Decomposition and nutrient mineralisation of leaf litter in smallholder cocoa agroforests: a comparison of organic and conventional farms in Ghana

Abstract

Purpose Although litter decomposition and nutrient release patterns have been studied in cocoa agroforestry systems in general, studies focusing on organic and conventional cocoa systems are lacking which is critical as organic farms are particularly dependent on nutrient returns from decomposing litter. Materials and methods Dynamics in leaf litter decomposition and the mineralisation of macro- and micro-nutrients in organic and conventional cocoa agroforestry systems were studied using the litterbag technique for 12 months. Results The average monthly mass loss was more than two times higher on organic farms (9.2–14.4 g month−1) compared to conventional farms (4.2–7.3 g month−1) in the first five months. The annual rate of decomposition (k) was higher on organic farms (1.9) compared to conventional systems (1.4). The time required for 50% (t50) and 99% (t99) decomposition of leaf litter was both lower on organic farms (t50 = 0.4 years, t99 = 2.6 years) than conventional farms (t50 = 0.5 years, t99 = 3.5 years). The estimated k values for macro- and micro-nutrients on organic cocoa systems ranged from 2.3 for calcium to 4.5 for potassium compared to 1.6 (Ca) to 2.8 (K) on conventional farms. The k values of all nutrients (except nitrogen and phosphorus) were significantly greater on organic farms than conventional systems. The estimated k values for both litter decomposition and nutrient mineralisation correlated with soil pH and moisture content, but not initial litter chemistry. Conclusions Organic management of smallholder cocoa agroforestry systems enhanced leaf litter decomposition and nutrient mineralisation through improved soil conditions. Thus, organic management of cocoa agroforestry systems may contribute to sustainable cocoa production in smallholder systems through enhanced nutrient return from litter decomposition.

Decomposition Rate of Organic Residues and Soil Organisms’ Abundance in a Subtropical Pyrus pyrifolia Field

“…On the other hand, the observed results show strong evidence about the soil organisms' activity on mulching decomposition on plots where compost was applied using litterbag with 15 mm 2 mesh-type. These results agree with the previous studies that reported positive effects of organic residues management on soil organic matter dynamics [17,43,44]. These studies have reported soil improvements, and soil organisms' activity with the continuous use of compost and green manure practice in tropical and subtropical soils.…”

Temporal changes in litterfall and potential nutrient return in cocoa agroforestry systems under organic and conventional management, Ghana

“…However, in agroforestry systems such as cocoa agroforestry, the management approach affects litter decomposition, which in turn, enhances or reduces nutrient supply rate through nutrient cycling (Becker et al, 2015;Fontes et al, 2014;Ofori-Frimpong et al, 2007). For example, non-synthetic agrochemical use was enough to enhance litter decomposition and nutrient mineralization in organic systems compared to conventional systems due to the presence of more well adapted decomposer communities in organic systems (Domínguez et al, 2014;Asigbaase et al, 2021a).…”

Balancing litterfall and decomposition in cacao agroforestry systems

“…However, in the tropics, the role of litter chemistry still dominates. Litter decomposition rates in smallholder cacao agroforests in Ghana correlated with soil moisture content and pH, but not litter chemistry (Asigbaase et al 2020). In contrast, litter quality was a predominant driver of decomposition rates along a land-use gradient, including cacao agroforestry at plot/farm scale (Dawoe et al 2009;Fanin et al 2016;Hoeber et al 2020;Tanner 1981).…”

“…Reciprocal litter exchange experiments tested the combined effect of litter quality and environmental conditions on the rate of litter dry weight loss in relation to soil conditions (biota, nutrient supply, temperature, soil moisture) in forests, agricultural fields and grasslands (Asigbaase et al 2020;Hättenschwiler and Jørgensen 2010;Hoeber et al 2020;Liu et al 2010;Rachmawati et al 2019;Schilling et al 2016;Wang et al 2015). Beyond effects of litter quality and microclimate, the interaction between substrate quality and composition of the microbial community also influences litter decomposition (Fanin et al 2016;Fierer et al 2005).…”