The effect of green manure and organic amendments on potato yield, nitrogen uptake and soil mineral nitrogen

Abstract

Fertility management is challenging for organic crops with intensive nutrient demands such as potatoes (Solanum tuberosum L.). Four crop sequences varying in pre-potato green manures as main plots and four fertility treatments applied in the potato phase only [control, inorganic fertilizer (FERT), municipal solid food waste compost (MSW) and paper mill biosolid compost (PMB)] as subplots were compared in five-year organic potato rotations in Eastern Canada. Potato yields did not differ significantly between crop rotations; however, soil amendments had significant impacts on potato yields. Averaged across years, total tuber yields were in the order; FERT (34.2 Mg ha⁻¹) > MSW (29.6 Mg ha⁻¹) > control (26.5 Mg ha⁻¹). Total potato N uptake (TNU) levels were 89, 115, 107 and 147 kg N ha⁻¹, respectively, for control, MSW, PMB and FERT, and were greater when potato followed red clover (119–124 kg N ha⁻¹) compared with oat/pea/vetch mixture (107–108 kg N ha⁻¹). Plant N use efficiency (NUE) was 299, 263, 263 and 235, respectively, for control, MSW, PMB and FERT. Pre-plant soil mineral N (SMN) ranged between 39 and 112 kg N ha⁻¹ among different crop rotations. During the tuber initiation stage, SMN ranged between 40 and 66 kg N ha⁻¹ while during tuber bulking it ranged between 10 and 14 kg N ha⁻¹ among different crop rotations and soil amendments. Post-harvest SMN ranged between 8 and 30 kg N ha⁻¹ for all rotations and amendment treatments.

Keywords:

• Legume green manure
• mineral nitrogen
• municipal solid food waste
• organic potato
• paper mill biosolid

Acknowledgements

The authors wish to acknowledge support for the principal author provided by the Canada Research Chairs Program. The keen interest and assistance of many organic producers and research technicians, too numerous to list, is also greatly acknowledged.