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Publication Date
1981
Description
In the region of Mediterranean-type climate in California, brush is converted to grassland to reduce fire hazards, increase feed for herbivores, and increase water yields. There is little information on how this change of cover type affects soil fertility over a long period. Research was initiated to measure the long-term effect of converting brush to grass on the availability of nutrients in the soil. In 1956 chaparral growing on Los Gatos soil (fine-loamy, mixed mesic family of typic argixerolls) was crushed, burned, and seeded to grasses and clovers, and half the area was fenced to exclude herbivores. Sprouting brush either was treated periodically by burning or with herbicides or was not treated at all. Twenty-three years after the initial burn, about 3 % of the cover on reburned plots was brush, virtually none was brush where herbicides were used, and nearly 100% was brush where nothing was done to control regrowth. Herbaceous plants were abundant where brush sprouts had been controlled. Soil samples were taken from the six treatments for chemical analysis and a pot experiment. Soft chess (Bromus mollis L.) was grown in pots fertilized with all combinations of nitrogen (N), phosphorus (P), and sulfur (S). The plants were analyzed for N, P, S, potassium (K), calcium (Ca), and magnesium (Mg). In the pot study, uptake of N, P, K, S, Ca, and Mg was greater from soils where brush regrowth was controlled than from soils where brush had regrown. These differences were much greater for soils under grazing. Extractable nutrients in the soils from the grazed area were also higher from grassland plots than from brush plots. The grazed grasslands had 81 % ground cover by living plants, of which 14% was annual legumes, 25% annual grasses, 30% Erodium spp., and 11 % perennial grasses. The ungrazed plots had 25% ground cover and only 3% legumes, 7% annual grasses, 1 % Erodium spp., and 9% perennial grasses. Nutrient availability was greater after a 23-year period in brush-soil converted to grassland than where brush regrew, and this difference in soil fertility was enhanced by grazing. The difference in soil fertility on the grazed grassland plots may be due to (1) the shallower, more fibrous root systems of grassland species (as compared with brush) resulting in a retention of mineral nutrients in the surface soil; (2) increased rate of cycling, and thus nutrient availability, due to grazing animals; (3) the contribution of annual legumes to soil N; and ( 4) a reduction in surface-soil erosion, there being much bare soil and an erosion pavement under the brush.
Citation
Jones, M B.; Koenigs, R L.; Vaughn, C E.; and Murphy, A H., "Effect of Converting Chaparral to Grassland on Soil Fertility in a Mediterranean-Type Climate" (1981). IGC Proceedings (1981-2023). 5.
(URL: https://uknowledge.uky.edu/igc/1981/section3/5)
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Effect of Converting Chaparral to Grassland on Soil Fertility in a Mediterranean-Type Climate
In the region of Mediterranean-type climate in California, brush is converted to grassland to reduce fire hazards, increase feed for herbivores, and increase water yields. There is little information on how this change of cover type affects soil fertility over a long period. Research was initiated to measure the long-term effect of converting brush to grass on the availability of nutrients in the soil. In 1956 chaparral growing on Los Gatos soil (fine-loamy, mixed mesic family of typic argixerolls) was crushed, burned, and seeded to grasses and clovers, and half the area was fenced to exclude herbivores. Sprouting brush either was treated periodically by burning or with herbicides or was not treated at all. Twenty-three years after the initial burn, about 3 % of the cover on reburned plots was brush, virtually none was brush where herbicides were used, and nearly 100% was brush where nothing was done to control regrowth. Herbaceous plants were abundant where brush sprouts had been controlled. Soil samples were taken from the six treatments for chemical analysis and a pot experiment. Soft chess (Bromus mollis L.) was grown in pots fertilized with all combinations of nitrogen (N), phosphorus (P), and sulfur (S). The plants were analyzed for N, P, S, potassium (K), calcium (Ca), and magnesium (Mg). In the pot study, uptake of N, P, K, S, Ca, and Mg was greater from soils where brush regrowth was controlled than from soils where brush had regrown. These differences were much greater for soils under grazing. Extractable nutrients in the soils from the grazed area were also higher from grassland plots than from brush plots. The grazed grasslands had 81 % ground cover by living plants, of which 14% was annual legumes, 25% annual grasses, 30% Erodium spp., and 11 % perennial grasses. The ungrazed plots had 25% ground cover and only 3% legumes, 7% annual grasses, 1 % Erodium spp., and 9% perennial grasses. Nutrient availability was greater after a 23-year period in brush-soil converted to grassland than where brush regrew, and this difference in soil fertility was enhanced by grazing. The difference in soil fertility on the grazed grassland plots may be due to (1) the shallower, more fibrous root systems of grassland species (as compared with brush) resulting in a retention of mineral nutrients in the surface soil; (2) increased rate of cycling, and thus nutrient availability, due to grazing animals; (3) the contribution of annual legumes to soil N; and ( 4) a reduction in surface-soil erosion, there being much bare soil and an erosion pavement under the brush.
