The purpose of the study was to evaluate 3 strains of switchgrass (Panicum virguturn L.) under 3 water and 3 harvest regimes. Dry matter yields, under natural rainfall and full irrigation, averaged 2.0 and 6.7 metric tons/ha, respectively. Productivity of the 3 strains ranked G 3OO>HV-341>Biackweii. Yields of HV-341 and Blackwell were similar under 1,2, or 3 harvests per year but those of G-300 were reduced by 2 or 3 harvests. Switchgrass forage contained about 10.8% crude protein (CP) and 0.23% P in late June. In November, previously unclipped forage contained 4.3% CP and 0.12% P, while that clipped twice contained 5.5% CP and 0.15% P. Maximum production was obtained with 116.5 cm of water use but maximum water use effhziency was obtained with about 85.5 cm of water use (rainfall f irrigation + soil water), The switchgrasses are adapted for use both without irrigation and when varying amounts of irrigation water are availbie. G-300 yielded more and produced earlier and later than the other two strains thus it may be the best choice for use for rangeimprovement or for irrigated pastures. However, it requires careful management because it is more susceptible to overuse than the other two strains. Switchgrass (Panicurn virgatum L.) is a perennial tallgrass adapted to the diverse climate and soils of the mid-continent and is widely distributed throughout the United States (Hitchcock) 1951). It is a productive warm-season forage-grass used primarily for summer grazing, and is most abundant on sandylands of the remaining natural grasslands of the Great Plains. Adapted strains and varieties are used in pure stands or in mixtures with other warm-season prairie grasses for range, pasture, and conservation plantings. In the Southern High Plains, yields of upland native rangeland were estimated to be from 730 to 1,120 kg/ ha on deep sand sites (Wilhite 1965), and from 2,240 to 2,575 kg/ ha on sandhill sites with more favorable plant-soil-water relations (Wilhite 1959). Most of these sites are now producing much less than their potential because of deteriorated range condition. Forage quality is an essential criterion in the selection and management of forage for livestock consumption. Phosphorus and protein are the most deficient components in livestock nutrition in the southwest. Crude protein in Texas range grasses decreases duringthe growing season and is not closely related to soil nitrogen content (Fudge and Fraps 1945). In Northwest Texas the phosphorus content of forage was sufficient for range cattle in 66% of the grasses early in the growing season but deficient in 91% of the grasses at maturity (Fudge and Fraps 1945). Average protein content of short and mid-grasses of the southern mixed prairie in Texas seldom meet the protein requirements of beef cows (Rogers and BOX 1967). Performance with limited moisture is of primary concern in evaluating and selecting superior forage plants. Water-use efficiency (forage production/unit of water) is of prime importance in Authors are soil scientist, U.S. Dep. Agr., Big Spri...

This study was conducted to determine the effects of three seedbed configurations, four mulch rates, and tractor traffic confinement on soil properties that affect soil‐water relations of a sandy soil with cotton as a test crop. The lack of water limits crop production on dryland sandy soils in the Southern High Plains.Undisturbed soil cores were taken from the 0‐ to 7.5‐, 7.5‐ to 15‐, and 22.5‐ to 30‐cm depths in the trafficked and nontrafficked interrows and crop rows of the flat, ridge, and furrow treatments. Surface mulch rates of 0, 5.6, 11.2, and 22.4 tons/ha of cotton‐bur mulch were applied annually after seedbed preparation to each split plot. Tractor traffic was confined to the same path each year using cotton (Gossypium hirsutum L.) as a test crop.Mulching at rates > 11.2 tons/ha reduced the bulk density, increased hydraulic conductivity, air porosity, total porosity, and organic matter content even in the trafficked interrows. Hydraulic conductivity of the crop rows increased eight‐fold with heavy mulch applications. Hydraulic conductivity increased three‐fold, bulk density was reduced, and air porosity increased as a result of controlling tractor traffic even without mulch.

To accurately interpret moisture readings taken by the neutron‐scattering technique in rocky soils, methods of access tube installation, influence of voids and rocks around access tubes, and accuracy of factory calibration curve were evaluated. Because access tubes could not be installed by the hand‐auger method where hard rocks were present, power‐driven portable drilling rigs were tried. Vacuum evacuation of cuttings in wet soils failed. Water injection worked well except in the presence of loose rocks. Air injection was most satisfactory except in wet clays. Voids around access tubes of < ⅜ inch had little or no influence on slow neutron count rates. Rocks had little influence on soil moisture determination unless they were large. Because readings of soil moisture from factory calibration seemed too high, a laboratory calibration curve was developed.

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Better management techniques and planting schemes are needed for the dryland agriculture of the Southern High Plains of the U.S. To test various possibilities cotton (Gossypium hirsutum L.) was grown on three seedbed configurations (flat, ridge, and furrow) with four mulch rates (0.0, 5.6, 11.2, and 22.4 tons/ha of cotton bur mulch). Soil water was measured to a depth of 300 cm by the neutron method. Preseason soil water storage (mid‐January to mid‐June) was highest for the 22.4 tons/ha mulch and least for no mulch. Precipitation storage efficiencies were 46, 68, and 80% from 34.0 cm of precipitation in 1968 and 36, 47, and 66% from 33.4 cm of precipitation in 1969 for the 0.0, 11.2, and 22.4 tons/ha mulch rates, respectively. The furrow plots had the highest accretion, and ridge plots, the least in 1968. During the 1969 season, accretion was highest in the furrow and similar in the flat and ridge plots. The 1968 soil water accretion and depletion showed the same relationship and similar quantities for the three mulch rates and seedbed configurations. Because of excessive precipitation at the end of the 1969 growing season, less depletion than accretion occurred from the two higher mulch rates. In 1967 cotton yields were similar in the 0.0 and 5.6 mulch subplots but were less than on the 11.2 and 22.4 tons/ha mulch subplots. In 1968 and 1969 yields were similar for the 11.2 and 22.4 subplots, but were significantly more than either the 0.0 or 5.6 tons/ha mulch subplots. More cotton was produced as a result of 5.6 tons/ha mulch than no mulch in 1968 and 1969 after two and three successive annual applications of mulch.