Relationship between growth and N:P of cabbage (Brassica oleracea L., var. capitata) plug seedlings according to moisture content and nitrogen and phosphorus application after transplanting

The aim of this study was to evaluate the effect of moisture on N and P uptake of cabbage (Brassica oleracea L., var. capitata) and to determine whether relative growth rate (μ) is correlated to either the concentration of N (NP), P (PP), or their ratio (NP:PP) in shoots. Seedlings were transplanted and exposed to different levels of moisture, N and P under controlled conditions. μ, leaf area, NP, and PP were determined and the relationship between μ and NP, PP, and NP:PP were examined using generalized linear models. Increased moisture levels enhanced the uptake of both N and P. A larger N supply increased μ and NP but tended to decrease PP, whereas a larger P supply increased PP but had little effect on μ and NP. NP:PP could be predicted from individual N and P supply or from their ratio. The regulatory coefficient (H value) of cabbage seedlings, expressing the extent of homeostasis, was estimated as 4.10, which is relatively high among herbaceous plants. μ and NP were highly correlated, whereas PP and NP:PP did not show a significant relationship to μ. We concluded that nutrient uptake can be enhanced by moisture management, and that μ is highly correlated to NP while there was a weak relationship between μ and NP:PP in cabbage seedlings because of the relatively strong homeostasis.