Can productivity and post-pruning growth of Jatropha curcas in silvopastoral systems be regulated by manipulating tree spacing/arrangement without changing tree density?

Abstract

The potential of tree spacing/arrangement to alleviate effects of interspecific competition of hedgerow intercropping systems on productivity and response to pruning of Jatropha curcas was investigated using a Jatropha curcas -Pennisetum clandestinum (kikuyu) silvopastoral system at Ukulinga (KwaZulu Natal, South Africa). Treatments were differentiated by presence/absence of kikuyu and arrangement/spacing of Jatropha trees (one, two and three tree hedgerows on either side of the alley) and had the same tree density (1110 ha -1 ).When high water availability and kikuyu dormancy coincided, tree growth rates did not significantly differ across treatments. Trees of the treatment without interspecific competition (tree-only) were the tallest. Even when rainfall was high, post-pruning tree height growth rate was affected by belowground (BG) interspecific competition and tree spacing/arrangement. Treatment with a single tree hedgerow between alleys had the most frequent maximum stem growth rate and was the most efficient during limited water availability. Its trees showed slow initial response to pruning due to a high tree-grass interface, followed by compensatory growth when competition for water with grass was low. Generally, length of tree-grass interfaces affected yield inversely especially as trees matured toward their maximum-yield age (4-5 years). BG competition reduced tree

Optimizing resource distribution and crop productivity in hedgerow intercropping by manipulating tree arrangement

“…Jatropha and kikuyu are mostly dormant during extended dry periods and active during the rest of the year leaving no room for temporal complementarity between them. Ghezehei et al (2015) reported significant stem growth in the treatments of the current study, which was in agreement with a study by Huth et al (2010) that tree roots can explore intercropping zone for water before and during growing seasons. Taking into consideration total productivity (trees and grass) and total ET (Table 1), DR in our study was better tree arrangement than SR.…”

“…In the current study, tree arrangement without changing density had no consistent effects on tree growth and yield (Ghezehei et al 2015), and tree allometric relationships were not affected by interspecific competition or tree arrangements (Ghezehei et al 2009). High grass growth coincided with high rainfall periods, and grass yield consistently increased with increasing distance from tree rows, which was in agreement with previous studies (González-Hernández and Rozados-Lorenzo 2008; Huth et al 2010).…”

“…Unlike in previous studies, which showed reduced soil water content close to trees (Malik and Sharma 1990;Onyewotu et al 1995;Livesley et al 2000;Odhiambo et al 2001), our treatments did not exhibit consistent soil water increase or decreases towards tree hedgerows. Due to the absence of interspecific competition, JO had the biggest trees (Ghezehei et al 2015) and their roots did not have to explore the soil profile for water. SR and DR trees had comparable RGRs, yet DR had lower grass yield and its trees explored soil profile more comprehensively, which could suggest more intensive interspecific and intraspecific competition.…”

Is there life after hype for Jatropha? Exploring growth and yield in Indonesia

“…Research by Ghezehei et al (2015) showed yearly variations of HI from 0.5 % to 2.5 % in three year old jatropha-kikuyu grass silvopastoral, observed over a two year period. Our results are within these parameters.…”

“…Information on biomass partitioning in the reproductive part as fruit/seed yield or HI is limited, with exception of Ghezehei et al (2015), direct (economic) yield is the most common measure used. The reason for this is likely due to the fact that jatropha is a perennial and yield may not be harvested until several years after planting, which unlike HI for annuals is easily determined on seasonal or annual basis.…”