STUDIES ON FERTILIZER NITROGEN AND CUTTING MANAGEMENT OF SOWN GRASS AND LEGUME PASTURES IN PURE AND MIXED SWARDS

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Department of Agriculture

STUDIES ON FERTILIZER NITROGEN AND CUTTING MANAGEMENT OF SOWN GRASS AND LEGUME PASTURES IN PURE AND MIXED SWARDS

The experiment was a 3 x 3 x 2 factorial laid out in a randomized complete block
design with three replications. Treatments comprised three swards types (pure grass, pure
legume and grass-legume mixed swards), three harvesting frequencies of 4-, 8-, and 12-
weekly intervals and two levels of nitrogen at 0, and 300 kg N ha-1. The third experiment
was conducted to evaluate the effects of two cutting frequencies (4- and 8-weekly
intervals) on the growth and yield of four legumes (Lablab purpureus, Stylosanthes
hamata, Centrosema pascuorum and Stylosanthes guyanensis) and four grasses (Sorghum
almum, Panicum maximum, Chloris gayana and Andropogon gayanus). Basal applications
of muriate of potash (75 kg K ha-1) and single superphosphate (44 kg P ha-1) were also
made by broadcasting in all the experiments. In the first experiment, tiller number per
square metre, plant height and grass dry matter yield were increased by 44%, 6% and
53%, respectively, during the establishment year when fertilizer-N rate was increased from
0 to 450 kg N ha-1. Grass dry matter yield was increased by 41% and 149% when the
interval between cuts was increased from 3- to 12-weekly intervals at the first and fourth
harvest years, respectively.

Plots cut at 3- or 6- weeks intervals exhibited much greater
weed proportion than those cut 9-, or 12-weekly intervals. Increasing the interval between
harvests from 3 to 12 weeks increased the proportion of stem relative to leaf blade in the
grass swards. The proportion of inflorescence, plant height and dry matter percentages,
were generally increased by increasing the interval between cuts. Tiller number decreased
with increasing interval of cut. The total annual herbage dry matter yield was increased by
32% and 48% in 2001 and 2004, respectively, when fertilizer-N was increased from 0 to
450 kg N ha-1. Increasing the N rate from 0 to 450 kg N ha-1 increased the proportion of
stem relative to the leaf blade in the grass swards. Plant height and tiller number were
increased with increase in N application while the dry matter percentage was generally
decreased with incremental application of nitrogen. A combination of 12-weekly interval
of cut with 300 kg N ha-1 gave a significantly higher forage grass herbage dry matter yield
compared with the values got from the 3- or 6-weekly interval combined with any N rate.
Fertilizing at 300 or 450 kg N ha-1 when combined with cutting at 9 or 12-weekly interval
between cuts was more effective in suppressing weed growth and weed dry matter as a
proportion of the total herbage dry matter. The N % and crude protein contents in the leaf,
stem and in total herbage dry matter decreased significantly with increasing interval
between cuts. Yield of crude protein in the total herbage was significantly higher when
cutting was done every 6 weeks compared with when done every 9 weeks. Nitrogen
fertilizer x cutting frequency interaction effects on N %, crude protein contents and crude
protein yields in the crop fractions and in total herbage dry matter were not statistically
significant. On the average, the crude protein and mineral contents were higher in the leaf
fraction than in the stem and inflorescence fractions. In the second experiment, herbage
production was 16% and 69% higher on guinea grass/stylo swards in 2006 and 2007,
respectively, compared with the yields for the pure guinea grass swards. Grass dry matter
yield as a proportion of the total herbage dry matter was significantly increased from 45%