Long-Term Effects of Organic Amendments on Soil Organic Matter Quantity and Quality in Conventional Cropping Systems in Switzerland

Ayumi Koishi,Thomas Guillaume,Alexandra Maltas,Sokrat Sinaj,Luca Bragazza

doi:10.3390/agronomy10121977

Abstract

Increasing soil organic carbon (SOC) in agroecosystems is a promising solution to simultaneously address climate change mitigation, adaptation, and food security. Yet, the best management practices that could achieve these goals remain to be identified. Here, we analyze the long-term effects of application of green manure, cereal straw, farmyard manure, and cattle slurry on SOC in a 37 year long field experiment in Switzerland. The treatment effects were compared against control conditions that received only optimal mineral fertilization. More specifically, this study aimed at evaluating the effect of organic amendments on SOC accumulation and distribution in different soil particle-size fractions by means of a set of indicators about organic matter quality (biological reactivity, humification index) and microbial activity (extracellular enzyme activities). In the absence of organic matter input, application of mineral fertilizers alone resulted in the lowest SOC content and the highest humification index of the bulk soil organic matter. Among the organic amendments, cereal straw, farmyard manure, and cattle slurry promoted a higher SOC content and a lower humification index due to an increase of SOC in the clay-size fraction. The annual C accrual reached 4.4‰ per year over 37 years with farmyard manure. The higher biological reactivity measured for the green manure and cereal straw amendments was associated with higher soil enzymatic activities, while C retention coefficients decreased by at least 2.5 times compared to animal-derived amendments. The low availability of nutrients in green manure and straw amendments as suggested by the high phosphatase and N-acetylglucosaminidase activities may indicate a reduction in C retention of organic matter inputs due to nutrient microbial mining with plant-derived amendments.

Highlights

Agroecosystems represent a great potential to sequester atmospheric carbon (C) in soils because of their strong soil organic carbon (SOC) depletion due to historical human land use [1,2]
We aimed to investigate the long-term dynamics of SOC in an agricultural soil receiving different types of organic amendments with contrasting stoichiometry and composition, i.e., mustard (Brassica juncea L.) green manure, wheat cereal straw, farmyard manure, cattle slurry, or mineral fertilizers alone at typical rates applied in the field
NotPspecified, discussed both nutrients being low in cereal straw as compared to farmyard manure and cattle slurry differences were deemed significant at a p-value < 0.05

Summary

Introduction

Agroecosystems represent a great potential to sequester atmospheric carbon (C) in soils because of their strong soil organic carbon (SOC) depletion due to historical human land use [1,2]. Despite the recent political awareness for increasing SOC in agroecosystems [4], severe losses of SOC are still reported in most conventional cropping systems due to intensive agricultural practices [5,6], in stockless farms due to an insufficient input of organic C [7]. Accurate quantifications of their long-term effect on SOC quantity and quality are sparse [13,14]. Recent studies emphasized the role of physical protection and mineral association of SOC as a crucial mechanism for long-term stability of SOC [15,16,17,18]. SOC can be found in heterogeneous states, i.e., free or bound to soil minerals, resulting in SOC fractions with different turnover rates [19,20,21]

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Discussion

Conclusion