Broccoli growth in response to increasing rates of pre-plant nitrogen. II. Dry matter and nitrogen accumulation

Abstract

An understanding of plant nitrogen accumulation and soil nitrogen dynamics is needed to develop management practices that balance nitrogen requirements of vegetable crops with environmental protection. Field trials were conducted in 2001 and 2002 to determine the interaction of increasing rates of pre-plant nitrogen fertilizer with broccoli tissue nitrogen accumulation and soil nitrogen dynamics. Broccoli cultivars Decathlon and Captain were grown with seven rates of nitrogen (0, 50, 100, 150, 200, 300, 400 kg N ha-1) applied pre-plant as ammonium nitrate. Rate of nitrogen accumulation by the above-ground tissue biomass varied over time and among nitrogen treatments, ranging from 1 to 16 kg N ha-1 d-1. At harvest, tissue nitrogen was high, but nitrogen use efficiency was low when high rates of nitrogen were applied. Soil NO3--N content decreased from planting to harvest. At harvest, soil NO3--N increased with increasing rates of nitrogen, with the majority of NO3--N found in the top 0 to 30 cm of the soil. At 200 kg ha-1 applied nitrogen, plants recovered essentially all of the estimated available nitrogen and there appears to be little risk of nitrogen loss during the growing season. Approximately 130 kg N ha-1 was supplied by the soil during the cropping season. Soil and crop residues at harvest ranged from 96 to 330 kg N ha-1. This residual fertility poses a risk for nitrogen loss. Practical and cost-effective strategies are needed to manage residual nitrogen in the soil and crop residues to minimize loss and retain this nitrogen for subsequent crops. Key words: Brassica oleracea L. italica Plenck, nitrogen budget, nitrogen rates, nitrogen use efficiency, nutrient management

Broccoli growth in response to increasing rates of pre-plant nitrogen. I. Yield and quality

“…This result is likely related to a slower rate of head expansion associated with reduced dry matter accumulation at the low rates of nitrogen (Bakker et al 2009). A significant year by cultivar interaction was also observed for the time to 50% harvest (P00.0037).…”

“…Hence, determining the ''optimum'' amount of nitrogen to apply to a crop poses a complex question. Some of these issues are discussed in more detail in Bakker et al (2009), but many are beyond the scope of a single study.…”

“…Plant dry matter, nitrogen accumulation and residual nitrogen in the soil and crop residues as a function of these fertilizer treatments are reported in Bakker et al (2009).…”

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

“…Nitrogen fertilizer applications are frequently used to enhance vegetable crop production, and much research has been done to reduce N losses during the vegetable crop growing season [1,2]. However, after harvest, a large quantity of N can remain in vegetable crop residues [2][3][4], which readily mineralizes [3] and may be susceptible to post-harvest losses.…”

“…Cole crop 1 in the field at harvest [2,3], and post-harvest mineral N losses are more related to crop residue N rather than N fertilizer remaining in the soil [3]. Considering that 35 to 60% of broccoli crop residue N has been found to mineralize in controlled incubation studies [10,11], and that the crop residue may contain up to 330 kg N ha 1 [1], then up to 198 kg N ha 1 would be mineralized in the field after harvest from broccoli crop residue [11]. Thus, cole crop residue poses a significant risk for N losses due to the large quantity of mineralizable N in the post-harvest season.…”