A field experiment including daily fertilization and daily irrigation was conducted to study the growth and nitrogen dynamics of Phalaris arundinacea subjected to various moisture and fertilizer regimes. There were five treatments: Control 0 (C-0), neither fertilized nor irrigated; Control 1 (C-1), not irrigated and supplied with 15 g N m(-2) yr(-1) applied in a single dose in early spring; Irrigated (I-1), fertilized as described for C-1, but with daily irrigation; Irrigated/Fertilized 1 (IF1), received the same amount of nitrogen as C-1 and I-1, but supplied daily through a drip-tube system according to the predicted N demand of the crop; Irrigated/Fertilized 2 (IF2) was irrigated as I-1 and IF1, but received higher fertilizer doses, to eliminate any nutrient limitation. The above-ground crop was sampled 26 times between autumn 1992 and spring 1995. The in situ decomposition of crop residues was studied during 1993-1994. Nitrogen concentrations were measured in dry mass produced during the current year and decomposing residues from previous years' production. The loss of macronutrients from the crop between late autumn and the harvest time in early spring was calculated. The main differences in growth dynamics and yield between the treatments were due to irrigation. Growth was similar among the irrigated treatments. Crop biomass and nitrogen dynamics were similar in I-1 and IF1. Thus, the fertilizer regime did not affect crop growth or N amounts in the crop. Although crop nitrogen concentrations were highest in IF2, this did not result in higher crop production. Differences in growth dynamics between C-0 and C-1 were due to N fertilization. Differences in dry mass dynamics between 1993 and 1994 were explained by differences in temperature. The relatively cold May in 1994 retarded growth and decreased the crop's efficiency at converting radiation into biomass, even though N concentrations were almost twice as high in spring 1994 as in spring 1993. During the first year of establishment, about 0.4 kg dry mass m(-2) was produced. Under favourable conditions (fertilized and no water stress), 1.5 kg dry mass m(-2) was produced. However, during one winter, dry mass decreased by about 40% until harvest in spring. The main factor Limiting production was suggested to be low straw stiffness, which caused lodging, mainly in the irrigated treatments. Unless plant breeding can produce stiffer straw, the one-cut system will probably not be able to compete with other energy crops under intensive management at lower latitudes. The decomposition rates of crop residues were higher in the irrigated treatments than in C-0 and C-1. Nitrogen fertilization increased concentrations of N, P, K and S at harvest, and thus reduced the crop's quality as a biofuel. Changes in element concentrations during winter were minor and not consistent. However, concentrations of K were about 2.5 to 5 times lower in early spring than in the preceding autumns. (C) 1998 Elsevier Science B.V.
