GROWTH AND NITROGEN DYNAMICS OF REED CANARYGRASS (PHALARIS-ARUNDINACEA L.) SUBJECTED TO DAILY FERTILIZATION AND IRRIGATION IN THE FIELD

A field experiment including daily fertilization and daily irrigation was conducted to study the growth and nitrogen dynamics of Phalaris ar undinacea subjected to various moisture and fertilizer regimes. There were five treatments: Control 0 (C-0), neither fertilized nor irrigate d; 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), fertilize d as described for C-1, but with daily irrigation; Irrigated/Fertilize d 1 (IF1), received the same amount of nitrogen as C-1 and I-1, but su pplied daily through a drip-tube system according to the predicted N d emand of the crop; Irrigated/Fertilized 2 (IF2) was irrigated as I-1 a nd IF1, but received higher fertilizer doses, to eliminate any nutrien t limitation. The above-ground crop was sampled 26 times between autum n 1992 and spring 1995. The in situ decomposition of crop residues was studied during 1993-1994. Nitrogen concentrations were measured in dr y mass produced during the current year and decomposing residues from previous years' production. The loss of macronutrients from the crop b etween late autumn and the harvest time in early spring was calculated . The main differences in growth dynamics and yield between the treatm ents were due to irrigation. Growth was similar among the irrigated tr eatments. Crop biomass and nitrogen dynamics were similar in I-1 and I F1. Thus, the fertilizer regime did not affect crop growth or N amount s in the crop. Although crop nitrogen concentrations were highest in I F2, this did not result in higher crop production. Differences in grow th dynamics between C-0 and C-1 were due to N fertilization. Differenc es in dry mass dynamics between 1993 and 1994 were explained by differ ences in temperature. The relatively cold May in 1994 retarded growth and decreased the crop's efficiency at converting radiation into bioma ss, even though N concentrations were almost twice as high in spring 1 994 as in spring 1993. During the first year of establishment, about 0 .4 kg dry mass m(-2) was produced. Under favourable conditions (fertil ized 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 st raw stiffness, which caused lodging, mainly in the irrigated treatment s. Unless plant breeding can produce stiffer straw, the one-cut system will probably not be able to compete with other energy crops under in tensive 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 h arvest, and thus reduced the crop's quality as a biofuel. Changes in e lement concentrations during winter were minor and not consistent. How ever, concentrations of K were about 2.5 to 5 times lower in early spr ing than in the preceding autumns. (C) 1998 Elsevier Science B.V.