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

Michael Asigbaase,Evans Dawoe,Barry H. Lomax,Sofie Sjogersten

doi:10.1007/s11368-020-02844-4

Abstract

PurposeAlthough 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 methodsDynamics 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.ResultsThe 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.ConclusionsOrganic 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.

Highlights

Purpose 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 dependent on nutrient returns from decomposing litter
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 estimated k values for both litter decomposition and nutrient mineralisation correlated with soil pH and moisture content, but not initial litter chemistry

Summary

Introduction

Cocoa production is worth over 12 billion US$ and provides livelihoods for 40–50 million people worldwide (Hütz-Adams et al 2016). There is a growing demand for cocoa, its production is at cross-roads due to depletion of soil nutrients (ICCO 2014; Hütz-Adams et al 2016; Kaba 2017). Depletion of soil nutrients and organic matter is a serious threat to sustaining cocoa production in West Africa and elsewhere (Daymond et al 2017; Kaba 2017). Dwindling soil nutrients limit cocoa production in major cocoa-producing countries (Hütz-Adams et al 2016; Daymond et al 2017; Kaba 2017).

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Results

Conclusion