Effect of prunning on light distribution and prediction of canopy photosynthesis rates upon two mango cultivars

Study on light distribution and prediction of canopy photosynthesis rates upon two mango cultivars, 'Nam Dok Mai' (NDM) and 'Kiew Sawoey' (KSW), was established. There were 4 pruning types used : (1) no pruning (control), (2) pruning and left 2 outermost flush shoots, (3) pruning and left 1 outermost flush shoots, and (4) 90 percent pruned out. The results showed that canopy light interception of these two mango cultivars were almost in equally value of both before and after pruning. Measuring of 92-95 percent interception was observed just before pruning and the control trees of type (1). This figure was quite stable throughout the experiment. Immediately after pruning, decreasing in light interception of 9, 18 and 52 percent were measured from the type (2), (3) and (4) respectively. Newly flush shoots and its growth provided an increasing light interception percentage, 91, 93 and 81 percent for type (2), (3) and (4) respectively, at the end of experiment. A close relationship was found between light interception or penetration and leaf area index (LAI or drip line LAI; DLLAI). Low LAI value (excessive pruning) was associated with low percentage of interception and showed the same pattern of heightening value. There was no further increasing in light interception (saturation) when the LAI increased to some certain point. DLLAI before pruning of both mango cultivars were ranged between 5.9-6.1. However, these values of pruning type (2), (3) and (4) were measured 2.8, 2.4 and 1.1 just after pruning and 3.4, 4.2 and 2.4 at the termination time, respectively. The average light extinction coefficient (k), from calculation, were 0.5 for 'NDM' and 0.6 for 'KSW'. The predicted values of daily canopy photosynthesis rates (Pd) were almost equally in value of both cultivars. The maximum Pd of 'KSW' was found to be higher than the 'NDM'. Maximum Pd of 'NDM' was 0.23 mol/square m/d at DLLAI 3.1-3.4 and k = 0.45 while 'KSW' obtained 0.29 mol/square m/d at DLLAI 2.2-2.7 and k = 0.60.