Ion exchange membranes as an indicator of soil mineral nitrogen availability and nitrogen uptake by arugula (Eruca sativa L.) in soils amended with green manure

Abstract

Green manure crops are a common N fertilizer source in organic agriculture. Producers need guidance on when to incorporate the green manure for efficient N uptake by the following crop. The objective of this study was to describe the temporal dynamics of soil mineral N following green manure plough-down and N available to arugula (Eruca sativa L. sp.) also known as salad rocket, a fast-growing leafy herb used in salads. Green manure was a mixture of field pea (Pisum sativum L.) cv. CDC Meadow and oat (Avena sativa L. sp.) grown on fields with sandy loam and sandy clay loam soils at an organic vegetable farm in southwestern Quebec, Canada. Ion exchange membranes (IEMs) were used to monitor the ammonium (IEM––N) and nitrate (IEM––N) released following green manure plough-down. The IEM––N concentration was positively correlated with rainfall (r = 0.57 to 0.95, p < 0.05) and was greater from 2 to 5 weeks after green manure plough-down than in soils without green manure. Arugula N uptake and IEM––N were positively correlated in sandy clay loam (r = 0.86, p < 0.01) and sandy loam (r = 0.71, p < 0.05) soils. IEM––N concentrations were found to be sensitive to weather, green manure decomposition and arugula growth, and could be a tool to monitor soil mineral N available for short-season vegetable crops.

Keywords:

• Eruca sativa L
• green manure
• ion exchange membrane
• nitrogen mineralisation
• soil nitrogen availability

Acknowledgements

We appreciate the insights and helpful comments from two anonymous reviewers and Editor on earlier drafts of this paper. We thank the cooperating producer and Natural Sciences and Engineering Research Council of Canada (NSERC) for support through grant numbers 2383823-10 and EGP 448886-13. LLC was supported by a scholarship from SENESCYT (Ecuador).