INFLUENCE OF TREE - CROP DISTANCE ON GROWTH OF Pinus patula AND Cupressus lusitanica YOUNG PLANTATIONS IN A PELIS SYSTEM

Abstract

The success of plantation tree species’ growth from planting to canopy closure depends on optimal tree-crop distance. Several studies have examined tree-crop distance in explaining the growth of plantation tree species. However, there are few published studies on the influence of tree-crop distance on establishment and growth of plantation tree species in a PELIS system. Therefore, this study was done to determine the influence of tree-crop seedling distance, tree species (Pinus patula and Cupressus lusitanica) age at planting, single (potatoes) and mixed cropping (cabbages and potatoes) and soil characteristics (bulk density and nutrients) on growth of Pinus patula and C. lusitanica seedlings in a PELIS system. The study was done to determined: i) the effect of tree-crop distance on growth of P. patula and C. lusitanica; ii) the influence of seedlings species age in the tree nursery and tree-crop distance on growth of P. patula and C. lusitanica species; iii) the effect of single (potatoes) and mixed (potatoes and cabbages) cropping and tree-crop distance on growth of P. patula and C. lusitanica tree species iv) the effect of soil characteristics (Bulk density, pH, Carbon, Nitrogen and phosphorus) and tree-crop distance on growth of P. patula and C. lusitanica tree seedlings species. Two sites (Timboroa and Kipkurere forests) practicing PELIS were used for the study. The normal seedling spacing for C. lusitanica is 250cm × 250cm and for P. patula is 275cm × 275cm. The study was about tree-crop interactions and hypothetical distances crops can be from the trees. Four treatment plots of tree distance (variable) were used in three replicates. The treatments were 20 cm, 50 cm, 100 cm and 150 cm. The control for the experiment was at tree-crop distance of 20 cm. Samples of 9 planted tree seedlings (3 × 3) were sampled for growth measurements. Root collar diameter (RCD) and height growth were measured monthly for P. patula and C. lusitanica from time of planting for 6 months. In each sample, soil samples were collected to determine; - Bulk density, soil pH, Carbon, Nitrogen and phosphorus. Mean values of RCD and height in all treatments were tested with ANOVA and significant different means were discriminated using Turkey’s HSD test. The relationship between growth trends in height and RCD against time were displayed using response surface methodology. Although the data optimize tree-crop distance was found to be 100cm, farmers are unlikely to accept such a wide distance. Therefore, to improve the current situation, this study recommends a practical distance of either 25 or 50cm in height and RCD for P. patula and C. lusitanica in Timboroa and Kipkurere forests. Growth in height and RCD were lowest at tree-crop distance 150cm. Planting of P. patula and C. lusitanica at age 12 months resulted to better growth at tree-crop distance of 100 cm followed by 50 cm than the control (20 cm) in Timboroa and Kipkurere forests. The final height and RCD of P. patula and C. lusitanica was higher in treatment with mixed cropping compared to single cropping, with significant interactions between the tree-crop distance and single and mixed crops affecting growth. The management implications of this study are that crop-tree distances in a PELIS system should be 100 cm and not closer. In addition, older seedlings may perform better than very young ones. Site nutrients are not impacted by crop-tree distance but there is confounding with single and mixed cropping and fertilizers normally added by farmers in a PELIS system. More studies are needed on nutrients and single and mixed cropping interactions, especially if robust crops casting a lot of shade like maize are used.