Performance of selected medicinal herbs under rubber and cashew plantations

Abstract

A field experiment was conducted at Vellanikkara, Thrissur, Kerala to assess the understorey productivity of three herbaceous medicinal crops viz. Zingiber officinale (ginger), Curcuma longa L. (turmeric) and Kaempferia galanga L. (Lesser galangal) under mature rubber (Hevea brasiliensis Muell. Arg,) and cashew (Anacardium occidentale L.) plantations. The biophysical attributes influencing the productivity of the land management systems and the biochemical changes in the products of understorey crops were studied. Additionally, soil carbon sequestration in both the given land use systems and the treeless open plot was estimated. Mean mid day (12–1p.m) understorey photosynthetic photon flux density (PPFD) levels were more in cashew (1275 μ moles m-2sec-1) than rubber (1072.5 moles μ m-2sec-1) with respective understorey PAR transmittance of 56.62percent and 44.1percent of full sunlight. The stand leaf area index (LAI) values in rubber and cashew were 1.98 and 1.43 respectively. Growth parameters of understorey crops varied noticeably among land use systems. Plant height and pseudostem length of ginger were greater in rubber and that of turmeric was in cashew. Leaf spread of galangal was higher in rubber. Root length of all crops was maximum in treeless open plot followed by cashew and rubber plantations. Ginger and turmeric exhibited highest tiller and leaf production in treeless open plot followed by cashew and rubber. However, higher tiller and leaf production in galangal were in rubber. Rhizome yield varied appreciably among the land use systems over the growth period. Rhizome yield at final harvest for ginger and galangal was maximum in treeless open (3.46 and 3.06 Mg ha-1 respectively) while that of turmeric was in the cashew plot (7.63 Mg ha-1) explicating the influence of PAR on understorey productivity. Regression equation relating PAR rhizome yields showed statistical reliability with high coefficient of determination (R2) values. Total chlorophyll content of understorey crops was highest in rubber followed by cashew and open. Oleoresin also showed such a trend with highest 148 percent of 10.68, 4.49 and 2.60 for turmeric, ginger and galangal respectively under rubber. However, nutrient accumulation in the above and below ground parts of all the crops was higher in cashew compared to rubber. With respect to carbon sequestration, soil organic carbon stocks in the upper most layer (0-20 cm) were higher in rubber (18.38 Mg ha-1) followed by cashew (18.28 Mg ha-1) and treeless open plot (15.07 Mg ha-1) validating the influence of trees in improving the soil through addition of organic matter. This zone being important from intercropping point of view, relevance of wooded land use systems for understorey productivity is emphasised. The total carbon stocks in 1m soil depth, were highest in cashew (68.70 Mg ha-1) followed by rubber (64.74 Mg ha-1) and open (52.04 Mg ha-1). It may be thus deduced from the present study that in terms of yield attributes, ginger, turmeric and galangal have better prospects in wooded land use system in general and the specific advantage of cashew over rubber was also obvious. This may be attributed to relatively better PAR transmission, higher nutrient accumulation and lesser root competition in cashew. Further, the better quality of rhizomes under comparably higher shade levels suggests their suitability in tree-based land use systems