Rhizosphere management for enhancing root productivity and oil yield in vetiver (Vetiveria zizanioides (L.) Nash.

Abstract

Vetiver is the only grass cultivated specifically for its root essential oil, a complex mixture of sesquiterpene alcohols and hydrocarbons, used extensively in perfumery and cosmetics. The World Bank has promoted the Vetiver System since the 1980s for various applications such as soil erosion and sediment control, water conservation, landslip and riverbank stabilization and recently for pollution control. However, cost effective techniques for increasing root production in the humid tropics are lacking. The present investigation was carried out at the College of Agriculture, Vellayani to study the effect of planting methods, subsurface drip fertigation and combined application of bioinoculants on root and oil yield in vetiver (Vetiveria zizanioides). The technical programme consisted of combinations of three planting methods, viz, P1 – Planting in coconut husk mulched trenches, P2 – Planting in coconut husk lined trenches and P3 – Planting on the ridges, two levels of fertigation, viz, F1 – Subsurface drip fertigation and F2 - No fertigation; and two bioinoculants, viz, B1 - Application of bioinoculants and B2 - No bioinoculants. The trial in Factorial RBD was conducted during 2010-11. Planting methods, fertigation levels and application of bioinoculants influenced various growth characters of vetiver, viz., plant height, number of leaves and tiller production at various stages of growth. In general, planting in coconut husk lined trenches resulted in better performance. Installation of sub surface drip fertigation system and application of bioinoculants also encouraged vegetative growth. The effect of the above treatments on number, length, spread, volume and weight of vetiver roots were found to be remarkable at certain stages of growth. In general, planting in coconut husk lined trenches was found to improve all the root parameters studied when compared to ridge planting. The effect of bioinoculant application was also conspicuous in improving root growth compared to control (no inoculation). Planting vetiver slips treated with bioinoculants in coconut husk lined trenches under sub surface drip fertigation 111 system provided a favourable situation for root elongation during the early phase of crop establishment. Planting methods, fertigation levels and application of bioinoculants had no significant effect on any of the physiological parameters, viz, canopy temperature, relative leaf water content and osmotic potential studied. Significant influence of planting methods on chlorophyll a and total chlorophyll were observed. Planting on ridges (P3) which was on par with planting in coconut husk lined trenches (P2) showed significantly higher contents of chlorophyll a and total chlorophyll. Leaf dry matter production at all stages and root dry matter at certain stages were found to be significantly influenced by the main effects of treatments. Similar to biometric characters, leaf and root dry matter production were found highest when vetiver was planted in coconut husk lined trenches. Sub surface drip fertigation had a positive and significant effect in enhancing leaf and root dry matter production. The effect of bioinoculants was also positive and significant in improving the above parameters when compared to control. Among the different planting methods, planting in coconut husk lined trenches registered the highest value of soil moisture content before irrigation which was closely followed by planting in coconut husk mulched trenches. The effect of sub surface drip fertigation in influencing soil moisture content before and after irrigation was remarkable. However, application of bioinoculants was not found to significantly influence soil moisture contents. Planting in coconut husk lined trenches (P2), installation of sub surface fertigation system and application of bioinoculants enhanced root and oil yield. Economic analysis of the system also proved the superiority of planting vetiver in coconut husk lined trenches (P2), installation of sub surface drip fertigation system and application of bioinoculants in improving gross and net income. APPEND