Sean M. Westerveld

Nitrogen and water requirements of fertigated cabbage in Ontario

Increasing nutrient and water regulations have necessitated development of best management practices for application of nitrogen (N) and water. This study was conducted to determine if there was an optimal balance of N and water applied for late storage cabbage (Brassica oleracea L. var. capitata). Five rates of N and five irrigation rates arranged in a response surface design replicated three times were supplied to Huron cabbage grown on sandy loam soil to study the interaction of N and water applied. Plots were located at the University of Guelph, Simcoe Research Station, Ontario, Canada from 2003 to 2005. Total and marketable yields were maximized from a low of 278 kg ha-1 N in 2005 to above the highest rate tested (400 kg ha-1 N) in the other 2 yr. In 2005, there were 29 d above 30 °C and marketable yield was 49% lower than 2004, which had only 1 d above 30 °C. A target soil water value of 100% of field capacity was required to maximize yield in all 3 yr. More N is required as the water supply increas...

Effect of Foliar Trimming and Fungicides on Apothecial Number of Sclerotinia sclerotiorum, Leaf Blight Severity, Yield, and Canopy Microclimate in Carrot

Foliar trimming of the carrot canopy has potential for reducing the severity of Sclerotinia (Sclerotinia sclerotiorum) rot of carrot (Daucus carota subsp. sativus). The effect of trimming the carrot foliage once or twice, with and without fungicide application, was examined on carrot plants grown on organic soil for 3 years at the University of Guelph-Muck Crops Research Station in Ontario, Canada. The number of S. sclerotiorum apothecia, carrot leaf blight (CLB; Alternaria dauci and Cercospora carotae) severity, canopy microclimate, and total and marketable yield were assessed. The number of apothecia of S. sclerotiorum and relative humidity in the canopy were reduced by trimming done at either the first observation of apothecia or at 100 days after seeding (DAS). In both cases, the effects of trimming on canopy microclimate lasted between 2 and 4 weeks. Trimming the canopy twice during the season did not reduce the number of apothecia compared with trimming the canopy once at 100 DAS. Foliar trimming had little effect on CLB severity. This was attributed mainly to the lower requirement of the CLB pathogens for prolonged periods of high relative humidity and leaf wetness compared with S. sclerotiorum. Foliar trimming did not improve the efficacy of fungicide applications for CLB control. Trimming the canopy once or twice had no effect on total or marketable yield. Thus, trimming has potential to improve the management of Sclerotinia rot of carrot, and trimming both at first observation of apothecia and at 100 DAS could reduce apothecia production and relative humidity within the canopy.

Establishment of Critical Sap and Soil Nitrate Concentrations using a Cardy Nitrate Meter for Two Carrot Cultivars Grown on Organic and Mineral Soil

Abstract Nitrate (NO3 −) meters have been used effectively for crop nitrogen (N) management in many crops, including corn and cabbage. The use of a Cardy NO3 − meter to assess the N status of the carrot crop could improve the utilization of applied N, but critical NO3‐N concentrations are required. Two carrot cultivars were grown on mineral and organic soils over 3 years at five N application rates to establish critical sap and soil NO3‐N concentrations and to identify the effects of soil type and cultivar. Although a yield response to N application occurred on mineral soil in 2 of 3 years, consistent critical sap NO3‐N concentrations could not be established because of variability among years, cultivars, and soil types. Critical soil nitrate concentrations were highly variable, but values of 31 to 36 mg · L−1 NO3‐N could be established for the early sampling date to 30 cm deep. Sap NO3‐N concentrations cannot be used alone for N analysis of carrots, but early‐season soil NO3‐N assessment could be useful in adjusting N‐fertilization practices.

Nitrogen utilization timeline of carrot over the growing season

A timeline of nitrogen (N) dynamics of the carrot crop was developed based on studies on the effects of N application on carrot growth, N uptake and partitioning, and interactions with Alternaria [ALB; A. dauci (Kuhn) Groves and Skolko] and Cercospora [CLB; C. carotae (Pass.) Solheim] leaf blight. Preplant-applied fertilizer N affects yield only when residual N in the top 60 cm of the soil profile is insufficient. The majority of the N required by the crop is taken up beyond 50 d after seeding (DAS). Carrots have a root system that extends to 150-cm depth and >50% of the fibrous root system occurs below 30-cm depth. It is likely that N below 30 cm depth is required beyond 50 DAS, since the majority of the fibrous roots are below 30 cm depth after that stage. There is insufficient time for sidedressed N to leach into the active root system beyond 50 DAS, unless its application is timed before irrigation or rain events. Regardless of the amount of residual N, preplant-applied N is essential for minimizing l...

The effect of nitrogen on insect and disease pests of onions, carrots, and cabbage.

ABSTRACT Mineral nutrition may affect the ability of plants to resist harmful insects or diseases. The effects of nitrogen (N) nutrition on pests of onions (Allium cepa L.), carrots (Daucus carota L.), and cabbage (Brassica oleracea var. capitata L.) were evaluated on organic and mineral soils in Ontario, Canada in 2000 and 2001. Onions (cvs. Norstar and Winner) and carrots (cvs. Indiana, Idaho, and Annapolis) were grown on both soil types, and cabbage (cv. Atlantis) was grown on mineral soil. Nitrogen was applied at 0,50,100,150, and 200% (carrots and cabbage) and 0, 100, and 200% (onions) of the rate recommended by the Ontario Ministry of Agriculture, Food, and Rural Affairs using calcium ammonium nitrate preplant and potassium nitrate for sidedress applications. In cabbage, onion thrips (Thrips tabaci L.) damage was rated at harvest. Onion thrips (OT) populations were monitored in onions weekly. In carrots, the combined leaf blight symptoms caused by Cercospora carotae and Alternaria dauci was evaluated biweekly using a visual rating. The incidence and severity of cavity spot (Pythium spp.) was rated at harvest. The damage caused by OT was lower on cabbage that received 100–200% and 150% of the recommended N rate in 2000 and 2001, respectively, than the no N treatment in both years, and 200% of the recommended rate in 2001. This effect may have been due to delayed maturity of plants that received low and high N levels. Onion thrips populations in onions were not affected by N rate in either year or location. Leaf blight severity decreased with increasing N rate in most cases. There was no effect of N rate on cavity spot. Nitrogen management should be considered in the integrated pest/crop management program for cabbage, onions, and carrots.

Distribution of nitrogen uptake, fibrous roots and nitrogen in the soil profile for fresh-market and processing carrot cultivars

In temperate regions, yield of carrot [Daucus carota subsp. sativus (Hoffm.) Arkang.] is not generally affected by preplant applications of nitrogen (N). Previous studies speculate that carrots utilize N from much deeper in the soil profile than other crops. Carrot (cvs. Idaho and Fontana) were grown on organic and mineral soil in Ontario over a 3-yr period to determine rooting and N-uptake dynamics. Nitrogen application rates ranged from 0 to 200% of Ontario recommendations for each soil type. Soil samples collected at seeding and harvest at three depths were assessed for total N, nitrate-N and ammonium-N. The same cultivars were grown in 150-cm-deep PVC pipes filled with silica sand or soilless mix to assess root distribution and N uptake. Potassium nitrate fertilizer enriched with 15N was applied at three depths in the pipes and plants were assessed 28 d later for fertilizer N recovery. In the field, the highest N concentration both at seeding and at harvest was in the top 30 cm of the soil profile, bu...