Effect of tree density on productivity of a Prosopis cineraria agroforestry system in North Western India

An experiment was initiated in 1991 to evaluate crop productivity and define optimum tree density with advancing age of Prosopis cineraria (L.) (Khezri) in an agroforestry system. Plots of P. cineraria at densities of 417 (D1), 278 (D2) and 208 trees/ha (D3) were intercropped with Vigna radiata (L.) (mungbean) in 1995, 1997, 1999 and 2000 with Pennisetum glaucum (L.) R. Br. (pearlmillet) in 1998 and 2001. Tree height and collar diameter increased by 2.5 and 2.2-fold in D1, 2.2 and 2.4-fold in D2 and 2.2 and 2.0-fold in D3 plot, respectively in the 6-year period. The highest crop yields were found in D2 plots in 1995 and 1996, in D3 plots in 2000 and in the control plots in 2001. The lowest crop yields were found in D1 plots throughout the duration of the experiment. Trees produced utilizable biomass of 19.1, 15.8 and 10.3 tones/ha and dry leaf weight of 0.85, 0.67 and 0.50 tones/ha, respectively in the D3, D2 and D1 plots at the age of 12 years (June 2002). Low soil water content at 1 m distance from tree base compared to that at the center of four trees indicated greater utilization of soil water within the tree rooting zone. The yield of the annual crop increased when density of P. cineraria was appropriate (i.e., optimum tree density). But optimum tree density varied with tree size/age due to competition for soil resources. Yield of the annual crops was the highest at optimum tree densities of 278 trees/ha (4 m×9 m) at 6 and 7 years, 208 trees/ha (8 m×6 m) at 10 year and <208 trees/ha at 11 years of age. The study indicated greater benefits of P. cineraria tree integrated at optimum density through tree produced and synergistic effects on the annual crops.