition of the leaves (p≤0.001), altering the content of cellulose (Cel), hemicellulose (Hcel), neutral detergent fiber (NDF), acid detergent fiber (ADF), cellular content (CC), calcium (Ca) and silica (Si), while in the stems this interaction only affected the concentration of ADF. The isolated effect of the climatic season modified in leaves (p≤0.01) the content of phosphorus (P) and lignin (Lig), it stems the P content (p≤0.001). When the regrowth age varied, there was a modification of the chemical composition of the leaves (crude protein and Lig) and stems (crude protein). The new varieties of C. purpureus under conditions of degradation and intense seasonal drought showed a pattern of chemical behavior similar to that of tropical grasses, but with low contents of protein and phosphorus.

Keywords: cell walls, grasses, carbohydrates, feed crops, dietary fibers.