Abstract
A field trial in Northeast Thailand during 2011–2012 compared the effects of nitrogen fertilizer, applied as urea in the wet season, on the growth and quality of Panicum maximum cvv. Mombasa and Tanzania. In the establishment year, increasing rates of nitrogen (0, 20, 40 and 60 kg N/ha every 40-45 days) (0–180 kg N/ha for growing period) progressively increased stem, leaf and total DM production (P<0.05). At higher rates (80 and 100 kg N/ha or 240–300 kg N/ha for growing period), only total DM increased at the highest rate. In the second year, a rate of 20 kg N/ha every 40-45 days (80 kg N/ha for growing season) doubled the amount of DM compared with no nitrogen, and 80 kg N/ha every 40-45 days (320 kg N/ha for growing period) produced significantly higher stem, leaf and total DM yields than most other rates. The yield response (kg DM/kg N) decreased linearly (24.7 to 20.3 in 2011; 56.7 to 15.1 in 2012) from the lowest to the highest rate of nitrogen. In both years, increasing rates of nitrogen significantly increased CP and NDF concentrations in stems and leaves and ADF concentrations in stems. Mombasa produced 17 and 19% more leaf and 18 and 22% more total DM than Tanzania, in the first and the second year, respectively. Mombasa also produced 30% more stem DM than Tanzania in the second year. While Tanzania produced higher CP levels than Mombasa in the establishment year, in the second year, Tanzania had higher levels than Mombasa only when N rates of 80–100 kg N/ha were applied every 40-45 days (320–400 kg N/ha for growing period). Applying 60 kg N/ha every 40-45 days appears to be a reasonable compromise to achieve satisfactory DM yields in the wet season (8,000 kg/ha first year and 12,000 kg/ha second year), leaf percentage of 68–70% and leaf CP concentrations above 7%.Keywords: Guinea grass, crude protein, leaf production, fertilizer responses.DOI: 10.17138/TGFT(3)27-33
Highlights
Pastures in Northeast Thailand are usually grown on the poorest soils, as more fertile soils are used for growing food and cash crops
This study has shown that applying 40–60 kg N/ha to guinea grass every 40–45 days during the wet season will more than double the dry matter (DM) yield over that of unfertilized pasture
While these responses are outstanding, they are much lower than the increases of up to 250% recorded by Hare et al (1999), when 20 kg N/ha was applied to Paspalum atratum on similar soils in Northeast Thailand every 30 days
Summary
Pastures in Northeast Thailand are usually grown on the poorest soils, as more fertile soils are used for growing food and cash crops. The exceptions are the larger commercial dairy farms (about 1,000 larger farms, milking on average 100 cows with an average size of 20 ha) and small village farmers, who grow guinea grass for sale as fresh forage In both of these systems, fertilizer is applied at rates of 10–20 kg N/ha 3– 6 times in a wet season or when irrigated in the dry season (Udchachon et al 1998; Nakamanee et al 2008). Under intensive cutting every 30–40 days for the sale of fresh forage in Northeast Thailand, Tanzania guinea grass produced DM yields of 33–46 t/ha/yr (Nakamanee et al 2008) In this system, farmers applied 125–310 kg urea/ha (46% N) or 160–310 kg NPK/ha (16:7:6) after each cut, a total of approximately 500–1,000 kg N/ha/yr. Poultry manure at a rate of 2.8–5.6 t/ha was applied every 60–90 days
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