Brien E. Norton

Paddock Size and Stocking Density Affect Spatial Heterogeneity of Grazing

Abstract The claim that intensive rotational grazing (IRG) can sustain higher stocking rates can be partially explained by more even spatial distribution of grazing such that livestock consume forage from a greater proportion of a pasture. To test the hypothesis that utilization is more even at the higher stocking densities of smaller paddocks, mean absolute deviation (heterogeneity) of utilization estimates by plot was compared in paddocks of sizes and stocking densities representing increasing subdivision from two-paddock deferred rotation grazing (DRG) to 16-, 32-, and 64-paddock, two-cycle IRG. These 70-, 4-, 2-, and 1-ha paddocks were grazed for 7 wk, 4 d, 2 d, and 1 d, respectively, at 32 animal unit days (AUD)·ha−1 during 2000 and 34 AUD·ha−1 during 2001. Within IRG there was no response to the treatment gradient. After one cycle in the IRG paddocks, heterogeneity of use was generally lower than in the DRG paddocks, in both 2000 (3–11% [outlier 18%] vs. 14–19%) and 2001 (9–17% vs. 24–28%). After a second cycle in 2001, heterogeneity in half of the IRG paddocks (17–21%) was nearly as high as the early-grazed (24%), but not the late-grazed (28%), of the DRG paddocks. This lack of a stronger difference between systems was probably due to the fixed two-cycle IRG schedule and lack of plant growth during the nongrazing interval. Across both systems heterogeneity of utilization was strongly positively correlated with paddock size. Because utilization was not severely patchy in the largest treatment, the difference between systems would likely be greater in commercial-scale paddocks. Thus grazing distribution can be more even under intensive than extensive management, but this depends on how adaptively the system, particularly the aspects of timing and frequency, is managed.

An assessment of an indigenous soil classification used in the caatinga region of Ceara State, Northeast Brazil

Abstract An indigenous soil classification used in the caatinga region of Ceara State, Northeast Brazil, was mastered in the course of a resource inventory in the Acarau Valley. This paper considers its validity using (1) its usefulness as a tool for objectively grouping soils; and (2) the strength of the link between soil quality and class membership. Cluster analyses using morphological attributes from 36 profiles were used to determine how well the classification met the first criterion; percentage moisture equivalent and pH values were examined to assess the classification in terms of the second criterion. The classifications limitations and potential for wider geographic application were assessed in conjunction with a farm survey covering a larger portion of Ceara State. The cluster analyses produced three major clusters that corresponded closely to the broad classes of the indigenous soil classification. This corroborated the validity of the indigenous classification as a tool for objectively grouping morphologically similar soils. However, it was noticed that class names, although extensively used, may have different meanings in physiographically contrasting regions. Because of this it is necessary to establish the local relationship between class name and soil characteristics. Intra-cluster percentage moisture equivalent and pH values varied widely but tended to concentrate in relatively narrow areas of the range of values for all three clusters. This demonstrated the usefulness of the indigenous classification as a framework to group soils physicochemically.

Comparison of the reference unit method and dimensional analysis methods for two large shrubby species in the caatinga woodlands.

The reference unit technique was compared with the dimensional analysis approach for estimating large shrub foliige biomass in Northeast Brazil. The techniques were tested on coppicing jurema (Mhosa acutistipula Benth.) and pau branco (Auxemma oncocalyx [Fr. Alem.] Taub.). Both methods provided good estimates of foliage weight. The coeffkients of determination for the reference unit approach ranged from .890 to .985. The P values obtained in applying the dimensional analysis method were .937 and .948. Improvements in estimates with the reference unit method were obtained when (1) a branch unit of 19% of total plant foliage was used versus a unit of only 7%, (2) the branch unit resembled the appearance of the branching of the plant being estimated, and (3) estimations of 3 judges were averaged. Total foliage production on shrubs and trees is one of the most difficult parameters to measure or estimate on native rangelands. The woody material and variable growth form renders most traditional sampling methods, largely derived for agronomic conditions, impractical for shrubs. As a consequence, vegetation sampling technique manuals ha,ve made only passing reference to or given insignificant information on biomass estimation of shrub foliage or current growth (Brown 1954, NAS 1962, Newbold 1967, Pieper 1973, t’Mannetje 1978). Efficient estimations of browse availability are required for research on brush control and grazing animal diet studies. Shrub measurement techniques used in other semiarid areas of the world were examined with the prospect of adapting a suitable method for the caatinga species. The criteria for selection were that the method be nondestructive, time efficient, and relatively precise. Traditional ‘clip-and-weigh’ methods (e.g., Whittaker 1961) were eliminated from consideration because of the labor and cost required (Gimingham and Miller 1968, Rutherford 1979), and because the associated research design did not permit destructive sampling. The twig count method of Shafer (1963) and methods relating foliage weight to the dimensions of individual branches (Whittaker 1962, Ovington et al. 1963, Provenza and Urness 1981) were considered inappropriate because of the high density of coppicing branches sprouting from the stumps of the test species. Two sampling techniques were selected for testing on large shrubs of Northeast Brazil. The first of these employs the principle of matching standards against samples (Hutchinson et al. 1972, Andrew et al. 1979), such as estimating the number of multiples of the reference unit (e.g., leafy branch) present in the entire plant. This technique was tested by Andrew et al. (1981) on 2 small Australian shrubs (Atriplex vesicaria Heward ex Benth. and Maireana sedifolia F. Muell.) and compared favorably with other techniques for estimating shrub biomass. The second technique, dimensional analysis, requires establishing a relationship between Authors are research assistant and associate professor. Department of Range Science, Utah State Universitv. Logan 84322. This research was carried oiti as iart of the United States Agency for International Development Title X11 Small Ruminants Collaborative Research Support Program under Grant No. AID/ DSAN/ XWGaO49, in collaboration with the Empress Brasileira de Pesquisa Agropecuaria (EMBRAPA), Brazil. The support of the EMBAPA staff is gratefully acknowledged. The authors would also like to thank Joao Queiroz and Mireille Kirmse for help with data collection, Keith Owens and Alan Carpenter for manuscript review, and Drs. David Turner and Fred Provenza for advice on statistical analysis. Manuscript accepted January IO, 1985. JOURNAL OF RANGE MANAGEMENT 38(5), September 1985 easily obtained plant dimensions and foliage weight. A number of studies have shown that canopy volume is highly correlated with foliage weight (Cook 1960, Ludwig et al. 1975, Uresk et al. 1977, Lyon 1968, Kelley and Walker 1976, Bryant and Kothmann 1979, Guy 1981). Study Area and Methods The study area was located in Ceara State of Northeast Brazil (3.Y south latitude, 41° west longitude), much of which is dominated by semiarid tropical woodland, called the caatinga (Pfister et al. 1983). The test plants werejurema (Mimosa acutistipula Benth.) and pau branco (Auxemma oncocalyx [Fr. Alem.] Taub.), 2 common and widely distributed species. Morphological characteristics, habitat preferences and management values of these 2 species are described by Kirmse et al. (1983). Jurema is a thorny, small evergreen leguminous tree and pau branco is a deciduous tree; both readily coppice after being cut near ground level and develop a shrubby growth form. Fifteen coppicing jurema and pau branco plants were selected over a range of sizes. They graded in height from .45 to 2.00 m for jurema and .55 to 1.70 m for pau branco and represented the range of sizes available for goat browsing. The jurema plants had been cut 2 years previously; the pau branco plants were first year resprouts. The field data were collected in May, 1980, during the latter part of the rainy season. Reference Unit Technique The technique was tested by 3 observers (judges), 1 of which had 2 years previous experience sampling sagebrush (Artemisia tridentata Nutt.) biomass with the reference unit method. Prior to the beginning of the trial the experienced judge trained the inexperienced observers. This training involved estimating and verifying foliage biomass of 3 jurema shrubs of different sizes and was completed in 2 hours. Jurema The reference unit method was easily adapted to jurema because the growth form of a resprouted plant provided clearly distinguishable branches (Fig. 1). The procedure involved 3 steps: I) Representative branches, selected from plants not being tested, provided the reference units. The leafy growth on the branch comprised the reference unit per se. Andrew et al. (1979) suggested that the preferred size of the reference unit be IO-20% of the foliage weight of the average sample plant. Three branches (units) were used for jurema in this study. The smallest weighed 36 g (dry weight of foliage) and represented 7% of the average foliage weight of the 15 test plants. Two larger branches, each representing about 19% of the average plant, were also used for estimating jurema. Of these larger units, one had compacted branching and dense foliage typical of the test plants and the other had more dispersed foliage. For convenience, these 3 reference units will be referred to as small, large-compacted, and large-dispersed. 2) The number of times the foliage of the reference unit was replicated in the test plant was counted. Only the leaves were considered in the biomass estimations. The estimations were conducted in early morning in order to avoid any bias associated with wilting and curling of the leaves on these reference

The potential of Acacia albida for desertification control and increased productivity in Chad

Abstract Reforestation using Acacia albida has been preposed as a mechanismsfor combating desertification trends in the Sahel. This tree is characterised by a deciduous habit in the wet season; it is valuable for fodder, as a hardwood in woodwork industries, and for enhancing soil fertility of cropland. In a three-year project described in this paper, the establishment of Acacia albida platations in cultivated field in central Chad is conceived as a focal point to coordinate resource conservation and land development programmes. Several hundred thousand young trees were established and about 2500 farmers and their families participated in the revegetation programme. The success of the project must be evaluated, however, in terms of the prospects for long-term benefit and recognising the sociological problems of assistance programmes.

Influence of summer rainfall on root and shoot growth of a cold-winter desert shrub, Atriplex confertifolia

SummaryThe influence of irrigation and nitrogen fertilization in early summer on root and shoot growth of Atriplex confertifolia, a C4 shrub species, was examined in a cold-winter desert community in northern Utah. Soil water and xylem pressure potentials were monitored during the summer period.At the time of watering the surface soil (0–30 cm) was dry but there were turgid fine roots in this horizon. Watering of the soil reduced plant water stress from-30 to-15 bars (dawn values) indicating that roots near the surface were capable of absorbing water, and induced root growth in the 0–30 cm zone. The addition of N to the water treatment did not further increase root production. However, watering and watering +N fertilizer failed to stimulate shoot elongation or any dry weight increase of shoots. This shoot dormancy during summer is not typical of C4 plants and is probably associated with adaptation to the cool arid environment.

Grazing Management Can Improve Livestock Distribution: Increasing accessible forage and effective grazing capacity

On the Ground By managing for more even animal distribution, ranch managers can increase the amount of forage accessible to livestock and raise their effective grazing capacity. Smaller paddocks and higher stocking density improve the distribution of grazing in each paddock. A landscape of many, smaller paddocks will spread grazing pressure more evenly than one of fewer, larger paddocks.

The effects of subsurface irrigation on current and subsequent year's growth in shadscale.

Sursurface irrigation of individual A triplex confertifofiu (shadscale) plants was implemented in the field during the summer of 1976 through the use of vertical access tubes to a depth of 50 cm. Shoots were marked on control and watered plants and examined periodically by enumerating every leaf, bud, flower, fruit, and second-order stem. Plant response to subsurface irrigation as determined in the fall enumeration revealed a modest increase in stem length and leaf weight and summer production of lateral branches. The carryover effect of summer irrigation was reflected in new growth on shoots of watered plants in spring 1977 being more than twice the production of shoots on controls. The 1976 response to subsurface irrigation is thought to be carbohydrate storage and/or root development. Watering did not enhance bud or shoot survival overwinter.

PARTITIONING THE SOIL PROFILE TO MEASURE SHADSCALE RESPONSE TO WATER AT DIFFERENT DEPTHS

A technique was developed to partition the soil profile of plotted plants of Atriplex confertifolia so that soil water condition could be controlled at specific depths. During an experiment in August in a field environment, plant water status was more stressed when soil water availability was restricted to the top 10 centimeters of the profile compared to the deeper 30 to 40-centimeter zone. Soil water was more beneficial, however, when it was available throughout the profile.

Strategic Grazing Management for Complex Creative SystemsGrazing Management Can Improve Livestock Distribution: Increasing accessible forage and effective grazing capacity

On the Ground By managing for more even animal distribution, ranch managers can increase the amount of forage accessible to livestock and raise their effective grazing capacity. Smaller paddocks and higher stocking density improve the distribution of grazing in each paddock. A landscape of many, smaller paddocks will spread grazing pressure more evenly than one of fewer, larger paddocks.