Buffelgrass Pasture Research Articles

Segmentation of Landsat Thematic Mapper imagery improves buffelgrass (Pennisetum ciliare) pasture mapping in the Sonoran Desert of Mexico

The invasive exotic buffelgrass (Pennisetum ciliare) is a principal threat to the Sonoran Desert of southwestern North America. Buffelgrass is cultivated in cattle pastures throughout Mexico's northwestern state of Sonora, where it poses an invasion threat to surrounding desert lands. Automated remote sensing methods to detect buffelgrass pasture conversion at a regional scale have shown limited success, due in part to variable land-cover conditions, and in part to intrinsic heterogeneity in desertscrub land-cover. This paper discusses a novel technique for delineating and mapping buffelgrass pastures based on vector-based satellite image segmentation followed by pixel-based classification using ancillary spatial environmental data. Based on quantitative accuracy metrics and visual inspection of known pasture sites, we report that segmentation considerably improved the mapping process, in particular the detection and delineation of pastures. Comparisons of paired classifications with segmented and nonsegmented imagery revealed higher overall map accuracies and higher buffelgrass class accuracies, as well as lower errors of commission and omission for buffelgrass in segmented maps. This new application of object-based image analysis has promising implications for ongoing efforts to map and monitor buffelgrass expansion region-wide and other similar changes in land-cover type and condition across human-modified landscapes.

Effects of land conversion on the regeneration of Pachycereus pecten-aboriginum and its consequences on the population dynamics in northwestern Mexico

Pachycereus pecten-aboriginum is a columnar cactus currently threatened by the conversion of natural vegetation to buffelgrass pasture ( Pennisetum ciliare) in Sonora, Mexico. However, knowledge about its population dynamics is extremely poor, particularly in response to disturbance caused by pasture conversion. We set up experiments to evaluate seed removal, germination, seedling survival and compared demographic patterns on permanent plots from natural vegetation and pasture. Our experiments on regeneration show that seedlings were unable to establish in pasture because of high levels of mortality due to soil drying and cattle trampling. The population growth rate ( λ) was 1.060 and 1.086 for the 2006–2007 and 2007–2008 periods, respectively, in the native thornscrub vegetation. The slight increase in λ in 2007–2008 was a result of increased fecundity and seedling survival. The highest elasticity values correspond to the survival of large/old individuals. Using the average of both matrices, we obtained a mean matrix to perform numerical analyses simulating demographic variation to project the population behavior under buffelgrass pasture conditions. The numerical simulations suggest a decreasing population only when adult survival probabilities were affected. Given these limitations for population growth, our data suggest that adult populations that persist on pastures will be driven into local extinction.

Consequences of Buffelgrass Pasture Development for Primary Productivity, Perennial Plant Richness, and Vegetation Structure in the Drylands of Sonora, Mexico

In large parts of northern Mexico native plant communities are being converted to non-native buffelgrass (Pennisetum ciliare) pastures, and this conversion could fundamentally alter primary productivity and species richness. In Sonora, Mexico land conversion is occurring at a regional scale along a rainfall-driven gradient of primary productivity, across which native plant communities transition from desert scrub to thorn scrub. We used a paired sampling design to compare a satellite-derived index of primary productivity, richness of perennial plant species, and canopy-height profiles of native plant communities with buffelgrass pastures. We sampled species richness across a gradient of primary productivity in desert scrub and thorn scrub vegetation to examine the influence of site productivity on the outcomes of land conversion. We also examined the influence of pasture age on species richness of perennial plants. Index values of primary productivity were lower in buffelgrass pastures than in native vegetation, which suggests a reduction in primary productivity. Land conversion reduced species richness by approximately 50% at local and regional scales, reduced tree and shrub cover by 78%, and reduced canopy height. Land conversion disproportionately reduced shrub species richness, which reflects the common practice among Sonoran ranchers of conserving certain tree and cactus species. Site productivity did not affect the outcomes of land conversion. The age of a buffelgrass pasture was unrelated to species richness within the pasture, which suggests that passive recovery of species richness to preconversion levels is unlikely. Our findings demonstrate that land conversion can result in large losses of plant species richness at local and regional scales and in substantial changes to primary productivity and vegetation structure, which casts doubt on the feasibility of restoring native plant communities without active intervention on the part of land managers.

Urea levels in multiple supplement for lambs grazing on buffelgrass

The objective of present trial was to evaluate the intake of supplement dry matter, productive performance, carcass traits, and weight and yields of commercial meat cuts of lambs grazing on dormant buffelgrass pastures and receiving multiple supplementation containing different urea levels. Urea levels used were: 5, 8, 11 and 14% on dry matter. Thirty-six male lambs were used, nine animals per treatment, with 18.0 ± 2.0 kg initial body weight, distributed into four groups. The experimental design was completely randomized with nine replications. Urea levels in supplement did not influence productive performance, cold and hot carcass weight and yield and commercial meat cuts weight and yield (leg, shoulder, rib and brisket). Use of multiple supplements containing 11 and 14% of urea levels for lambs in dormant grazing pastures during the dry season may increase bioeconomic performance of this activity, as they promoted lower supplement intake and similar productive performance.

What Drives the Conversion of Native Rangeland to Buffelgrass (Pennisetum ciliare) Pasture in Mexico’s Sonoran Desert?: The Social Dimensions of a Biological Invasion

The introduction of invasive exotic plants has many social dimensions. Although a diverse literature identifies some of the social drivers of exotic plant introduction and subsequent invasion, relatively little attention has been given to the motives of individuals involved. This research focuses on the extensive conversion of native rangeland to exotic buffelgrass (Pennisetum ciliare) pasture by ranchers in Mexico’s Sonoran Desert using data gathered through systematic interviews and ordinary least squares regression modeling to demonstrate how a few social variables determine the extent of buffelgrass introductions. Results show that land allocation to pasture is determined chiefly by ranch size, with significant roles also played by rotational grazing, buffelgrass seed harvest, and exposure to government research. Results are contextualized and explored in depth, illustrating how the extent of rangeland-to-pasture conversion in this part of the Sonoran Desert is determined by direct and indirect social factors. The study also highlights implications for buffelgrass invasion.

Diet quality estimated with faecal near infrared reflectance spectroscopy and responses to N supplementation by cattle grazing buffel grass pastures

In the seasonally dry tropics the productivity of grazing cattle is often constrained by nutrition, particularly during the dry season. An experiment during 2 annual cycles estimated the diet selected by grazing Bos indicus heifers, and their growth and growth responses to a non-protein N supplement. Two drafts (groups) of 2 herds (10 heifers per herd) grazed a pasture consisting of buffel grass ( Cenchrus ciliaris) with some legume and edible browse, and herds were offered loose mineral mix (LMM) supplements either without (control) or with urea. Near infrared reflectance spectroscopy measurement of faeces (F.NIRS) was used to estimate each 2 weeks the non-grass and crude protein (CP) concentrations, and DM digestibility (DMD) of the diet selected. Rainfall and diet quality generally followed the seasonal pattern expected for the region and for the seasonally dry tropics. Non-grass ( i.e. dicotyledonous species) content averaged 0.13 (S.D. 0.053) of the diet and did not appear to be related to season, but during the first dry season and wet season the urea supplemented heifers selected diets lower ( P<0.01 and P<0.05, respectively) in non-grass than the control heifers. Diet quality was generally low during the dry seasons, increased sharply after the seasonal break, and later declined gradually through the wet seasons and wet-dry transition seasons. During the dry seasons average diet CP ranged from 33 to 49 g/kg and diet DMD from 0.480 to 0.507. During the 2 wet seasons CP averaged 94 and 100 g/kg, and the DMD 0.591 and 0.601. The control treatment heifers lost 30 and 32 kg LW during the late dry seasons, and gained 143 and 136 kg during the wet, wet-dry transition and early dry seasons of Drafts 1 and 2, respectively. F.NIRS predicted the daily weight gain (DWG) of the heifers with accuracy useful for management purposes except during the early wet season of Draft 2 when intermittent rains increased diet quality but were insufficient for substantial pasture growth. The urea supplement reduced ( P<0.01) heifer LW loss during the dry seasons, but much of this benefit subsequently disappeared due to compensatory growth; net benefit of the urea supplement over the annual cycle was 24 and 14 kg in the 2 drafts. This study demonstrated the capacity of F.NIRS to estimate the diet selected, liveweight change and liveweight responses to a N supplement in grazing cattle.

Soil carbon and nitrogen changes after clearing mulga ( Acacia aneura) vegetation in Queensland, Australia: Observations, simulations and scenario analysis

In the work reported here we examine the changes in soil (organic) carbon and nitrogen that are observed after converting a stand of nitrogen-fixing mulga trees ( Acacia aneura) to buffel-grass ( Cenchrus ciliaris) pasture that contained no nitrogen-fixing legumes. A range of previously reported field measurements was compared against the output of CenW 3.1, a reformulated version of the CENTURY model. The model successfully reproduced the observed patterns of soil carbon, C:N ratios and nitrogen mineralisation rates under mulga vegetation. This included relatively small changes in carbon concentration down to 1 m, C:N ratios of around 11–13 across all soil depths, substantial nitrogen mineralisation rates to a depth of 90 cm and, after clearing, an on-going decrease in soil organic carbon and nitrogen stocks. Interpretation of experimental observations was made difficult by the addition of a large amount of ‘dead’ organic matter from killed mulga roots after clearance. This material may be excluded through sieving (to 2 mm) in measurements taken shortly after tree removal, but may be included in later-year sampling as the partly decomposed material might be able to pass through sieves. Past work has usually ignored consideration of dead coarse roots. For the site carbon budget, changes in live biomass and surface litter significantly outweighed the small changes in soil organic carbon, and changes in decaying coarse roots were quantitatively more important than changes in other organic carbon pools. Modelled nitrogen mineralisation rates were lower under buffel-grass than those under mulga and showed significant year-to-year variations that were in line with varying rainfall. It showed no consistent trend over the first 20 years after clearing because the effect of decreasing nitrogen stocks was balanced by an increase in organic matter quality with the change from lignin-rich mulga litter to buffel-grass litter with lower lignin concentration. Nitrogen mineralisation rates gradually decreased thereafter as nitrogen stocks continued to decrease but litter quality stabilised. A scenario analysis showed that soil carbon and nitrogen trends could be affected by changing the nitrogen budget through inclusion of legumes or cessation of nutrient removal by grazing animals. Inclusion of legumes was needed to halt the decline in soil nitrogen and to ensure the long-term maintenance, or increase, in nitrogen stocks.

Influence of buffelgrass pasture conversion on the regeneration and reproduction of the columnar cactus, Pachycereus pecten-aboriginum, in northwestern Mexico

Buffelgrass ( Pennisetum ciliare) has been planted in large areas of desert and thornscrub of northwestern Mexico in order to increase forage production. However, no previous study has documented the influence of land conversion on the native species that persist on buffelgrass pastures. In this paper, we describe the influence of buffelgrass conversion on the regeneration and reproduction of the columnar cactus, Pachycereus pecten-aboriginum, in the state of Sonora. We selected three different pastures of different age and adjacent undisturbed thornscrub where we estimated abundance and population structure of this cactus. During the flowering season, we estimated several reproductive parameters. We also set up an experiment to explore whether seedlings are able to establish in the buffelgrass pasture. Our results indicate that land conversion has no significant effect on plant abundance, but a major effect on size distribution. For most reproductive parameters, no statistically significant differences were detected between thornscrub and pastures. Seedlings were able to establish only on thornscrub, as all seedlings that emerged in pasture died within 1 year. Land conversion has apparently a minor effect on plant reproduction, but a significant effect on the regeneration of this columnar cactus. Our data suggest that adult populations that persist on pastures are unable to self-replace and native populations will be driven into local extinction.

The Brigalow Catchment Study: III. Productivity changes on brigalow land cleared for long-term cropping and for grazing

Productivity of grain crops and grazed pastures inevitably declines without soil nutrient replacement and may eventually make these enterprises unprofitable. We monitored these declines in north-eastern Australia during 23 years after clearing 2 of 3 adjacent brigalow catchments, in order to define the productivity levels of developed brigalow land over time. One catchment (11.7 ha) was used for grain production and another (12.7 ha) for beef production from a sown buffel grass pasture. There was no upward or downward trend in annual rainfall amounts throughout the study period. In the cropped catchment, grain yield from 14 winter crops without added nutrients declined significantly in 20 years from 2.9 to 1.1 t/ha.year on the upper-slope clay soil (92 kg/ha.year) and from 2.4 to 0.6 t/ha.year on the Sodosol (88 kg/ha.year). Crop production per year declined by 20% between 2 successive 10-year periods. Wheat grain protein content also declined with time, falling below the critical value for adequate soil N supply (11.5%) 12 years after clearing on the Sodosol and 16 years after clearing on the clay soil. Such declines in grain quantity and quality without applied fertiliser reduce profitability. The initial pasture dry matter on offer of 8 t/ha had halved 3 years after clearing, and a decline in cattle liveweight gain of 4 kg/ha.year was observed over an 8-year period with constant stocking of 0.59 head/ha. Due to fluctuating stocking rate levels of 0.3–0.7 head/ha over the trial period, liveweight productivity trends are attributed to the multiple effects of stocking rate changes and fertility decline. The amount of nitrogen exported from the cleared catchments was 36.1 kg/ha.year in grain but only 1.6 kg/ha.year in cattle (as liveweight gain). Total soil N at 0–0.3 m declined by 84 kg/ha.year under cropping but there was no significant decline under grazing. The soil nutrients removed during grain and beef production need to be replaced in order to avert productivity decline post-clearing.

Faecal near infrared reflectance spectroscopy (F.NIRS) measurements of non-grass proportions in the diet of cattle grazing tropical rangelands

Frequent faecal near infrared reflectance spectroscopy (F.NIRS) analyses of faeces from cattle grazing a range of tropical pastures were used to measure the non-grass component, and other aspects, of their diets. Seasonal profiles of non-grass and crude protein in the diet are presented for nine sites from the speargrass, Aristida–Bothriochloa, and Mitchell grass dominated pasture regions, and for three shrubland sites where browse was plentiful. In grass-dominated native pastures of the speargrass and Aristida–Bothriochloa pasture regions of Queensland where little browse was available, non-grass was usually only 5–15% of the diet. Diet non-grass was even lower for a buffel grass pasture. In uncleared eucalypt woodland in the speargrass region, browse may have contributed up to 20% of the diet in the late dry season when grasses were senesced. In regions with abundant browse (e.g. mulga lands and desert upland systems) cattle preferentially selected actively growing grasses and forbs when they were available. With diminishing availability or declining quality of the forbs and grass due to grazing selection and dry conditions, browse increasingly contributed to intake. In Mitchell grass dominated pastures forbs often comprised more than 50% of the diet, and there appeared to be strong selection for forbs during the dry season. Where browse was available in association with Mitchell grass dominated pastures, it appeared to contribute to intake only in the late dry season. Dry season sampling in monsoonal tallgrass and Mitchell grass dominated pastures indicated dietary crude protein to be linearly correlated with diet non-grass, demonstrating the importance of non-grass in the prevention or alleviation of dry season protein deficiency in cattle. Changes in diet selected by cattle in relation to season and rainfall were generally in accord with the previous limited information, largely with sheep, in comparable vegetation systems. The results demonstrate the value of F.NIRS technology to assist understanding of diet selection by grazing cattle in northern Australia.

Impacts of land‐use change on nitrogen status and mineralization in the Mulga Lands of Southern Queensland

Abstract: In the semiarid Mulga Lands of southern Queensland soil nitrogen (N) levels have declined after clearance of the native mulga (Acacia aneura F. Muell. ex Benth.) and conversion to grazed buffel grass (Cenchrus ciliaris) pasture. At three mulga sites, declines in soil total N ranged from 14% to 28% in the surface 10 cm of soil. In situ net N mineralization from December 2003 until November 2004 in the surface 10 cm was 49.5 kg N ha−1 year−1 in the mulga woodland, 48.2 kg N ha−1 year−1 in the young (&lt;5 years old) buffel pasture (previously sown to wheat (Triticum aestivum L.) and 34.6 kg N ha−1 year−1 in the old buffel pasture (&gt;20 years). Ammonium‐N was the dominant N pool under mulga in the top 30 cm, while nitrate‐N was dominant under the buffel pastures. Although ammonium‐N under mulga was significantly different to that for 21‐year‐old buffel pasture at all depths, nitrification and net N mineralization were not different between the three land uses at any depth or in the entire 90 cm profile. The Soil Nitrogen Availability Predictor model was used to predict field N mineralization rates for the mulga woodland and 21‐year‐old buffel pasture by using a medium‐term (6‐week) laboratory incubation to establish basal rates of N mineralization. The Soil Nitrogen Availability Predictor overestimated annual net N mineralization in the 0–30 cm depth of mulga by 9% and underestimated it by 28% for the old buffel pasture. The Soil Nitrogen Availability Predictor could be modified further to accurately predict net N mineralization for the mulga woodlands.

Buffelgrass ( Pennisetum ciliare) land conversion and productivity in the plains of Sonora, Mexico

Bufflelgrass ( Pennisetum ciliare syn. Cenchrus ciliaris) is an African grass that has been widely introduced in subtropical arid regions of the world to improve rangelands for cattle production. However, it can have a negative effect on the diversity of native plant communities. Buffelgrass was introduced to Sonora, Mexico in the 1970s as a means to bolster the cattle industry. “Desmonte,” the process by which native desert vegetation is removed in preparation for buffelgrass seeding, alters the land surface such that buffelgrass plots are easily detectable from aerial and Landsat satellite images. We estimated the extent of conversion to buffelgrass in a 1,850,000 ha area centered on Hermosillo, from MSS and TM images from 1973, 1983, 1990 and 2000. We then compared the relative above-ground productivity of buffelgrass to native vegetation using Normalized Difference Vegetation Index values (NDVI) from Landsat and Moderate Resolution Imaging Spectrometer (MODIS) satellite sensor systems. Buffelgrass pastures have increased from just 7700 ha in 1973 to over 140,000 ha in 2000. Buffelgrass pastures now cover 8% of the land surface in the study area. Buffelgrass pastures have lower net primary productivity, estimated by MODIS NDVI values, than unconverted desert land. The desmonte process removes trees and shrubs, while the buffelgrass plantings are often sparse, leading to an apparent net loss in net primary production from land conversion. We recommend that the desmonte process be discontinued until its efficacy and safety for native ecosystems can be established, and that a comprehensive plan for preserving biodiversity while accomodating economic development be established for this region of the Sonoran Desert in Mexico.

Caracterização do pasto de capim-buffel diferido e da dieta de bovinos, durante o período seco no sertão de Pernambuco

Objetivou-se, neste experimento, quantificar a disponibilidade de massa seca e avaliar a composição botânica e bromatológica de pastagem de capim-buffel diferida e da dieta de bovinos, durante o período seco. Foram realizadas estimativas visuais para determinação da composição botânica e do corte de amostras, para determinação da disponibilidade da forragem, sendo os dados processados pelo programa BOTANAL. Três animais fistulados no esôfago foram utilizados para avaliar a qualidade e composição botânica da dieta selecionada. As médias foram comparadas pelo teste Tukey a 5% de probabilidade, empregando-se o procedimento estatístico SAS. Na pastagem foram encontradas 10 famílias, 19 gêneros e 19 espécies de plantas; os componentes que apresentaram maior disponibilidade e participação foram o buffel e a orelha-de-onça, variando de 1.392 a 2.750; e 1.167 a 1.215 kg de massa seca (MS)/ha, com participação de 50 e 30% na composição da pastagem, respectivamente. A composição bromatológica da pastagem variou de 63,0 a 81,6; 3,3 a 5,2; 0,9 a 1,4; 69,3 a 76,0; 53,0 a 57,4; 5,2 a 8,9; 86,0 a 88,6; e 10,8 a 16,4% para massa seca (MS), proteína bruta (PB), extrato etéreo (EE), fibras em detergente neutro (FDN) e ácido (FDA), material mineral (MM), carboidratos totais (CHOT) e não-fibrosos (CNF), respectivamente. A composição da extrusa variou de 18,5 a 22,3; 4,5 a 5,6; 1,3 a 1,9; 52,0 a 75,0; 52,3 a 59,8; 9,4 a 11,4; 81,8 a 84,4; 6,8 a 20,6; 45,7 a 49,1 para MS, PB,EE, FDN, FDA, MM, CHOT, CNF e digestibilidade in vitro da matéria seca (DIVMS), respectivamente.

El subsoleo como práctica de rehabilitación de praderas de zacate buffel en condición regular en la región central de Sonora, México

Ibarra FFA, Martin RMH, Ramirez MF. Tec Pecu Mex 2004,42(1):1-16. This study was conducted to evaluate the response of buffelgrass [Cenchrus ciliaris (L.) Link] and grama china (Cathestecum brevifolium Swallen) to the application of ripping as a compaction reduction practice to rehabilitate old buffelgrass stands in regular condition at central Sonora, Mexico. Ripping was conducted by triplicate on 400 m-2 plots in June of 1995 by using a three-blade ripper. The experimental design used was a randomized complete block with two treatments (ripping and no ripping) and three replications. Evaluated variables were: density, basal cover, height, forage production and soil compaction, and were monitored from 1995 to 1999. Ripping increased (P<0.05) buffelgrass and grama china density 83 to 383 %, basal cover 105 to 373 %, height 85 to 86 % and forage production by 113 to 338 % as compared to control, and reduced (P<0.05) surface soil compaction between 27 and 61 % on ripped plots during a 5-year period. Ripped plots produced a total of 9.81 t ha-1 of cumulative additional forage as compared to untreated control. It is concluded that soil compaction significantly limits productivity in old buffelgrass pastures.

The effects of finishing diet and postmortem ageing on the eating quality of the M. longissimus thoracis of electrically stimulated Brahman steer carcasses

Beef from cattle finished on grass will be of similar quality to that from cattle finished on grain when their carcasses are processed using best practice protocols. To test this hypothesis, carcasses of twenty Brahman steers, finished to 400 kg live weight on either Buffel grass pasture ( n=10) or grain ( n=10), were electrically stimulated with 400 V for 50 s 45 min postmortem, and their beef quality assessed 1 and 14 days postmortem. Hot weight, rump subcutaneous fat thickness and animal rate of growth in the 205 days preceding slaughter were recorded for each carcass as potential influences on beef quality. Quality of the M. longissimus thoracis (LT) at 1 and 14 days postmortem was evaluated using peak Warner–Bratzler shear force, compression, pH, cooking loss and taste panel acceptability, as well as by moisture and crude fat contents measured at 1 day postmortem. Results showed that steers finished on pasture grew the slowest and had the least subcutaneous fat at the same carcass weight. LT from carcasses of steers finished on pasture also had the shortest mean sarcomere lengths, suggesting these muscles may have been cold-affected, but there was no effect of diet on peak shear force. LT from carcasses of steers finished on pasture had the highest mean compression value, possibly because of increased collagen cross-linking associated with slow growth or increased exercise. Ageing significantly decreased LT peak shear force and compression values and increased cooking loss, L ∗ , a ∗ and b ∗ values. Taste panellists rated the aged, grass-finished beef the most tender and the best quality; however, the taste panel in this study may have favoured LT from grass-finished steers because it was significantly juicier than LT from the grain-finished steer carcasses. These results indicated that carcass composition and processing conditions interact to exert a greater effect on LT toughness and sensory acceptability than finishing diet. Ageing LT from steers finished on grass improved its colour, and thus may enhance its consumer acceptability.

Organic matter transformations and soil fertility in a treed pasture in semiarid NE Brazil

Planted silvo-pastoral systems are formed by sparing selected native trees when land is cleared for pasture establishment, or by planting selected species – often known agroforestry species – into the establishing pasture. Isolated trees within pastures and savannas are often associated with `resource islands', characterized by higher fertility and organic matter levels under the tree canopies. We here examine the processes underlying the differences in fertility and organic matter in a buffel grass (Cenchrus ciliaris L.) pasture that contained two tree species (Ziziphus joazeiro Mart., Spondias tuberosa Arruda Cam.) preserved from the native thorn forest and a planted agroforestry species (Prospois juliflora Swartz D.C). The objective is to distinguish effects of soil variability from those induced by the presence of trees or the planting of pasture. The δ13C signatures of the original (largely C3) vegetation, the preserved and planted trees, and the planted C4 grass were used to distinguish the provenance of organic matter in the top soil (0–15 cm). This allowed the conclusion that all trees maintained C3 derived C at the original thorn forest level, while lower levels under pasture were due to mineralisation of organic matter. The net rates of forest-derived C loss under pasture varied with soil type amounting to between 25 and 50% in 13 years after pasture establishment. Only on Alfisol, C inputs from the pasture compensated for the C3-C losses. Analysis of organic and inorganic P fractions indicated Z. joazeiro and P. juliflora enriched the soil under their canopy with P, whereas S. tuberosa had no positive effect on fertility. A combination of ANOVA and spatial analysis and mapping was used to show vegetation effects.

Bancos de proteína de leucena e de guandu para suplementação de ovinos mantidos em pastagens de capim-buffel

O experimento foi realizado com o objetivo de estudar, em ovinos mantidos em pastagens de capim-buffel, a utilização de leucena ou guandu, como bancos de proteína, durante estação seca. Foram testados nove tratamentos experimentais, constituídos pela combinação de três tipos de pastagens (capim-buffel, capim-buffel+guandu e capim-buffel+leucena), com três taxas de lotação (4, 6 e 10 borregos/ha). As pastagens, em duas repetições, foram estabelecidas em dezoito piquetes de 0,5 ha. Foram utilizados 60 borregos, com peso médio inicial de 19,4 kg, que receberam água e suplementação mineral completa à vontade e foram pesados a intervalos de 14 dias após 16 horas de jejum. Na pastagem de capim-buffel+leucena, foi possível elevar a lotação de quatro para seis borregos/ha, sem redução do ganho individual de peso dos animais, com conseqüente aumento da produção por unidade de área. Na pastagem de capim-buffel+guandu, não houve melhoria de desempenho dos animais em comparação à pastagem de capim-buffel. Concluiu-se que bancos de proteína de leucena podem melhorar a qualidade de pastagens de capim-buffel.

Control of Boophilus annulatus (Acari: Ixodidae) on cattle using injectable microspheres containing ivermectin.

The efficacy of an injectable microsphere formulation of ivermectin for control of the cattle tick, Boophilus annulatus (Say), was tested on 2 groups of 6 Hereford heifers held on separate 7-ha, tick-infested, buffel grass pastures. Cattle in one pasture were injected subcutaneously in the neck with a controlled-release microsphere formulation of ivermectin at the rate of 2.4 mg AI/kg body weight; the other group was injected with carrier only. Beginning 4 wk after injection and continuing throughout the remainder of the test (16 wk), no engorged ticks (> or = 5.5 mm) were found on any of the treated cattle, whereas large numbers of engorged ticks were found on the untreated controls. During this period, a few ticks were recovered from untreated sentinel animals placed in the treatment pasture during 7-8 wk after treatment, but none were recovered from animals exposed from 11-12 wk or 14-15 wk. Large numbers of B. annulatus ticks were found on untreated sentinel cattle placed in the control pasture during these same periods. Although the cattle, pastures, and tick habitat were approximately equal, the treated cattle gained an average of 77 kg compared with an average of 42 kg for the control group. This technology offers a possible alternative to the current official program of dipping and vacating pastures for eradication of Boophilus sp. infestations from the quarantine zone in southern Texas. Larger scale testing is needed to determine the potential of the injectable microsphere formulation and to optimize its use in eradication or control strategies.

REHABILITACION DE PRADERAS DE ZACATE BUFFEL INVADIDAS POR ARBUSTOS MEDIANTE EL USO DE LA QUEMA PRESCRITA

Ibarra FFA, Martin RMH, Miranda ZH. Tcc Peru Mex. 1999;37(3)9-22. Chirahui (Acacia cochliacantha H & B. ex Willd.) is an aggressive shrub which infests bnffelgrass [Cenchrus ciliaris (L.) Link] pastures and limits forage production in the arborescent brush type. This study was conducted in a bnffelgrass pasture highly infested with brush to evaluate the respoll.'e of the grass to brush control by prescriJJed burning. BlJrning was applied as a head-fire in June 1995 on three 50 ha plots. Evaluated variables were: total brush density, chirahui cover and buffelgrdss density, height, cover and forage production. Brush mortality witb fire was different (P<0.05) among species and varied from 25 a 81 %. Densities of chirahui were reduced by 58% with burning. Bnffelgrdss was not damaged by fire. Buffelgrdss forage production was 1.5 to 2.5 t ha-l greater (P<0.05) during all years on burned areas as compared to untreated controls. Burned pastures produced a total of 7. 7 t ha-l of cunlulative additional forage as compared to untreated plots. Although, prescribed burning controlled invasive shrub species, it also elinlinates important species for cattle and wildlife. Consequently, its application on buffelgrass pastures must be restricted only to sites with undesirdble brush species.

Soil Physicochemical Changes Following Buffelgrass Establishment in Mexico

Clearing brush from rangeland and seeding it to buffelgrass (Cenchrus ciliaris L.) is a popular range improvement practice in Mexico, but no data are available on the effects of these practices on soil properties. Twenty-nine study sites were randomly selected across 3 major climatic regions in Mexico: 13 in the northwest, 11 in the northeast, and 5 in the southeast. Soils under buffelgrass stands more than 10 years old and on adjacent virgin rangelands were sampled at 0-10, 10-20, and 20-30 cm depths to quantify sand, silt, clay, organic C, total N, pH, EC, CEC, available P, and exchangeable Ca2+, Mg2+, Na+, and K+.Because soil variables were not significantly (P 0.05) different among depths, only data from the surface horizon received further analysis. Soils in the northwest had higher (P 0.05) sand content and were particularly low in total N (0.08%), Ca2+, and K+, while soils of wetter and warmer southeast Mexico were significantly (P 0.05) higher than the other two regions in measures of soil fertility such as organic C (10 times higher), total N, and CEC (both at least 3 times higher). Long-term buffelgrass establishment had the most effect on soils in the southeast and no significant effect (P0.1) on soils of northeast Mexico. Soil organic C and total N both declined (P 0.025) by about 40% under buffelgrass pastures in the southeast; excgangeable Ca2+ decreased (P=0.027) by 21% in the same region, and Mg2+ declined (P=0.03) by 36% under buffelgrass in the northwest. Soil P did not respond to buffelgrass establishment. The findings of this study suggest that high forage yields following conversion of rangeland to buffelgrass pasture will be less sustainable in subtropical regions with high rainfall (mean of 1070 mm in this study) than in the semiarid zone with inherently poorer soils.