Biomass production and root distribution pattern of selected fast growing multi-purpose tree species

Abstract

A randomized block design experiment involving nine fast growing multi – purpose trees (Acacia auriculiformis A. Cunn. ex Benth., Casuarina equisetifolia J.R. & G Forst., Leucaena leucocephala (Lamk.) de wit. Var. K 8, Ailanthus triphysa (Dennst.) Alston, Emblica officinalis Gaertn, Artocarpus heterophyllus Lamk., Pterocarpus marsupium Roxb., Paraserianthes falcataria (L.) Neilson and Artocarpus hirsutus Lamk.) Initiated during June, 1985 was used for the present investigations. The objectives of the study included quantifying the biomass production potential of nine selected fast growing multi-purpose tree species grown under short rotation intensive cultural systems; characterising the root distribution pattern of these trees and also elucidating the extent of nutrient loss through harvest, besides characterising litter dynamics. Acacia and paraserianthes recorded the highest growth rates in terms of height, radial growth and biomass yield. Biomass production decreased in the order: Acacia > Paraserianthes > Casuarina > A. heterophullus > Emblica Pterocarpus > A. hisrsutus > Ailanthus > Leucaena. The most important component of total biomass undoubtedly, was the bole while foliage contributed least to biomass yield. Nevertheless foliage, in general registered the highest N, and K contents. Among the species, Leucaena had the highest N concentration followed by Paraserianthes and Pterocarpus. For P and K concentrations, Pterocarpus and A. hirsutus registered the highest concentration. A one – to – one correspondence between nutrient accumulation and biomass yield was however, lacking because of wide variations in elemental concentrations among species and also among tissue types. Bole fractions, in general, did not account for more than 50 % of total nutrient export from site. Altering the rate of nutrient removal in products is one of the most important design criteria in planning for sustainable plantion. N-fixing tree plots generally had a higher soil N status. Casuarina, Emblica and Pterocarpus plots were having higher P levels. Acacia, Paraserianthes and A. hisrsutus plots registered markedly higher K level. The amount of litterfall was maximum for Acacia and the minimum for Pterocarpus. Litterfall also followed a unimodal distribution pattern with a distinct peak during the November – January period and the period of lean fall was during May-August. Litter dynamics accounted for bulk of the nutrient inputs into the system. The retranslocation of mineral nutrients from senescing leaves to younger leaves and /or other tissues prior to abscission was obvious. Leucaena, Paraserianthes, Pterocarpus, Acacia, Alinathus and Emblica formed examples of high (> 1.5%) detrital N content. Generally the wet period (June – August) was characterised by increased concentration of N in litter. Litter P did not follow a consistent pattern with respect to seasons. However, a characteristic decline in litter K concentration was noticed during the rainy season. Mass disappearance of litter samples followed a negative expontential relationship. Leucaena litter, having the highest initial N content, decomposed compeletely in the shortest period (9 months). Root system studies suggest that A. hetrophyllus, Emblica and Paraserianthes are perhaps unsuitable for intensive mixing and close planting in agroforestry as they possess shallow and highly spreading root system. Ailanthus is perhaps a better candidate species for the above purpose as it possess relatively lower lateral root spread and at the same time having a deep tap root system. Root activity paatern of Artocarpus hisrsutus revealed that more than 75% of fine roots responsible for water nutrient absorption is concentrated in the 75 cm radius around the base of the tree. Recovery of 32P declined as depth of application increased. The combination of lowest lateral distance (75 cm) and depth (30 cm) accounted for more than 30% root activity.