Effect of cutting height on non-structural carbohydrates, biomass production and mortality rate of pigeon peas

Inadequate nutrition limits small-scale livestock production by smallholder farmers in South Africa but can be addressed by the introduction of woody fodder species. Cutting woody plants to harvest fodder affects their productivity and thus it is necessary to determine the optimum cutting height. Cutting affects the productivity and survival of woody plants because it alters concentrations of non-structural carbohydrates, which are used to support their recovery. Since pigeon pea (Cajanus cajan (L.) Millsp.) is not widely grown in South Africa and is not managed as a pruned hedgerow, there was a need to investigate the effect of cutting height under local conditions, especially in areas that experience frost. The trial was established in November 2016, ran over two growing seasons (2016/2017 and 2017/2018) and concluded in August 2018. The treatments comprised three silvopastoral systems with Panicum maximum planted between pigeon pea hedgerows that were cut at 60 cm and 90 cm above the ground, or left uncut and sole P. maximum. Over the two year period, the pigeon pea plants cut at 90 cm above ground produced significantly more leaf, twig and total biomass than the plants cut at 60 cm. Cutting height also had a significant effect on the percentage twig, with pigeon pea plants cut at 90 cm having significantly higher percentage twig than those cut at 60 cm (P   0.05). In July 2018 there were a number of days with temperatures below 0 °C. Prior to this no mortalities had been observed, but the frost events resulted in die-off. The mortality rates were determined in August 2018 when it was clear which of the shrubs had clearly died. The shrub mortality rates were higher for pruned relative to unpruned shrubs, but the effect was not significant (P > 0.05). It was concluded that the choice of cutting height is important for maximising browse production. Future research should consider the effect of pruning on non-structural carbohydrate concentration and total pool in the roots to better understand the reasons for reduced production and shrub mortalities.