Burning is a widely used in prairie management in the bluestem range of the Flint Hills (eastern Kansas to north-central Oklahoma, USA). In this study (undertaken near Manhattan, Kansas), the long-term effects of prescribed burns at different times of the year on chemical and physical properties of a loamy upland soil, were studied in livestock grazed and non-grazed areas.
Vegetation comprised primarily three native, warm-season perennial grasses, big bluestem Andropogon gerardi, little bluestem A.scoparius and indiangrass Sorghastrum nutans.
In 1926, an ungrazed unit was fenced and burning initiated within 10 (10.1 x 20.2 m) plots with five replicates per treatment (five burned annually and five biennially). Treatments (and approximate burn dates) were: winter (1 December), early spring (March 20), mid-spring (10 April) and late spring (1 May), and unburned (control). The study was suspended in 1944 but resumed in 1950, with all plots burned annually thereafter (to 1971).
The grazed unit was initiated in 1950 and divided into two: one area (44 acres; 17.8 ha) was burned annually from 1950 to 1971 in late spring; the second (60 acres; 24.3 ha) was unburned between 1950 and 1971. Both were stocked with yearling cattle at moderate rate (8 acre/animal unit) from 1 May to 1 October.
In November 1970, representative soil samples were taken with a hydraulic soil probe (3.8 cm diameter) to 1.22 m depth from all areas, and analysed for pH, organic matter, Ca, Mg, N, P and K.
The two tallgrass prairie areas burned annually for 20 (grazed) and 48 (ungrazed) years at different seasons of the year exhibited some differences in soil properties.
Winter, early-spring, and mid-spring burned ungrazed plots were generally higher in soil pH, organic matter and K than late-spring burned or unburned plots.
On ungrazed plots, winter burning caused most changes, with higher soil pH, organic matter, Ca, Mg, K, and lower soil N than with other treatments; late-spring burning had the least influence. Late-spring and winter burning also lowered soil N on grazed plots.
Although some difference in soil nutrient levels were statistically significant, these significant differences were so small that the authors consider it is unlikely that they are large enough to affect plant growth.
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