STUDIES ON FERTILIZER NITROGEN AND CUTTING MANAGEMENT OF SOWN GRASS AND LEGUME PASTURES IN PURE AND MIXED SWARDS
ABSTRACT
Three field experiments were conducted at the Teaching and Research Farm of the
Department of Crop Science, Faculty of Agriculture, University of Nigeria, Nsukka. In the first experiment, the effects of fertilizer-N application and cutting management on
establishment, growth and yield of guinea grass (Panicum maximum) were investigated. The experiment was a 4 x 4 factorial laid out in a randomized complete block design with three replications. Treatments comprised four levels of Nitrogen of 0, 150, 300, and 450kg N ha-1 and four harvesting frequencies of 3-, 6-, 9- and 12-weekly intervals. A second experiment was conducted using guinea grass/verano stylo (Stylosanthes hamata) mixedswards.
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.
