Broccoli Plant Nitrogen, Phosphorus, and Water Relations at Field Scale and in Various Growth Media

Abstract

High-value broccoli (Brassica oleracea var. italica L.) plant nutrition and water relations are not well understood. Our objectives were to examine the relations of plant nitrogen (N) and phosphorus (P) translocation and water holding in direct-seeded broccoli (cv. Everest) under different postseeding N treatments at field scale and with different growth media types and water supply levels under greenhouse conditions. A 2-year field study was conducted in a moderately drained Woodville loam in 2007 and in a poorly drained Lawrence loam in 2008. The field experimental treatments were the postseeding N rates of 0, 25, 50, 75, and 100 kg·ha−1, arranged with four blocks in a randomized complete block design. The greenhouse study treatments consisted of two growth media types, mineral soil (MS) and peat-based Promix (PP), and two water supply levels, 15% (W15) and 30% (W30), of the growth media weights, arranged with eight replicates in a completely randomized design. Results showed that the main effect of the postseeding N treatments was significant on broccoli head size (P < 0.0167). Block effects and the N treatment linear effects were significant on leaf/stem N and head N/P accumulation, broccoli yield, and head size (P < 0.05). Broccoli yield and head size were correlated with whole plant water holding, leaf/stem N, and head N/P accumulation (P < 0.05). In the greenhouse, broccoli leaf N/P accumulation, leaf chlorophyll, and whole plant biomass were significantly higher in the MS than in the PP (P < 0.0182). The interaction between growth media and water supply was significant on leaf P% and leaf N accumulation (P < 0.0027). It is suggested that mineral soil growth media, water supply at half field capacity (W15), and postseeding N inputs are important factors for promoting plant water holding and N/P translocation within plants to improve broccoli head development, and its sink/source relations.