Optimum Pruning Strategies for Reducing Crop Suppression in a gmelina-maize Smallholder Agroforestry System in Claveria, Philippines

On-farm trials were conducted to assess the effects of four branch pruning levels on maize grain yield, tree growth and stem shape. The experimental plots consisted of gmelina (Gmelina arborea R.Br.) trees planted at 1 x 10 m with maize intercropped in the 10 m-wide alleys between lines of trees. Pruning levels consisted of retaining a live crown ratio of 60-’70% (T1), 40-50% (T2); 30-40% (T3) and of 20-30% (T4). At the end of the experiment, the total maize grain yield was highest under the high pruning intensity (T4) (18.06 t ha-1) and lowest under T1 (14.48 t ha-1). Maize grain yield under the pruning regime T2 and T3 were 16.08 and 17.21 t ha-1 respectively. Mean annual increment (MAI) in tree diameter was greater (5.0 cm yr-1) under T1 than those at T4 (4.1 cm yr-1). Pruning regimes T2 and T3 resulted in a MAI of 4.7 cm yr-1 and 4.5 cm yr-1 respectively. Financial analysis showed that maize-tree systems under T4 were more profitable than under T1 as long as the reduction of the average dbh at harvest were not greater than 1 cm. Pruning trees intensively also generated greater returns from labour than moderate pruning, as the greater maize grain yields under T4 compen sated for the cost of pruning and the lower timber yield. In the context of resource-poor farmers, intensive branch pruning was a practice that prolonged the period of profitable intercropping and was compatible with commercial timber production.