Forage biomass and soil aggregate carbon under fodder banks with contrasting management regimes

Abstract

Fodder banks are important agroforestry technologies that improve access to off-season livestock feed among smallholder farmers. However, fodder banks also contribute to nutrient mining, through biomass transfer, and therefore their sustainably may be downplayed. In order to identify sustainable managemt options, the objective of this study was to determine the effect of management practices (spacing and pruning frequency) on forage yield and soil organic carbon (SOC) of two contrasting leguminous Calliandra calothyrsus Meissner and non-leguminous (Vernonia amygdalina Del) fodder shrubs. A field trial, with the two shrubs separately planted at different spacing (0.75 × 0.75 m and 1.0 × 1.0 m) and frequency of complete pruning (5- and 9-week interval), was established in a three-replicate randomized complete block design. Harvesting of fodder biomass was done for two consecutive years from the start of pruning. Total and aggregate SOC of the top soil (0–15 cm) and sub-soil (0.15–0.30 m) was assessed in four particle-size fractions. For both species, wider spacing significantly reduced (p = 0.037) forage biomass by approximately 20%. Pruning at 9-weeks produced more forage biomass for C. calothyrsus, but not for V. amygdalina. The size of the soil aggregates significantly increased (p = 0.027) by 8% in the 9-week compared to 5-week pruning frequency. Total organic carbon (TOC) in sub soil under C. calothyrsuswas 7% higher than that under V. amygdalina. Wider spacing and lower pruning frequency significantly increased OC in sub soil (p = 0.003) by 4% and 9%, respectively. Therefore, a spacing of 1.0 m combined with a pruning frequency of 9 weeks is optimum for forage and SOC. These results suggest that the sustainability of fodder banks can be achieved by optimizing pruning frequency and plant spacing. Therefore, proper management of fodder banks can contribute to climate-smart agriculture through increasing soil carbon sequestration and increased livestock productivity among stallholder farmers.