Effects of late spring burning and nitrogen fertilization on nutritive values of big and little bluestem plants

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Introduction
Both increasing populations and per capita consumption of beef in the United States and in other countries call for new management practices to increase the carrying capacity of native rangelands.
It has long been recognized that annual late-spring burning of True Prairie rangelands stimulates beef cattle performance.Commercial fertilizers also have been used to increase production of cultivated crops but such use on native prairies has been questionable.
Reported here are how annual late-spring burning and nitrogen fertilization, separately and together, affect nutritive values of Big and Little Bluestem, two primary grass species of the True Prairie.

Experimental Procedure
The study was conducted during the 1972 growing season on native True Prairie rangeland near Manhattan, Kansas.Four pastures varied in size from 44 to 60 acres were involved.
Samples of two species of grass, Big Bluestem and Little Bluestem, were collected on loamy upland range.
One of four treatments was applied to each pasture to evaluate effects of annual late-spring burning and nitrogen fertilization on the nutritive value of bluestem grass.
Burning.Burning was April 28 with a light northern breeze.All organic matter was consumed by the fire.
Nitrogen.Nitrogen in the form of granular urea was aerially applied May 17 at 40 pounds of nitrogen per acre.
Burning and Nitrogen.Burning and nitrogen fertilization were as just indicated.

Control. No burning or fertilization.
The grass samples were clipped at ground level from within 25-foot square exclosures in three randomly located, loamy upland sites in each pasture.The exclosures were constructed with "T" type steel posts and 4 strands of barbed wire.
Three samples were taken from each pasture on the first of each month, June to November.
Preparation for analysis consisted of drying overnight at 90° C in a forced air oven and grinding in a Wiley mill through a one-millimeter screen.

Results
Burning significantly decreased the dry matter content of the bluestem grass in June, September, and November (Table 1).In July and October there were no significant differences.Although not shown, fertilization and fertilization plus burning had no additional effect on the dry matter content of the grass.No species differences were detected.

Crude Fiber
Table 1 shows the crude fiber content of the bluestem grass.The general trend is for crude fiber to gradually increase as the growing season advances.The August 1 clipping showed a decline in the fiber content of the grass.Increased production of new plant tissue (low in crude fiber) after 2.54 inches of rainfall in July may explain the fiber decline.
Burning significantly lowered the crude fiber content of the grass throughout the study period (Table 1).That likely explains why beef cattle on burned range outperforms cattle on range not burned.Although not shown, fertilization had no effect on crude fiber content of the grass.

Cell Walls
Cell wall percentages followed the same trend as crude fiber (Table 2).Cell walls increase as the season advances.Burning compared to not burning significantly decreased cell wall percentages June through August; no differences were detected in the September or October clippings but the burned pastures had significantly lower cell wall percentages in November than the nonburned pastures did.
As with crude fiber, Big Bluestem had significantly lower percentages of cell walls than Little Bluestem did.Table 2 shows cell wall percentages for each species during the study.Big Bluestem was consistantly lower.Although not shown, fertilization did not influence cell wall percentages.

Protein
Table 3 shows effects of treatment on protein levels of the grass.Burning or fertilization alone did not significantly affect protein levels but burning and fertilization together significantly increased protein content.This difference was only a .57%and of little practical importance.
Table 4 shows the average protein levels at monthly intervals throughout the study.The protein levels dropped from 11.62% in June to 2.89% in November.

Lignin
The average lignin content of the bluestem grass is shown in Table 5. Lignin gradually increases as the growing season advances.Both burning and fertilization significantly influenced lignin content of the grass plant (Table 6).

Table 1 .
Dry Matter and Crude Fiber Percentages of Big and Little Bluestem grass (Combined dry matter basis), June l-November 1, 1972.

Table 5 .
Percent Lignin in Bluestem Grass by Months June-November, 1972