Net assimilation rate of some C3 grasses over vegetative period

As the previous studies of the growth of grassland were focused on seminatural grassland we decided to analyse the growth process of the temporary grassland cultivated on arable land as a monoculture of individual grass species. Field trials included three grass species (Lolium perene L., Lolium multiflorum Lam. and Festuca arundinacea Schreb.) and three intergeneric hybrids were established in a cold and humid montaine region of eastern Slovakia (Matejovce, elevation 700 m, mean daily temperature 12.7 deg C and rainfall of 408.3 mm per growth period). Area of individual plots was 10 square m (four replicates) and seeding rate was 35 kg/ha (rows of 125 mm, sowing depth 20-30 mm). The first doses of nitrogen (30 kg N/ha) and phosphorus with potassium (30 and 60 kg/ha) were applied in spring, the remaining nitrogen doses (2x30 kg N/ha) after the first and second cut. The plots were cut three-times over the growth period. The chlorophyll a+b concentration (SPAD values) was determined by a hand-held chlorophyllmeter SPAD-502 (Minolta, Japan). Twenty mature leaves were taken in the morning (08.00 - 09.00 hour) on the day of cutting. Ten leaves were used for the measurent of SPAD values (20 measurements along the side of the leaf blades). After drying the leaves (24 hours, 105 deg C ) in a laboratory dryer the material was used for determination of nitrogen in dry leaf matter (CHN analyser, Carlo-Erba, Italy). The net assimilation rate was determined on the differences of dry matter weight and leaf area between the beginning and the end of individual growth periods (three cuts) according to the following formula NAR = W2 _ W1 (1n A sub(2) - 1n A sub(1)):A sub(2) _ A sub(1).(t sub(2) _ t sub(1)) where _ W - dry matter weight of aboveground part A - leaf area t _ time Index 1 indicates individual values at the beginning of growth period (W sub(1), A sub(1), t sub(1)), index 2 values at the end of growth period (W sub(2), A sub(2), t sub(2)) The samples were taken from the area of 250 x 250 mm (four replicates) close above soil level. The averages, standard deviations and correlation co-effitients were calcultated from results. Results confirmed an average NAR of studied grass assortment of 2.0 gper square m per day. The decline of NAR from the spring to the autumn (from the 1st to the 3rd cut) was confirmed, namely (average of all cultivars) 3.26 1.48 1.27 g per square m per day. Tall fescue and both cultivars of annual ryegrass were characterised by the highest net assimilation rates. Smaller values were typical for intergeneric hybrids and perennial ryegrass. Remarkable differences in leaf characteristics were confirmed among analysed grass assortment. In the summer period of growth the reduction of all leaf traits except nitrogen concentration were confirmed (summer depression). A decline in NAR in this period was also detected. A close correlation (r = 0.836++) between chlorophyll a + b concentration (SPAD values) and leaf nitrogen concentration was confirmed.