Influences of Sources and Rates of Nitrogen Fertilizers on Para Grass Brachiaria mutica (Forsk.) Stapf Grown in the Central Part of Thailand

Abstract

Pot experiment was established to determine the influences of three nitrogen sources (ammonium sulfate, ammonium chloride and urea) and five nitrogen rates (0,O. 64,1.28,1.92 and 2.56 gNlpot or 0,40,80,120 and 160 kgN1rai) on oven-dry forage yields, N yields and N recovery of para grass grown on Nakhon Pathom, Kamphaeng Saen, Muak Lek and Chai Badan soil series. These four soil series were the most common soils used for growing forage crops for dairy production in the western and central parts of Thailand. The experiment was conducted at Kasetsart University (Bangkhen campus) for a period of six months. Oven-dry forage yields and N yields of para grass grown on all soil series applied with different sources of N fertilizer were the highest at N rate of 2.56 gNlpot, but the highest response per unit of N fertilizer used were found at the rates ranged from 0.64 - 1.28 gN1pot. Oven-dry forage yields were increased at the same amount from all N sources and all of the soil series except Muak Lek soil, when fertilizer N were applied at low rate (0.64 gN1pot). However, oven-dry forage yields from urea N source were lower than those from other N sources when fertilizer N were applied at higher rate (1.28 - 2.56 gN1pot) on all of the soil series except Nakhon Pathom soil series which is acid soil. Oven-dry forage yields and N yields of para grass grown on Muak Lek soil series were the highest when fertilizer N were not applied. But oven-dry forage yields and N yields of para grass grown on Chai Badan soil series gave the highest response to all rates of fertilizer N. Recovery of fertilizer N in oven-dry forage yields from all soil series was the highest from ammonium sulfate N source and the lowest from urea N source. Average recovery of fertilizer N in over-dry forage yields grown on Nakhon Pathom (60%), Chai Badan (58%) and Kamphaeng Saen (55%) soil series were higher than that from Muak Lek (44%) soil series.