Evaluation of Post-Harvest Organic Carbon Amendments as a Strategy to Minimize Nitrogen Losses in Cole Crop Production

Abstract

Abstract:Cole crops (Brassica vegetables) can pose a significant risk for N losses during the post-harvest period due to substantial amounts of readily mineralizable N in crop residues. Amending the soil with organic C has the potential to immobilize N and thereby reduce the risk for N losses. Four field trials were conducted to determine the effects of organic C amendments (OCA) on N dynamics and spring wheat (Triticum durum L.) harvest parameters proceeding early-and late-broccoli (Brassica olecerea var italica L.) systems in 2009 and 2010. The experimental controls represented the traditional grower practice of incorporated broccoli crop residue (CR-control) and the pre-plant application of N fertilizer (CRN-control) to subsequent spring wheat. Alternative practices were compared to the controls, which included broccoli crop residue removal (CR-removal), an oat (Avena sativa L.) cover crop (CC-oat), and three different OCA of wheat straw (OCA-straw), yard waste (OCA-yard), or used cooking oil (OCA-oil). The treatments, which demonstrated reduced autumn soil mineral N (SMN) concentrations after broccoli harvest, relative to the CR-control, were CR-removal, OCA-straw, and OCA-oil. Although CR-removal and OCA-straw indicated a reduced potential for autumn soil N losses in the early-broccoli system, these practices are not recommended for growers because subsequent spring wheat yield and profit margins were reduced compared to the CR-and CRN-controls. The OCA-oil reduced autumn SMN concentrations by 53 to 112 kg N ha relative to the CR-control after both early-and late-broccoli harvest, suggesting a larger potential for reduced autumn soil N losses, compared to all other treatments. No detrimental effects resulted from the OCA-oil OPEN ACCESSAgronomy 2013, 3 182 treatment on the subsequent spring yield or grain N. The OCA-oil reduced spring wheat profit margins relative to the CR-control, like the OCA-straw and CR-removal treatments, however profit margins were similar between the OCA-oil and the CRN-control. Therefore, in areas with a high risk of environmental N contamination, growers should consider the OCA-oil practice after cole crop harvest to minimize the risk of N losses.

Nitrogen cycling and management in intensive horticultural systems

“…However, cole crops can be harvested as late as November in temperate regions, which leaves little time for cover crop establishment. Both Nett et al (2011) and Congreves et al (2013b) found little evidence that cover crops reduced N losses after cauliflower or broccoli production, respectively. In order to overcome this limitation, Everaarts (1993) encouraged growers to undersow cover crops between the rows of a cole crop prior to harvest.…”

“…Crop residue removal reduced SMN concentrations and potential N loss after broccoli harvest (Congreves et al 2013b), but most crop residue removal studies have focused on field crops, as reviewed by Agneessens et al (2014). Therefore more research is needed on the impact of crop residue removal in horticultural systems.…”

“…leaves), soil mineral N contents of 89-227 kg ha -1 were observed during the fall after harvest in the 0-30 cm depth (Congreves et al 2013b). It was hypothesized that the high soil mineral N concentrations were due to residual fertilizer N or root biomass N (Congreves et al 2013b); however, a subsequent 15 N tracer study found indigenous soil mineralization during autumn produced a greater source of N than residual fertilizer or broccoli roots after crop harvest ). Overall, Congreves et al (2014) demonstrated that the relative importance of the sources of N susceptible to post-harvest loss was: crop residue N (stem ?…”

“…If processers and growers test for the N content of crop yields (rather than labour and cost intensive tests for entire plant), informed risk assessments for potential N loss after harvest can be derived by using the presented equation (1). Soil mineral N levels can often be elevated after vegetable harvest (Congreves et al 2013b;Bakker et al 2009a), either as a result of fertilizer N application at rates exceeding crop requirements or as a result of mineralization. For example, after removing aboveground broccoli crop residue (stem ?…”

Nitrogen Related Diffuse Pollution from Horticulture Production—Mitigation Practices and Assessment Strategies

“…This means that when assessing the risk of post-harvest losses, the N content in the crop residues must be considered in addition to the potential for soil OM mineralization. Up to 198 kg·N·ha −1 may result from leaving broccoli crop residues in the field after harvest, representing a significant risk [69]. This situation may occur mainly for brassica crops, which are the ones with higher N contents (Table 1).…”