Soil organic carbon and aggregation under poplar based agroforestry system in relation to tree age and soil type Naveen Gupta S. S. Kukal S. S. Bawa G. S. Dhaliwal Received: 14 August 2008 / Accepted: 23 February 2009 / Published online: 5 March 2009 Ó Springer Science+Business Media B.V. 2009 Abstract The poplar based agroforestry system improves aggregation of soil through huge amounts of organic matter in the form of leaf biomass. The extent of improvement may be affected by the age of the poplar trees and the soil type. The surface and subsurface soil samples from agroforestry and adjoin- ing non-agroforestry sites with different years of poplar plantation (1, 3 and 6 years) and varying soil textures (loamy sand and sandy clay) were analyzed for soil organic carbon, its sequestration and aggre- gate size distribution. The average soil organic carbon increased from 0.36 in sole crop to 0.66% in agroforestry soils. The increase was higher in loamy sand than sandy clay. The soil organic carbon increased with increase in tree age. The soils under agroforestry had 2.9–4.8 Mg ha -1 higher soil organic carbon than in sole crop. The poplar trees could sequester higher soil organic carbon in 0–30 cm profile during the first year of their plantation (6.07 Mg ha -1 year -1 ) than the subsequent years (1.95–2.63 Mg ha -1 year -1 ). The sandy clay could sequester higher carbon (2.85 Mg ha -1 year -1 ) than in loamy sand (2.32 Mg ha -1 year -1 ). The mean weight diameter (MWD) of soil aggregates increased by 3.2, 7.3 and 13.3 times in soils with 1, 3 and 6 years plantation, respectively from that in sole crop. The increase in MWD with agroforestry was higher in loamy sand than sandy clay soil. The water stable aggregates (WSA [ 0.25 mm) increased by 14.4, 32.6 and 56.9 times in soils with 1, 3 and 6 years plantation, respectively, from that in sole crop. The WSA [ 0.25 mm were 6.02 times higher in loamy sand and 2.2 times in sandy clay than in sole crop soils. Keywords Aggregation  Agroforestry  Carbon sequestration  Soil organic carbon  Tree age Introduction Agroforestry, growing of multipurpose trees along with agricultural crops is one of the key paths towards the prosperity of poor people suffering from hunger, malnutrition, abject poverty and deterioration of the environment in the areas that have been bypassed by the Green revolution (Garrity 2004). Agroforestry is believed to increase the soil organic carbon (SOC) through litter fall (Young 1989), check soil erosion (Escobar et al. 2002; Schultz et al. 2004), increase land productivity (Noble et al. 1998) and diversify the farm income (Seobi et al. 2005). Presence of trees within a landscape affects its hydrological characteristics (Pereira 1979), just as deforestation increases the run-off (Lal 1981). Agroforestry is thus the most viable option to tackle land degradation and to bring about N. Gupta  S. S. Kukal (&)  S. S. Bawa  G. S. Dhaliwal Department of Soils, Punjab Agricultural University, Ludhiana, India e-mail: sskukal@rediffmail.com 123 Agroforest Syst (2009) 76:27–35 DOI 10.1007/s10457-009-9219-9