Tree growth and nutrient status of soil in a poplar (Populus deltoides Bartr.)-based agroforestry system in Punjab, India

Poplar (Populus deltoides Bartr.) based agroforestry systems are economically viable and more sustainable than many other crop rotations prevalent in northern India. Growth {girth at breast height (GBH) and height} and productivity (volume) of clone G-48 of poplar spaced at 5 x 4 m, soil organic carbon (OC), and concentration of available macronutrients (N, P and K) and micronutrients (Zn, Fe, Mn and Cu) in surface soil (0-15 cm depth) were determined at an interval of six months starting from April 2002 till October 2003 in one and four year old (in January 2002) 16 poplar plantations on farmers' fields in Ludhiana, Punjab. The observations were taken from plantations having fodder {sorghum (Sorghum bicolor)/pearlmillet (Pennisetum americanum) in summer}-wheat (Triticum aestivum) (in winter) rotation throughout the poplar age and those having sugarcane (Sachharum officinarum) initially during two years and fodder-wheat rotation thereafter. The GBH, height and volume of younger plantations intercropped with fodder-wheat rotation were 15.6, 17.2 and 46.7%, respectively higher than that of plantations intercropped with sugarcane. Growth increment of poplar was markedly higher during April to October than October to April. Soil OC was significantly greater in older (6.83 g kg-1) than the younger (5.35 g kg-1) plantations. Available macronutrients in soil increased at successive sampling times. The average Zn concentration at final sampling was 17% lower compared to initial sampling, whereas the other micronutrients tended to increase during April 2002 to October 2003 and the increase was higher in four year old plantations than one year due to higher inputs of organic matter.