Tree species and pruning regime affect crop yield on bench terraces in SW Uganda

Abstract

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Trees improve water storage and reduce soil evaporation in agroforestry systems on bench terraces in SW Uganda

“…4g), suggesting that greater lateral extension of its roots 490 into the cropping area compared to the other tree species examined created a more extensive 491 spatial hydrological influence. Siriri et al (2010) noted that calliandra depressed crop yield 492 for distances of up to several metres from the tree line, supporting evidence that the roots of 493 this species are highly versatile and may extend over considerable lateral and verticalresponsible for the significant reduction in  w relative to the sole crop control treatment, supporting the supposition that, although E s was reduced (Fig. 2b), the water saved wasabsorbed by its extensive root system.…”

“…The lack of any crop yield response to 515 root+shoot pruning sesbania during five cropping seasons when beans or maize were grown 516 substantiates the absence of any adverse effect unpruned trees on  w in the adjacent cropping 517 area; indeed, the presence of unpruned sesbania on the upper terrace increased values for  w 518 in the cropping area, whereas unpruned calliandra trees competed strongly for water and 519 reduced  w on the lower terrace and the yield of bean and maize crops by c. 40% over six 520 cropping seasons during which rainfall varied greatly (Siriri et al, 2010). The pruning 521 intensity used here may have been insufficient to control competition effectively; thus, a 522 more extreme management regime than annual root pruning to 30 cm depth when the trees 523 were young and 50 cm when they reached three years of age may be required for calliandra.…”

“…The observation that root+shoot pruning alnus and the tree mixture increased  w on the lower 512 terrace, but had no detectable effect in the calliandra and sesbania treatments (Table 3) 513 reflects the finding that pruning the latter two species did not improve crop performance, 514 although for different reasons (Siriri et al, 2010). The lack of any crop yield response to 515 root+shoot pruning sesbania during five cropping seasons when beans or maize were grown 516 substantiates the absence of any adverse effect unpruned trees on  w in the adjacent cropping 517 area; indeed, the presence of unpruned sesbania on the upper terrace increased values for  w 518 in the cropping area, whereas unpruned calliandra trees competed strongly for water and 519 reduced  w on the lower terrace and the yield of bean and maize crops by c. 40% over six 520 cropping seasons during which rainfall varied greatly (Siriri et al, 2010).…”

“…in Uganda have shown that unpruned sesbania fallows on the upper terrace had little impact 124 on crop yield on the lower terrace, but that shoot and/or root pruning of alnus and, especially, 125 calliandra was needed to maintain crop yield (Siriri et al 2010). Trees were grown on the upper third of the terrace for four years, while cropping continued 158 on the middle and lower parts of the terrace (Fig.…”

“…The pruning 521 intensity used here may have been insufficient to control competition effectively; thus, a 522 more extreme management regime than annual root pruning to 30 cm depth when the trees 523 were young and 50 cm when they reached three years of age may be required for calliandra. 524 unpruned sesbania had little impact on crop yield on the lower terrace, whereas pruning of 529 alnus and, especially, calliandra was vital to maintain crop yield (Siriri et al 2010). The 530 present study has revealed that some tree species have beneficial effects on E s and  w in the 531 adjacent cropping area and that the effects of pruning on crop yield were associated with 532 reductions in E s and increases in  w .…”