Productivity, Soil Quality Changes and Nitrogen Losses Under Extended Organic Vegetable Rotations

Derek Lynch¹, Mehdi Sharifi², David Burton² and Andy Hammermeister³

Abstract
Organic cropping systems are often characterized by extended rotations (4yr+) involving leguminous green manures, with benefits to soil quality/soil health. Much less is known regarding nitrogen losses to air and water and overall nitrogen efficiency of these systems.

Since 2006, the impact of green manure type and frequency, with or without organic amendment or fertilizer, on soil quality, greenhouse gas emissions and overwinter N losses are being evaluated under four 5yr vegetable rotations at NSAC. Three pre-potato (Solanum tuberosum L.) sequences include: C1 (oats underseeded with red clover-red clover), C3 (carrots-oats/ pea/vetch mixture (OPV)) and C4 (beans followed by buckwheat-OPV). Soil fertility treatments include: nonamended potatoes (control), supplemented with P and N fertilizer (FERT), municipal food waste compost (MSW), or composted paper mill biosolids (PMB).

In 2008, higher soil mineral N (SMN) (125 vs. 85 kg N ha^-1) and mineralizable N were measured prior to potatoes in C1 compared with C3 and C4 with more than 80% of the seasonal decrease in SMN attributed to potato N uptake. Spring soil N supply rate measured in-situ by PRSTM ion exchange membranes was 58% greater in C1 compared with C3. Particulate organic C averaged 21% of total soil C but was unaffected by treatment. Amendment treatments but not rotations influenced microbial biomass and microbial quotient, with 50% higher values measured for MSW compared with FERT and PMB. About 30 kg N ha^-1 was SMN estimated lost from the root zone (0- 30 cm) over winter (2008-2009) and was unaffected by treatments. N₂O emissions under potatoes ranged from 1.30 to 0.28 kg N₂O-N ha^-1 for C1 and C3 sequences. In control subplots, emissions were 31% lower than under the FERT treatment (1.31 vs. 1.72 kg N₂O-N ha^-1) but double that obtained for a standing red clover crop. Additional data for 2009 will also be presented.

Source
Proceedings of the Joint Conference of the Canadian Society of Soil Science and the Canadian Society of Agronomy, Beyond Organics session. Saskatoon, Saskatchewan. 20-24 June 2010.

Author Locations and Affiliations
(1) Department of Plant and Animal Sciences, Nova Scotia Agricultural College
(2) Department of Environmental Sciences, Nova Scotia Agricultural College
(3) Organic Agriculture Centre of Canada, Department of Plant and Animal Sciences, Nova Scotia Agricultural College

Posted July 2010


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Research Extension Courses Consumers -------------------------- Virtual Tours Student & Job Opportunities News Articles Standards -------------------------- Market Information Events Issues Animal Welfare Strategic Plans -------------------------- Links Award-winners Site Map	Productivity, Soil Quality Changes and Nitrogen Losses Under Extended Organic Vegetable Rotations Derek Lynch¹, Mehdi Sharifi², David Burton² and Andy Hammermeister³ *Abstract* Organic cropping systems are often characterized by extended rotations (4yr+) involving leguminous green manures, with benefits to soil quality/soil health. Much less is known regarding nitrogen losses to air and water and overall nitrogen efficiency of these systems. Since 2006, the impact of green manure type and frequency, with or without organic amendment or fertilizer, on soil quality, greenhouse gas emissions and overwinter N losses are being evaluated under four 5yr vegetable rotations at NSAC. Three pre-potato (Solanum tuberosum L.) sequences include: C1 (oats underseeded with red clover-red clover), C3 (carrots-oats/ pea/vetch mixture (OPV)) and C4 (beans followed by buckwheat-OPV). Soil fertility treatments include: nonamended potatoes (control), supplemented with P and N fertilizer (FERT), municipal food waste compost (MSW), or composted paper mill biosolids (PMB). In 2008, higher soil mineral N (SMN) (125 vs. 85 kg N ha^-1) and mineralizable N were measured prior to potatoes in C1 compared with C3 and C4 with more than 80% of the seasonal decrease in SMN attributed to potato N uptake. Spring soil N supply rate measured in-situ by PRSTM ion exchange membranes was 58% greater in C1 compared with C3. Particulate organic C averaged 21% of total soil C but was unaffected by treatment. Amendment treatments but not rotations influenced microbial biomass and microbial quotient, with 50% higher values measured for MSW compared with FERT and PMB. About 30 kg N ha^-1 was SMN estimated lost from the root zone (0- 30 cm) over winter (2008-2009) and was unaffected by treatments. N₂O emissions under potatoes ranged from 1.30 to 0.28 kg N₂O-N ha^-1 for C1 and C3 sequences. In control subplots, emissions were 31% lower than under the FERT treatment (1.31 vs. 1.72 kg N₂O-N ha^-1) but double that obtained for a standing red clover crop. Additional data for 2009 will also be presented. Source Proceedings of the Joint Conference of the Canadian Society of Soil Science and the Canadian Society of Agronomy, Beyond Organics session. Saskatoon, Saskatchewan. 20-24 June 2010. Author Locations and Affiliations (1) Department of Plant and Animal Sciences, Nova Scotia Agricultural College (2) Department of Environmental Sciences, Nova Scotia Agricultural College (3) Organic Agriculture Centre of Canada, Department of Plant and Animal Sciences, Nova Scotia Agricultural College Posted July 2010
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Productivity, Soil Quality Changes and Nitrogen Losses Under Extended Organic Vegetable Rotations

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