Excessive Nitrate Limits the Sustainability of Deep Compost Mulch in Organic Market Gardening

Abstract

Market gardening is a widespread practice of bio-intensive vegetable production characterized by direct marketing, small-scale farming structures, high crop densities, and innovative cultivation approaches. Currently, deep compost mulch (DCM) is a popular trend among related growing techniques. The combination of no-till and a permanent mulch of compost aims to improve soil fertility, regulate soil temperature, retain soil moisture, and control weeds. To address the problem of perennial weeds in organic no-till, deep mulch layers of typically 150 mm are used. The amount of compost required and the associated N inputs are immense and carry the risk of environmentally harmful N surpluses that can be lost through nitrate leaching or denitrification. The aim of this study is to evaluate the use of compost as mulch and to investigate N dynamics under DCM. For this purpose, a literature review was conducted, and soil inorganic nitrogen (Nmin-N) was measured under on-farm conditions up to a soil depth of 900 mm in a market garden with DCM in Germany for one year. Furthermore, based on the collected data, the different N pathways were calculated using the N-Expert and NDICEA models and simulated for two additional scenarios. Results from field measurements showed a strongly increased N-surplus not taken up by the crops and a shift of Nmin-N to deeper soil layers for municipal organic waste compost (MW), with an average accumulation of 466 kg Nmin-N ha−1 at 600–900 mm depth. N inputs from DCM can be significantly reduced by the use of green waste compost (GW) with low bulk density or wood waste compost (WW) with an additional high C/N ratio.

Securing agropastoral system and rural livelihood through the market garden in Niger: unfolding smallholders’ resilience to interwoven challenges

“…In the study areas, farmers utilized inputs consisting of seeds, fertilizers, and plant protection products. Market gardeners understand the dynamic nature of soil fertility, recognizing the necessity of cultivating multiple crops that sustain and enhance their productive capacity (Ruch et al, 2023).…”