A. M. Hammermeister

Nitrogen Management in Organic Potato Production

There is increasing interest in organic potato production in Canada, within a context of continuing strong growth rates for organic products globally. Using data from on-farm and station based trials, key characteristics of organic potato production in the Atlantic Canada region, notably the use of extended rotations involving leguminous crop green manures combined with organic amendments, low intensity of nitrogen and residual soil mineral N (RSMN) post harvest, and enhanced soil quality and health, are shown as sustainable outcomes of these systems. Data presented confirm nitrogen as the primary factor limiting total and marketable yields. Without additional N supplementation but following legume green manures (GMr) of red clover, or hairy vetch, potato yields and N uptake are shown to range from 30 to 35 Mg ha−1 and 100–125 kg N ha−1, respectively, while RSMN remains low. Combining N supplementation (with composts or dehydrated manures) with GMr consistently increased total and marketable yield. The effect of N supply and GMr type on pest (wireworm, Colorado potato beetle) population dynamics is also examined. Finally, synchronizing N supply in these systems with crop demand remains challenging and the potential to use novel soil tests and plant bioassays to improve N management in organic production systems is also discussed.

Agronomic benefits of alfalfa mulch applied to organically managed spring wheat.

Field experiments were established at two locations in Manitoba in 2002 and 2003 to determine N contribution, moisture conservation, and weed suppression by alfalfa mulch applied to spring wheat (Triticum aestivum L). Mulch treatments included mulch rate (amount harvested from an area 0.5×, 1× and 2× the wheat plot area), and mulch application timing (at wheat emergence or at three-leaf stage). Positive relationships were observed between mulch rate and wheat N uptake, grain yield, and grain protein concentration. At Winnipeg, the 2× mulch rates (3.9 to 5.2 t ha-1) produced grain yields equivalent to where 20 and 60 kg ha-1 of ammonium nitrate-N was applied in 2002 and 2003, respectively. Where mulch and ammonium nitrate produced equivalent grain yield, grain protein in mulch treatments was often higher than where chemical fertilizer was used. N uptake was also observed in the following oat (Avena sativa L.) crop. The highest mulch rate (2×) produced higher N uptake and grain yield of second-year oat comp...

Nitrogen Availability in an Organic Potato Crop Following 3-Year Transition under Contrasting Farming Systems

Organic farming systems often involve livestock and/or forages. However, managing soil nitrogen (N) availability by adjusting soil amendment rates and forage duration in crop rotations is a challenge. A 4-year experiment was conducted to evaluate N availability in the fourth year of organic potato systems with contrasting livestock and forage components. The experiment included three forage levels (0, 1, or 2 years of forage) through 4-year rotations starting with wheat (Triticum aestivum L.) and ending in potato (Solanum tuberosum L.). Within each forage level, three soil amendments (alfalfa meal, composted beef manure, and composted poultry manure) represented nutrient sources from stockless, ruminant, and monogastric systems, respectively. As farmers do, we modified the amendment application rate and timing by taking a system approach to reflect crop rotations. Nitrogen availability was higher in alfalfa meal compared with the composts varied with feedstocks. Nitrogen supply from soil amendments differed in the year of application, with no apparent N carryover effects. With increased forage frequency, soil N supply rates increased in the organic potato season following the 3-year transition period. The pre-experimental pasture with high soil fertility limited differences in plant N uptake among treatments. Nitrogen availability as indicated by potato N uptake was linearly related to cumulative amendment inputs in spite of different amounts of amendment input to different treatments.

Spring wheat yield response to variable seeding rates in organic farming systems at different fertility regimes

Seeding rates in organic systems should balance a crop’s competitive ability while maintaining grain yield and quality. A 2-yr study assessed the response of spring wheat (Triticum aestivum L.) to variable seeding rates (1 × conventionally recommended rate, 1.25 ×, 1.5 × and 2 × ) in a plot experiment in Nova Scotia and on organic farms across Canada. The plot experiment was a two-factor factorial assessing seeding rate and fertility. For the Canada-wide experiment, the four seeding rates were completely randomized on each farm. Wheat yield was highest at the 2 × seeding rate in 2003, but average crop emergence across all treatment combinations was only 56%. In 2004, crop emergence was 76% and the 1.25 ×, 1.5 × and 2 × seeding rates had greater yield than the 1 × rate. Seeding rate affected plant density and heads per square metre, but no differences were observed among rates for kernels per head or thousand kernel weight. Grain protein content was similar among seeding rates and was increased by the high...

Nutrient supply from organic amendments applied to unvegetated soil, lettuce and orchardgrass

Organic sources of nutrients are increasingly being used in horticultural and certified organic production. The nutrient-supplying potentials of poultry manure compost (PM), feather meal (FM), alfalfa meal (AA) and vermicastings (VC) and an unamended control were measured in a growth room experiment. The amendments were applied at rates equivalent to 200, 400 and 800 kg total N ha-1 to a soil of low fertility. Nitrogen supply rates and concentrations were measured over 6 mo in unvegetated pots using PRS™ probes and KCl extraction, respectively. Biomass of lettuce (Lactuca sativa L.) and orchardgrass (Dactylis glomerata L.) and N uptake of orchardgrass were measured. Repeated measures analysis revealed significant amendment × rate × time interaction effects for N supply rate and concentration. Of total N applied, available N was 50 to 70% in the FM and PM treatments, 10 to 40% in the AA treatments, and 10% in the VC treatments. High rates of FM and PM were toxic to lettuce but produced good orchard grass y...

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.

Grape Yield and Quality Response to Cover Crops and Amendments in a Vineyard in Nova Scotia, Canada

The increasing cost of synthetic fertilizers, combined with their associated environmental impacts and yield instability, has promoted the use of local waste products and cover crops in vineyards. We assessed the effects of cover crop mixtures combined with organic and industrial wastes on grape yield and quality over two full growing seasons in a vineyard (Vitis vinifera) in Eastern Canada. The experimental treatments were arranged in a nested design with three replicates. Four cover crop mixtures: (i) oats + pea + hairy vetch (OPV), (ii) oats mixed with red clover (ORCl), (iii) timothy + alsike + red clover (TM), and (iv) control with no cover crop (CONT) were applied to main plots and five fertility treatments (fertilizer without N [NDEF], full synthetic fertilizer [FERT], wood ash [WA], municipal solid food waste [MSFW], and mussel sediment [MS]) were applied to subplots. During the second growing season, only half of the subplots received fertility treatments. Grape yield for the most productive cover crop and amendment combinations were ORCl × MS (9.52 mg/ha) > OPV × MSFW (9.49 mg/ha) > TM × WA (8.81 mg/ha) > ORCl × MSFW (8.28 mg/ha). The lowest grape yields were obtained with combinations of CONT with either NDEF (3.86 mg/ha) or WA (3.61 mg/ha). The highest berry sugar concentrations among the cover crops were obtained under TM floor management combined with NDEF (16.43 Brix), MS (16.03 Brix), and MSFW (15.98 Brix). Grape yield was affected by cover crop only during the second growing season, but berry sugar was not. Cover crop floor management strategies and organic or industrial wastes can be used as sources of nutrients or soil conditioners for vineyards in the cool humid climate of Eastern Canada.