228
H. DAIJBENMIRE
exchttngeable (.!a in the upper 10-15 cm of the profile (Heyward, 1936;
Heyward arid Harnctte, 1934) and sometimes does the same for P, K and
Mg a N w d l (Metz et nl., 1961), but in general the improvement in nutrient
status as a consequence of regular burning is too small to be significant
(Heyward, 1036; Wahlenberg et aE., 1939; Suman and Carter, 1954).
Even though a grass fire in Iowa released sufficient bases to raise the
pH of the soil appreciably, no increase in exchangeable K could be
measured (Ehrenreich and Aikmnn, 1963). In B o u t e l m grassland of
southeastern Arizona fire decreased K consistently in the upper 25 mm
of the soil profile (Reynolds and Bohning, 1956).
4. A’itroye,,
A sninll reduction in the total N of the upper 38 mm of soil was reported in consequence of regular firing of Thenieda grassland in southern
Africa (Cook, 1939); the same was true in the upper 12 mm of a single
hot burn in Arteinisia steppe in eastern Idaho (Blaisdell, 1953). In the
Andropogon scoparius steppe of central Kansas no reduction of N could
be detected after 6 year8 of annual burning, regardless of the season
of burning (AldouB, 1934).
4n interesting aspect of the N problem has been developed by those
who compare the volatilization loss with the input from rainfall.
Accmrding to Grant’s et al. (1963) calculations for burning Molinia
grassland in Britain, fire a t intervals of 3 years would cause less loss of
N (and other nutrients, except possibly P) than the gains from precipitation. Also Hunter et al. (1!164), concluded that the input of nutrients
through rainfall is sufficient to balance the small outgo resulting from
both burning and removal of livestock from Molinia swards in Scotland.
In the Northern Territory of Australia 4-5 lb N/acre units is volatilized
when the grass cover is burned off. Since rainwater there supplies
2 lb/year and N fixation by microbes probably adds about an equal
amount, frequent grass burning would not seem to make a significant
drain on the total N reserve of the soil, which amounts to 3000 lb/acre
units in the root zone (Norman and Wetselaar, 1960). Standing in
marked contrast with the above, Elwell et al. (1941) calculated that
burning ungrazed grassland in eastern Oklahoma volatilizes 26.88 lb
N/acre units, and this represents a serious loss. In all such calculations
one must take into account that the N contained in litter is volatilized
completely only when the litter is entirely convertad to white ash. Any
charred litter remaining after the fire will contain 0.01-0.76% N, ovendryweight basis) that can materially increase the total N content of
the surface soil (Metz et al., 1961).
Whereas few investigators report’ significant loss of N from grass
fires, and others find burning neither detrimental nor beneficial, many
H. DAIJBENMIRE
exchttngeable (.!a in the upper 10-15 cm of the profile (Heyward, 1936;
Heyward arid Harnctte, 1934) and sometimes does the same for P, K and
Mg a N w d l (Metz et nl., 1961), but in general the improvement in nutrient
status as a consequence of regular burning is too small to be significant
(Heyward, 1036; Wahlenberg et aE., 1939; Suman and Carter, 1954).
Even though a grass fire in Iowa released sufficient bases to raise the
pH of the soil appreciably, no increase in exchangeable K could be
measured (Ehrenreich and Aikmnn, 1963). In B o u t e l m grassland of
southeastern Arizona fire decreased K consistently in the upper 25 mm
of the soil profile (Reynolds and Bohning, 1956).
4. A’itroye,,
A sninll reduction in the total N of the upper 38 mm of soil was reported in consequence of regular firing of Thenieda grassland in southern
Africa (Cook, 1939); the same was true in the upper 12 mm of a single
hot burn in Arteinisia steppe in eastern Idaho (Blaisdell, 1953). In the
Andropogon scoparius steppe of central Kansas no reduction of N could
be detected after 6 year8 of annual burning, regardless of the season
of burning (AldouB, 1934).
4n interesting aspect of the N problem has been developed by those
who compare the volatilization loss with the input from rainfall.
Accmrding to Grant’s et al. (1963) calculations for burning Molinia
grassland in Britain, fire a t intervals of 3 years would cause less loss of
N (and other nutrients, except possibly P) than the gains from precipitation. Also Hunter et al. (1!164), concluded that the input of nutrients
through rainfall is sufficient to balance the small outgo resulting from
both burning and removal of livestock from Molinia swards in Scotland.
In the Northern Territory of Australia 4-5 lb N/acre units is volatilized
when the grass cover is burned off. Since rainwater there supplies
2 lb/year and N fixation by microbes probably adds about an equal
amount, frequent grass burning would not seem to make a significant
drain on the total N reserve of the soil, which amounts to 3000 lb/acre
units in the root zone (Norman and Wetselaar, 1960). Standing in
marked contrast with the above, Elwell et al. (1941) calculated that
burning ungrazed grassland in eastern Oklahoma volatilizes 26.88 lb
N/acre units, and this represents a serious loss. In all such calculations
one must take into account that the N contained in litter is volatilized
completely only when the litter is entirely convertad to white ash. Any
charred litter remaining after the fire will contain 0.01-0.76% N, ovendryweight basis) that can materially increase the total N content of
the surface soil (Metz et al., 1961).
Whereas few investigators report’ significant loss of N from grass
fires, and others find burning neither detrimental nor beneficial, many