Experimental Ranch Research Articles

Biochar alters nitrogen and phosphorus dynamics in a western rangeland ecosystem

Application of biochar to soils has been proposed as a novel approach to managing wood residuals, enhancing soil carbon (C) storage and improving soil fertility; however, the majority of biochar studies have been conducted in agricultural systems that rely on tillage and nutrient inputs associated with annual cropping schemes. Few studies have evaluated the influence of biochar on soil processes in semi-natural rangeland ecosystems that feature more complex plant communities, lack deep soil disturbance, and have relatively few external nutrient inputs. In August 2018, biochar produced using wood waste from a lumber mill in Columbia Falls, MT, USA was applied to surface soils in replicated plots at an experimental ranch in western Montana to test the impact of biochar on soil C storage and nutrient management. A series of soil biochemical properties including total soil C and nitrogen (N), microbial N functional genes, available phosphorus (P) and the net accumulation of nutrients below surface soil layer were evaluated over a one-year period following biochar addition with or without a poultry litter based organic fertilizer. Biochar used alone slightly reduced soil NH 4 + , significantly increased soil nitrification potential, increased the relative abundance of the bacterial amoA gene, and increased the soil nitrate (NO 3 − ) pool size, while having no net effect on soil inorganic N accumulation below surface soil. By contrast, biochar charged with poultry litter (termed “charged biochar”) had no effect on NH 4 + availability, but had a positive effect on amoA abundance. Charged biochar significantly reduced NH 4 + accumulation below 25 cm depth compared to poultry litter alone. Biochar additions led to a shift towards a more fungal dominated community and a general increase in P availability. However, biochar alone also contributed to a greater amount of soluble P collected below surface soil, an effect slightly attenuated when biochar was applied with poultry litter. Soil pH increased from 5.7 to 6.9 in response to biochar addition and was one of the dominant factors governing the observed changes in soil processes. Charged biochar helped retain soil nutrients and promoted soil C storage in this semi-natural rangeland system over one growing season. Changes in these soil pools and fluxes may influence various trophic groups affecting ecosystem functioning over time. • Wood biochar used in a temperate rangeland ecosystem for nutrient management. • Relative abundances of bacterial amoA were significantly higher in biochar soils. • Biochar reduced soil inorganic N accumulation at depth over one season. • Biochar addition significantly increased surface soil biologically-based P. • Biochar used alone had positive effect on available P accumulation at depth.

Good practices in agricultural production for environmental conservation and “climate change mitigation” in the Ciénega region of the Jalisco State

The environmental crisis suffered by the planet is caused by multiple factors, such as the natural and anthropogenic. In agropecuary sector, some activities are developing that directly affect the natural resources. Motivated by that situation, this work was carried out with the objective of identifying and promoting the use of good practices in agricultural production for environmental conservation and “climate change mitigation” in the Ciénega region of the State of Jalisco. The work was carried out in an “Experimental Ranch” of the University of Guadalajara, located in the town of San José Casas Caidas in the Municipality of La Barca, Jalisco. The work included 23 agricultural producers from the municipalities of Ocotlán, La Barca and Jamay, from the Jalisco state. A participatory workshop was held as a methodological strategy, where different actors of the farming activity participated. As part of the results, the following problems were identified: lack of water, pests and diseases, hailstorms, presence of weeds, inefficient commercialization, as well as lack of financing. They propose to implement of soil conservation strategies such as; incorporation of crop residues, crop rotation, soil leveling, application of composts, among others.

Relaciones interespecíficas de forrajeo de gorrión de Worthen (Spizella wortheni) durante la época no reproductiva en Coahuila, México

El gorrión de Worthen (GW) (Spizella wortheni) en México es endémico de Coahuila, Nuevo León y San Luis Potosí, México. Actualmente, GW tiene una distribución restringida, se encuentra en poblaciones pequeñas y está en peligro de extinción. Esta especie se asocia a márgenes de colonias de perrito de las praderas y ha sido estudiada escasamente. Por ello, en la época no reproductiva (otoño-invierno), durante febrero y marzo, así como de septiembre a diciembre de 2015, bandadas mixtas asociadas al GW y monoespecíficas de GW fueron monitoreadas en el Rancho Experimental Los Ángeles, Coahuila, México. En este estudio, las especies asociadas al GW, su composición y tamaño de las bandadas fueron registradas; además, las características del hábitat de forrajeo fueron evaluadas. Trece especies de aves se asociaron al GW y tres tipos de asociaciones de alimentación del GW en bandadas fueron identificadas: 1) bandadas mixtas grandes, 2) bandadas mixtas pequeñas y 3) bandadas monoespecíficas de GW. El 57 % del número total de especies registradas en las bandadas tuvo hábitos alimenticios granívoros similares a los del GW. En las bandadas mixtas dominadas por G W, esta especie fue la líder o especie núcleo, mientras que en las bandadas dominadas por otra especie fue seguidora. Los componentes de hábitat asociados a las bandadas mixtas grandes fueron altura y cobertura de coyonoxtle (Cylindropuntia imbricata Haw.), mientras que los relacionados a las bandadas mixtas pequeñas fueron altura y cobertura de nopal rastrero (Opuntia rastrera Weber). La identificación de sitios no reproductivos de alimentación del GW en pastizales conservados puede representar una herramienta útil en el diseño de estrategias de conservación del GW y especies asociadas.

Genetic improvement for alpaca fibre production in the Peruvian Altiplano: the Pacomarca experience

SummaryPacomarca is an experimental ranch founded by the INCA group to act as a selection nucleus from which basic genetic improvement of alpaca fibre can spread throughout the rural communities in the Peruvian Altiplano. State-of-art techniques in animal science, such as performance recording or assisted reproduction including embryo transfer, are applied to demonstrate their usefulness in the Altiplano conditions. Pacomarca has developed useful software (Paco Pro) to carry out the integral processing of production and reproduction data. Mating is carried out individually, and gestation is diagnosed via ultrasound. Breeding values estimated from a modern genetic evaluation are used for selection, and embryo transfer is applied to increase the selection intensity. However, the objective of Pacomarca goes beyond, extending its advances to the small rural communities. Training courses for farmers are organised while searching for new ways of improving the performance of alpacas both technically and scientifically.

Evaluation of the upgraded spur model ( spur2.4)

Abstract spur (Simulation of Production and Utilization of Rangelands) is a grassland ecosystem simulation model. spur2.4 integrates all previous versions of spur . The changes from spur 91 make the model more applicable to the southern Great Plains. The forage submodel from spur 2 predicts forage intake and diet selection by grazing herbivores, and the cow-calf submodel from spur 2 simulates all individuals in a herd for their full life cycle, based on defined genetic traits. The soil organic matter submodel from century was added to improve soil carbon and nitrogen cycling. spur 2.4 output is compared with observed values from the Texas Experimental Ranch, Throckmorton, Texas. The changes made in creating spur 2.4 have considerably improved the utility and accuracy of the spur model for north Texas. Soil moisture predictions are improved ( spur 91 is 137% and spur 2.4 is 106% of observed, R =0.79–0.86), but run-off is still not adequate ( R =0.65–0.76) and monthly evaporation is lower ( spur 91 is 94% and spur 2.4 is 95%) than observed. Soil carbon level predictions by the century submodel are within range of the data, and output is stable over the simulation period. Predictions of individual plant species productivity compared with observed data are improved with spur 2.4 ( R =0.79–0.98). Between-season plant growth and long-term persistence are simulated well. The addition of the century soil organic matter submodel increased nitrogen level predictions resulting in more accurate predictions of animal weight gain. Steer weight gains are typical for north Texas. Simulation of cow-calf mass was good ( R >0.98) as was production per hectare and per cow. The addition of the cow-calf model increases the utility of the model. The paper identifies portions of the model that need further validation and field research to improve model utility and credibility for use in natural resource management.

Grazing pressure impacts on potential foraging competition between Angora goats and white-tailed deer

Abstract Increased Angora and Spanish goat populations in the Tamaulipan Province of southern Texas and northeast Mexico and the economic importance of white-tailed deer lease hunting in the region has heightened concern as to negative interactions between these two herbivores. This study selected a shallow ridge range site, dominated by palatable shrubs, as a high potential community for herbivore interaction at the landscape level. The site was stocked at 0, 2, 4, 6 goats/ha on an experimental ranch in South Texas. Deer and goat biting tactics, diet selection and reconstructed dietary crude protein and digestible organic matter were compared across stocking treatments. Dietary overlap indices were 0.75-0.88 between the herbivores across season and stocking rate. Deer had a greater tendency to use nip bites than goats in the non-grazed pastures (60–65% vs. 42–55%, respectively). However, goats increased the use of nip bites more than deer as intraspecific competition increased while deer used similar strategies across all stocking rates. Increased stocking rates had little impact on dietary composition of woody species in the diet of goats. The greatest dichotomies of dietary selection between both herbivores was shrubby bluesage where deer exhibited a positive preference while goats generally avoided the species, regardless of its availability. Both herbivores were generally able to stabilize nutrient concentration in their respective diets regardless of grazing pressure by goats.

Effects of skirting on yield, fineness, and value of wool from fine-wool range ewes.

Eighty-one mixed-age (2 to 8 yr old) Rambouillet ewes (58.5 kg, SD 5.9 kg) were randomly assigned to three treatment groups that contained similar numbers to study the effects of wool skirting on clean yield, fiber diameter, and prices received for fine wool. The sheep were managed as a single flock on an experimental ranch close to Barnhart, TX during the 4-yr study. Two fleece-skirting techniques (SK1 and SK2) were compared with a control procedure in which fleeces were not skirted before packaging (original bag, OB method). Skirted wools were higher yielding (P < .05) and contained less vegetable matter (P < .05) than skirts. However, clean yield and vegetable matter content of skirted and OB wools were not different (P > .05). Weight-averaged prices received for grease wool from the SK1, SK2, and OB treatments over the 4-yr period were 4.49, 4.36, and 3.83 $/kg, respectively. Prices received for both types of skirted wool plus skirts were higher (P < .05) than prices received for OB wool.

Nutrient Intake of Cattle on Rotational and Continuous Grazing Treatments

Many benefits have been obtained from rotational grazing, including management flexibility and livestock distribution, but long-term positive effects on plant and animal production have been inconsistent. The purpose of this cast study was to investigate nutrient intake of animals in 2 production scale grazing, treatments. The study site was the Texas Experimental Ranch located in Throckmorton County, in the eastern portion of the Rolling Plains of Texas. Treatments were a 465-ha, 16-paddock, 1-herd, cell designed rotational grazing system (RG) stocked at a heavy rate (3.7 ha . cow-1 . yr-1) and a 248-ha continuously grazed (CG) treatment stocked at a moderate rate (6.2 ha . cow-1 . yr-1). Size of RG paddocks was varied to create different livestock densities to simulate rotational grazing at a 14 and 42 paddock level. Comparisons were made to determine the effect of type of grazing system (RG vs. CG) and the effect of livestock density within the RG system on nutrient intake. Nutrient intake of esophageally fistulated steers was determined by daily dosing them with ytterbium nitrate-labeled forage and collection of fecal samples plus collection of fistula extrusa samples for crude protein and in vitro organic matter digestibility determinations. The only difference caused by different livestock densities was a higher (P < 0.001) intake of forage crude protein in the simulated 42 paddock system. Nutrient intake of steers in the CG treatment was greater (P < 0.001) than those in the RG treatment. Differences between treatment were attributed primarily to differences in stocking rate rather than grazing system.

Overstory-Understory Relations in Pinyon-Juniper Woodlands in New Mexico

Herbage biomass for blue grama (Boutdoua grdlis [H.B.K. Lag& pinyon ricegrass (Pfph&tu&un jimbriatum [H.B.K.] Hit&c.), New Mexico muhly (Muhihkgfa pcsrciflorcl Buckl.), other grasseq and forbs was estimated on 25 pinyon-juniper stands of varying overstory cover on the Fort Stanton Experimental Ranch insouthcentral New Mexico. Negative 2”d degree polynomial curvea best expressed the relationshipa between total understory and blue grama biomass and overstory canopy cover. Positive polynomial relationships were shown for cool-season graazs, New Mexico muhly, and pinyon ricegrass. Reducing pinyon-juniper canopy cover would likely increase blue grama production and reduce production of New Mexico mubly and pinyon ricegraas.

Seasonal Dynamics of Minerals in Forages at the Texas Experimental Ranch

Range livestock derive the bulk of their dietary mineral intake from forages that are often deficient in one or more essential minerals. The objective of this study was to quantify the seasonal dynamics of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations in the dominant native forages at the Texas Experimental Ranch. Concentrations were estimated by class of tissue (live and dead) for 5 species/ species groups: sideoats grama (Bouteloua curtipendula Michx.), Texas wintergrass (Stipa leucotricha Trin. and Rupr.), annual grasses, other warm-season grasses, and forbs. The study spanned a period of 2 years and included 16 sample dates. Although P, Mg, and K concentrations varied significantly among species and date, they varied primarily as a function of class of tissue. Averaged across dates and species, concentrations of P, Mg, and K in live tissue averaged 0.12, 0.13, and 2.02%, respectively, while concentrations in dead tissue averaged 0.04, 0.09, 0.57%, respectively. As a result, seasonal differences in whole plant concentrations of P, Mg, and K were closely linked to seasonal growth dynamics as they affect live/ dead ratios. Ca concentrations were affected more by species than class of tissue. Averaged across dates, Ca concentrations in live tissue averaged 0.55, 0.40, 0.42, 0.35, and 1.80%o in annual grasses, Texas wintergrass, sideoats grama, other warm-season grasses and forbs, respectively, while concentrations in dead tissue averaged 0.41, 0.40, 0.41, 0.36, and 0.96%, respectively. It is concluded that considerations must be given to the potential effect that a given treatment may have on plant growth dynamics to properly interpret its effect on whole plant concentrations of minerals.

14-vs. 42-Paddock Rotational Grazing: Forage Quality

Research was initiated at the Texas Experimental Ranch in 1981 to quantify the effects of 2 livestock densities on forage quality in a rotational grazing (RG) treatment. Livestock densities evaluated were equivalent to 14 and 42-paddock RG treatments. Baseline data were collected in 1981 from 3 adjacent 30-ha paddocks in a 465-ha, 14-paddock, cell designed RG treatment stocked at a rate of 3.6 ha/cow/year. Near the beginning of the 1982 growing season the center paddock was subdivided into three, 10-ha paddocks to establish the RG-42 treatment. Herbage standing crop was harvested before and after each grazing event during the 40-month period, separated by species or species group into live and dead tissue, and each fraction analyzed for percentage crude protein (CP) and organic matter digestibility (OMD). Livestock density had minimial effect on forage quality. Live tissue was of higher quality than senesced tissue regardless of plant species. Increases and decreases in overall quality during grazing periods were positively associated with rates of plant growth. Number of periods when forage quality increased or decreased during grazing and magnitude of change were unaffected by treatment. Lack of significant treatment effects on forage quality is attributed to the general absence of significant treatment effects on forage production, species composition, and live/dead ratios.

14- vs. 42-Paddock Rotational Grazing: Aboveground Biomass Dynamics, Forage Production, and Harvest Efficiency

Research was initiated at the Texas Experimental Ranch in 1981 to quantify the effects of 2 stocking densities, equivalent to 14 and 42-paddock rotational grazing (RG) treatments, on aboveground biomass dynamics, aboveground net primary production (ANPP), and harvest efficiency of forage. Baseline data were collected in 1981 from 3 adjacent 30-ha paddocks in a lepaddock, cell designed RG treatment. Near the beginning of the 1982 growing season the center paddock was subdivided into three, lo-ha paddocks to establish the RG-42 treatment. Stocking densities in the 14 and 4Zpaddock treatments were 4.2 and 12.5 AU/ha, respectively, from March 1982 to June 1984 and 3.0 and 9.1 AU/ha from June to November 1984. During 1981, estimated ANPP in the two RG-14 paddocks averaged 4,088 kg/ha as compared to 5,762 in the single RG-42 paddock. Following subdivision, ANPP in the RG14 paddocks averaged 2,533 kg/ha as compared to 2,670 kg/ha in the RG-42 paddocks. Although ANPP varied significantly among the 4 years of the study it was not affected by density treatment. Likewise, harvest efficiency varied among years but was unaffected by density treatment. Average harvest efficiency over the 4 years was about 42%. Aboveground biomass dynamics were also generally unaffected by density treatments.

Short Duration Grazing in Central New Mexico: Effects on Infiltration Rates

The objectives of this study were to determine the infiucnce of short duration grazing, continuous grazing, and grazing exclusion on infiltration rates on 2 range sites in southcentral and eastcentral New Mexico. Short duration grazing had no beneficial effect on the hydrology of 2 different range sites. The terminal infiltration rates of both short duration grazing systems, after the cattle had grazed the area, were about one-half the terminal infiltration rate of the same area before the cattle grazed the area. Cattle distribution within the different grazing treatments had no effect on infiltration rates at 0.4,0.8, and 1.2 km away from water for a moderate continuous, heavy continuous, and a short duration grazing system. Moderate continuous grazing was superior to heavy continuous grazing and short duration grazing, based on the hydrologic variables evaluated. Grazing systems impact range watersheds by altering vegetation and soil variables. The objectives of most grazing systems are to increase forage production while, at the same time, increasing livestock and wildlife production. In the past several years, researchers have studied several different grazing systems and their effect on surface water runoff and sediment production. However, little is known about the effect of short duration grazing on rangeland watersheds. A short duration grazing system is defined here as having a stocking density index greater than 2 (Kothmann 1974), but is distinguished from a high intensity, low frequency grazing system by grazing periods of less than 2 weeks. Aldon and Garcia (1973) studied the effects of changing from heavy continuous to moderate continuous grazing with summer deferment on a 190-ha watershed. They reported sediment yields decreased 71% over a 4-year period. Smith (1980), working at the Ft. Stanton Experimental Ranch in southcentral New Mexico, noted moderate continuous grazing was superior to either heavy continuous grazing or a Cpasture l-herd rotation grazing system. Smith (1980) concluded that reduced vegetal cover on the heavy continuous and 4-pasture l-herd systems was the predominate reason for decreased infiltration rates and increased sediment production. Wood and Blackburn (198 I), in the Rolling Plains of Texas, reported a 4-pasture 3-herd grazing system (Merrill system) approached the optimum infiltration rate of a 20-year old exclosure. On the basis of analyzing infiltration rates, Wood and Blackburn concluded the deferred-rotation system was superior to moderate continuous; high intensity, low frequency (HILF); or heavy continuous grazing. McGinty et al. (1979), working in Sonora, Texas, reported infiltration rates of midgrass interspace areas were highest in a livestock exclosure and a deferred-rotation pasture. The heavy continuous grazing treatment significantly reduced terminal infiltration rates. McCalla et al. (1984) initiated another study at the Sonora Research Station to evaluate the influence of mixed livestock grazing on the hydrologic variables in moderate continuous; heavy continuous; and a high-intensity, low frequency grazing system stocked at a moderate level. The pastures were 5 ha each and were grazed at a ratio of approximately 50:25:25% for cattle, goats, and sheep, respectively. In general, he concluded there was no signifi

Cattle Grazing Blue Grama Rangeland I. Seasonal Diets and Rumen Fermentation

Cattle Grazing Blue Grama Rangeland I. Seasonal Diets and Rumen Fermentation

Performance and Phosphorus Status of Range Cows with and without Phosphorus Supplementation

Performance and Phosphorus Status of Range Cows with and without Phosphorus Supplementation

Diurnal Variation in Weight and Rates of Shrink of Range Cows and Calves

Cow-calf pairs were weighed on successive mornings to determine the effects of time on total weight. Early morning weights of mature Hereford/Angus crossbred cows were approximately 2.5% less than late morning weights in both the spring and summer. Weights of suckling calves were not signifilcantly different between early and late morning. Linear regression analyses indicated drylot shrink weights of cows were pnmarily a function of length of time of shrink. Rate of weight loss was approximately 1% every 3 hours after an initial 3 hour loss of 3.5%. Secondary factors were status of cow (dry or wet), relative humidity (%), season (spring or summer) and initial cow weight. Shrink rates were slightly greater for wet cows than dry cows; when relative humidity was low; during spring; and for lighter weight cows. Rates of shrink of calves were primarily related to size of calf with calves weighing less than 53 kg (117 lb) gaining weight and calves weighing more than 53 kg losing weight. Differences in liveweight of livestock are often used to evaluate the effect of various experimental treatments on livestock performance. At the Texas Experimental Ranch the magnitude of weight change over time of individual cows and the weaning weight of their calves are the principal parameters utilized to contrast the effects of stocking rate, grazing system and level of winter supplement (Heitschmidt et al. 1982). Because of the number of cattle in each treatment herd, gathering and weighing generally begins in early morning and extends into the early afternoon over a period of 3 days. Thus, weight differences between herds may reflect not only treatment effects but also the effects of the time of day the animals were gathered and weighed. The first objective of this study was to quantify differences in cow and calf weights as a function of time of day when weighed. The second objective was to examine the rate of drylot shrink of both cows and calves as a function of length of shrink, envi ronmental conditions, initial weight and time of day when the animals were gathered and penned. This objective was established to evaluate the feasibility of gathering herds and weighing after a predetermined period of shrink so as to standardize weights.

The Impact of Grazing Systems on the Magnitude and Stability of Ranch Income in the Rolling Plains of Texas

Results of a 1961-1974 grazing system study on the Texas Experimental Ranch in the Rolling Plains were used to evaluate annual net income stability characteristics for a cow-calf opera- tion. A linear programming risk analysis model was utilized to select optimal combinations of grazing systems which minimized annual negative net income fluctuations. Greatest annual net incomes, expressed in 1979 dollars, were obtained from heavier stocked, continuously grazed systems which received winter feed. For the 1961-1974 period, annual net income stability was not increased by selecting combination of grazing systems. However, when only the last 5 years were included in the analysis, the stability of annual net income was improved by selecting a combination of grazing systems. Supplemental winter feeding did not have a signif- icant effect on annual net incomes. However, under heavier stock- ing rates the standard deviation of annual net income was approximately doubled when cows did not receive supplemental winter feed. Annual income and income variability was determined to have increased during the last 5 years of the study, relative to the total study period. It is hypothesized that a portion of this increased variability at the heavier rates of stocking is the result of changes in the composition of vegetation. The general increase in variability across all systems indicates that ranch operators may need to consider alternatives for risk management as well as man- agement for profits. Ranch operators have long strived to become more efficient in the management of their ranch resources. This effort has been made in order to increase economic returns and reduce economic risks associated with ranching. Risks in the ranching industry are as a result of the nature of livestock market, weather, diseases, prices paid for inputs, the use of credit, and government regulation. In the Rolling Plains of Texas, and in the Great Plains in general, the need to reduce adverse economic impacts of fluctuating forage supplies has resulted in considerable research efforts by public institutions and agencies. A major goal of range research is to identify alternatives to more efficient harvest forage from range- land and to increase forage quantity and quality for use by domes- tic livestock. The major purpose of this study was to evaluate net returns and the annual stability of these net returns from five grazing management systems in the Rolling Plains of Texas from 1961 to 1974 (Fig. 1). In developing a ranch management plan, it is assumed that net income levels and net income stability (risk) associated with var- ious production strategies for increasing net income are of concern to ranch operators (Markowitz 1959). Agricultural firm managers

Short Duration Grazing at the Texas Experimental Ranch: Weight Gains of Growing Heifers

Short Duration Grazing at the Texas Experimental Ranch: Weight Gains of Growing Heifers

Short Duration Grazing at the Texas Experimental Ranch: Effects on Aboveground Net Primary Production and Seasonal Growth Dynamics

The effects of short duration grazing on aboveground net primary productivity (ANPP) and seasonal growth dynamics were evaluated. Total ANPP was estimated to be 234 g/m2 in 1978 in the ungrazed control plot as compared to 330 g/m2 in the grazed treatment plot. ANPP estimates in 1979 were 352 and 268 g/m2 in the ungrazed and grazed treatments, respectively. Close examination of growth dynamics suggest that under certain environmental conditions grazing accelerated vegetative growth. The effect of livestock grazing on rangeland vegetation has been most often related to changes in standing crop resulting from changes in species composition (Sims et al. 1978, Sims and Singh 1978, Van Poollen and Lacey 1979). But information regarding the effects of grazing on the dynamics of aboveground net primary production (ANPP) are seriously lacking. A primary reason for the lack of such studies can be related to experimental design. With year-long and seasonal grazing systems, fenced exclosures or portable cages must be utilized to prevent livestock consumption of forage. Exclusion of livestock grazing creates an artificial environment because periodic grazing may alter the growth response of a plant in contrast to a non-grazed plant (McNaughton 1979). This problem may in part be alleviated in a short duration grazing system (SDG) if the period of grazing is short. Utilizing frequent harvest techniques, the effects of grazing on the dynamics of aboveground growth may be evaluated and estimates of ANPP calculated. The primary objective of this study was to quantify the shortterm effects of a SDG system on aboveground biomass dynamics and ANPP. It has been hypothesized that an increase in AN PP will occur at optimal levels of herbivory (Dyer 1975, McNaughton 1979) and Heitschmidt et al. (1982a) hypothesized that an increase in ANPP may be a major factor whereby a significant increase in livestock carrying capacity may be realized following implementation of a SDG system utilizing the method of grazing advocated by Savory (1978). Treatment and Study Area The study was conducted at the Texas Experimental Ranch located (994 14'W, 330 20'N) in Throckmorton County during the 1978 and 1979 growing seasons. The ranch consists of approximately 2900 ha of native grasslands. Continuous weather data since 1961 (unpublished), indicates a highly variable climate of warm wet springs and falls, mild winters, and hot summers. Mean daily maximum temperatures range from 13? C in January to 360 C Authors are associate professor and former research associates, Department of Range Science, Texas A&M University Research and Extension Center, Box 1658, Vernon 76384. Appreciation is expressed to the Swen R. Swenson Cattle Company for providing the land, livestock, and facilities for this research project. Report is published with approval of the Director, Texas Agricultural Experiment Station as TA 16357. in July. Mean daily minimum temperatures range from -3?C to 21?C in January and July, respectively. Average precipitation is 690 mm bimodally distributed (Fig. 1). Average frost-free growing season is 233 days extending from March to November. Study plots were located in an ungrazed area and in one pasture of a 10-pasture SDG treatment. The SDG treatment was stocked with Hereford/Angus crossbred growing heifers. Because of an inadequate labor force during winter months, the trial was run only from early April to early October each year. Stocking rate during these 6 months was 0.24 ha/AUM. A stocking rate near 0.54 ha/ AU M is considered moderate for mature cows under yearlong continuous grazing at the ranch (Heitschmidt et al. 1982b). Length of each grazing event ranged from a minimum of 3 days during periods of rapid vegetative growth to a maximum of 7 days during summer dormancy. Periods of rest ranged from 35 to 42 days. Both treatment plots were 60 X 60 m subdivided into two 30 X 60 m replicates. Slope was approximately 1% with a southwest exposure. The ungrazed plot was located approximately 30 m south of the grazed plot. Prior to initiating the study in 1978, both areas were periodically grazed at a moderate rate of stocking during various grazing trials. The ungrazed treatment plots had not been grazed for approximately I year. The grazed plots had not been grazed for approximately six months.

Cow-Calf Response to Stocking Rates, Grazing Systems, and Winter Supplementation at the Texas Experimental Ranch

Cow-calf performance from 1960 through 1978 was contrasted between three grazing treatments at the Texas Experimental Ranch. Grazing treatments were yearlong continuous stocked at annual rates averaging 5.1 and 7.6 ha/ cow and a 4-pasture, 3-herd deferred rotation system stocked at an annual rate averaging 7.2 ha/cow. Averaged across three weighing periods, cows in the deferred rotation treatment averaged 447 kg while weight of cows in the heavily and moderately stocked continuous treatmentsaveraged 427 and 438 kg, respectively. Calf weaning weights averaged 204,212, and 217 kg for the heavy continuous, moderate continuous, and Merrill rotation treatments, respectively. Production/cow averaged 182,189, and 202 kg while production/ha averaged 35.9, 25.2, and 27.8 kg, respectively, for the heavy continuous, moderate continuous, and deferred rotation treatments. Cows fed winter supplement were significantly heavier in early spring and summer than nonsupplemented cows with no sign&ant differences in weights by late summer. Supplemented cows weaned calves averaging 214 kg as compared to 208 kg for calves weaned from nonsupplemented cows. Winter supplementation significantly increased production in the heavily stocked treatment but not in either of the moderately stocked treatments. Numerous statistically significant interactions accompanied the significant main effects, and the biological significance of each was examined. The Texas Experimental Ranch was created in 19S9 to provide researchers with the necessary facilities to evaluate the longterm responses of both livestock and vegetation to various grazing systems and rates of stocking. Kothmann et al. (1970, 1971) concluded from a thorough analysis of the cow-calf performance data collected at the ranch from 1961 through 1968 that no economic advantages were apparent from either yearlong continuous grazing at a light rate of stocking (I 1.5 ha/ AU) or from a 2-pasture, l-herd deferred rotation system (Joubert 1958) stocked at a moderate rate (8.4 ha/ AU) when contrasted to continuous grazing and a 4-pasture, 3-herd deferred rotation system (Merrill 1954) stocked at a moderate rate (8.0 ha/AU). In addition, it was concluded that feeding cottonseed meal (41% CP) as a winter supplement at a rate exceeding 0.68 kg/day was not economically justifiable in any of the grazing treatments. Thus, in 1969 only three grazing treatments that had been initiated in 1960 were continued. These treatments were yearlong continuous grazing at moderate and heavy rates of stocking and the 4-pasture, 3-herd deferred rotation system.