Rhodes Grass Pastures Research Articles

Carbon sequestration under subtropical perennial pastures I: Overall trends

The use of subtropical perennial grasses in temperate grazing systems is increasingly being promoted for production and environmental benefits. This study employed a combination of elemental and stable isotope analyses to explore whether pastures sown to either kikuyu (Pennisetum clandestinum) or a combination of panic (Panicum maximum) and Rhodes grass (Chloris gayana) could increase soil organic carbon (SOC) levels in five regions across southern Australia. Carbon was sequestered under kikuyu at a rate of 0.90 ± 0.25 Mg C ha–1 year–1 along the south coast of Western Australia. Lower but still significant sequestration rates were found for kikuyu in South Australia (0.26 ± 0.13 Mg C ha–1 year–1). No changes in SOC were found for panic–Rhodes grass pasture systems in the northern district of Western Australia. Additionally, we found no changes in SOC when kikuyu-based pastures were established on formerly cropped paddocks in the Namoi Catchment of New South Wales. Stable isotope results corroborated these findings and suggested that, where SOC has accumulated, the gains have been dominated by SOC derived from the perennial vegetation and have been concentrated in the upper 10 cm of soil.

The effect of seeding rate and weed control on the establishment of Rhodes grass in the Eastern Cape

Abstract The effect of four seeding rates (3; 6; 12 and 24 kg/ha), four methods of weed control (nil, mowing, 4 l/ha of 2,4‐D amine and hand weeding) and two times of cutting (late boot stage and end of season) on the establishment and yield of a Rhodes grass pasture was investigated. The experiment was first sown in 1980 and repeated in the same form in 1982. Mother and daughter plants were counted and the canopy cover of Rhodes grass was estimated a year after seeding. Subsequently, the experiments were harvested a number of times. Seeding rate, weed control and cutting affected the density of plants. The higher densities affected the yield of the pasture initially only. The value of using more than 3 kg/ha of commercial certified seed is doubtful. The use of adequate measures to control weeds does seem to be economically justified.

Simulation of small systems using microcomputers

This paper focuses on models of small or partial systems, which generally tend to be less complex than the usual type of models. Microcomputers provide an ideal vehicle for these exercises, and the capabilities, advantages and limitations of these are discussed. Philisophical advantages of this approach are given. These are illustrated by descriptions of a number of modelling exercises conducted recently by the author, including seed production in Rhodes grass pastures, plant dynamics in Mitchell grass pastures, and post-harvest management of horticultural produce.

Soil treatment, plant species and management effects on improved pastures on a solodic soil in the semi-arid subtropics. I. Dry matter and botanical composition

Pastures of Rhodes grass (Chloris gayana), temperate legumes (annual medics) and a tropical legume (siratro) were established on a solodic soil in 1973-74 at Kogan in the semi-arid subtropics of southern Queensland. The effect of soil treatments, sown pasture species and cattle stocking rates on dry matter yields and botanical composition were measured during 1974-79. Nitrogen deficiency was a key factor limiting herbage production. Increased nitrogen in the ecosystem applied as fertilizer increased mean presentation dry matter of Rhodes grass pastures from 990 to 3443 kg/ha. Use of hydrated lime and gypsum (HLG) and annual medics with Rhodes grass increased dry matter yields from 990 to 1773 kg/ha. Where HLG had been applied, the annual medics re-established from seed each autumn and early winter throughout the period studied. Siratro established well at sowing and contributed initially to herbage production but then declined to almost zero. Deep subsoiling had no significant effect on dry matter yields or siratro persistence. Applied phosphorus at 48 kg Plha at establishment significantly increased herbage yields of Rhodes grass compared with 24 kg P/ha but no significant effects at either rate were found with a further 60 kg P/ha applied as 12 kg P/ha.year. Rhodes grass, which is tolerant of high soil sodium and magnesium status, maintained frequencies above 90% in treatments where the levels of nitrogen and phosphorus were high and when grazed at 0.62 steers/ha. However, deterioration occurred where nitrogen and phosphorus were lower or grazing pressure was higher, resulting in an ingress of native grasses. Twenty-five volunteer grass species were identified, the main genera being Eragrostis and Chloris. The need for a self-regenerating annual summer-growing legume in this environment is discussed.

Uptake by grass and transfer to soil of nitrogen from 15N-labelled legume materials applied to a Rhodes grass pasture

Unground legume materials labelled with 15N were applied to the soil surface under a Rhodes grass pasture in south-eastern Queensland and the recovery of the applied 15N was followed over periods of 1-3 years. Comparisons were made between two legumes, Macroptiliurn atropurpureurn cv. Siratro and Desrnodiurn intorturn cv. Greenleaf, between leaf and stem materials of different nitrogen (N) concentrations (0.5-3.8% N), and between fresh and dried materials. After 1 year, 15N in the applied materials had decreased by 25-91%, and 7-25% was recovered in the Rhodes grass. Except for leaf material of Greenleaf, these changes showed a positive, non-linear relationship to the percentage of N (%N) in the applied materials. The changes for leaves of Greenleaf were less than would be predicted from their %N. Drying Siratro leaves and stems before applying them to the soil surface did not significantly affect the above changes. For N-poor materials (0.5-1.8% N) applied at 380-1360 g dry matter m-2, uptake of 15N by Rhodes grass was greater in the second year than in the first year, whereas for N-rich materials (3.8%N) applied at 140 g dry matter m-2 uptake of 15N in the second and third years was only 23 and 12% respectively of that in the first year.

Dry matter, protein, energy and fibre intake by dairy heifers grazing a Rhodes grass (Chloris gayana) pasture

Dry matter (DM), protein, energy and fibre (ADF) intakes of Friesian and Ayrshire dairy heifers grazing a Rhodes grass pasture in Central Kenya were studied by indicator techniques for ten 22-day periods, each comprising 10 preliminary days and 12 collection days. Digestibility coefficients of DM, CP, GE and fibre were higher ( P < 0.05) in the wetter periods and generally declined during the drier periods, as pasture matured. Intakes of DM, DCP and DE decreased ( P < 0.05) as herbage matured. Average daily intake per kgW 0.75 was 73.9-g DM, 4.1-g DCP, 31.8-g ADF and 167-kcal DE. Average daily gain (ADG) also varied ( P < 0.05) with period and was positively related to intake of digestible dry matter, protein and energy. When conditions were wet, ADG was satisfactory at 480 g. In dry conditions, the heifers ingested 26.1-g DDM, 1.6-g DCP and 110-Kcal DE per kgW 0.75 daily and gained at 200 g/day, and supplementation was deemed necessary to sustain an optimum ADG of 550 g. The factors which may have limited pasture intake by the grazing heifers are discussed. In general, a Chloris gayana pasture, grazed at an appropriate stocking-rate, will meet the requirements of dairy heifers for maintenance and, to a variable degree, those for growth in areas of Kenya with an annual rainfall of 1400 mm and with a high potential for increased cattle production.

Intensive fattening of beef cattle on Rhodes grass pastures on the Lilongwe Plain, Malawi.

Beef fattening experiments were conducted in two wet seasons with Malawi zebu (Mz) and Friesian X Malawi zebu (F X Mz) steers grazing nitrogen-fertilised Rhodes grass pastures. The effects of stocking rate (5,7-5 or 10 steers/ha) and level of supplement (maize: madeya (maize bran) fed to steers at either 0-6 or 1-5 per cent of liveweight) were investigated over a 100 day period. Neither stocking rate nor supplement had an effect on daily liveweight gain but gain per hectare increased significantly with stocking rate. Comparative performance of the two breed types showed that the superior absolute gains of the F X Mz steers were not reflected in the efficiency parameters of supplement conversion or gain and carcass yield per unit liveweight. Hindquarter percentage was higher and subcutaneous fat was better distributed in the F X Mz. The practical significance of the results is discussed.

Pathways for losses of fertilizer nitrogen from a Rhodes grass pasture in south-eastern Queensland

The importance of surface run-off water, leaching and evolution of gases on losses of nitrogen fertilizer from a Rhodes grass pasture in south-eastern Queensland were assessed. Field microplots encased in steel tubes 21 cm in diameter and 60 cm deep were equipped to collect surface run-off, fertilized with 15NH415NO3 prills at the rate of 150 kg nitrogen ha-1 and destructively sampled at 4, 8, 12, 16 and 40 weeks after fertilizing. The recovery of 15N in the soil-plant system, losses of 15N in surface run-off and movements of 15N down the soil profile were measured. Open pasture plots were fertilized with NH4NO3 at rates of 0 and 150 kg nitrogen ha-1 and harvested at the same times as the microplots. The results were used to calculate the apparent recovery of fertilizer nitrogen by the plant tops. Pasture cores of 11.5 cm diam. and 12.0 cm deep were given the same fertilizer treatment as the microplots, placed in gas-tight growth chambers for periods of 4 weeks starting at 0, 4, 8, 12 and 16 weeks after fertilizing, and used to measure gaseous losses of 15N. The effects of soil water content ranging from field capacity to waterlogged on these losses were studied on a second series of cores. The apparent recovery of fertilizer nitrogen and the recovery of 15N in plant tops were usually well below 20%, and the recovery of 15N in the soil-plant system of the microplots was always below 50% of the amount applied. Most of the loss of 15N occurred during the first 4 weeks. A large part of the 15N lost from the field microplots was not traced, but the results demonstrated that surface run-off and leachate should not be ignored during nitrogen balance studies on pastures in south-eastern Queensland. Surface run-off generally removed less than 5% of the 15N, but the loss was 40% from one microplot. Losses due to leaching were not quantified, but a small significant excess of 15N in soil layers below 60 cm suggested that they did occur. Gaseous losses of 15N from waterlogged pasture cores reached 27%, but they were small or absent from cores with a soil water content at or below field capacity. Detailed work in the gas-tight growth chambers to define the soil conditions associated with gaseous losses of nitrogen are needed to relate laboratory findings to field conditions.

The effect of plant structure on the intake of tropical pastures. II.* Differences in sward structure, nutritive value, and bite size of animals grazing Setaria anceps and Chloris gayana at various stages of growth

Bite size (organic matter content per bite) of cows grazing swards of Chloris gayana (rhodes) and Setaria anceps (setaria) regrown for 2, 4, 6, and 8 weeks was measured using oesophageal fistulated animals. Sward canopy structure was measured by stratification into five vertical layers, each 15 cm high; for each layer weights of leaf and stem components were estimated. Chemical composition and in vitro digestibility of plant fractions and oesophageal fistulae samples were determined. Cows grazing the 4 week regrowths of rhodes grass had a larger bite size (0.32 g OM/bite) than when grazing 2 week regrowths (0.27 g OM/bite) when the availability of herbage and leaf material was lowest. Despite a marked increase in herbage yield as the pastures matured (up to 8427 kg/ha) the mean bite size decreased to a mean of 0.15 g OM/bite at 6 and 8 weeks. The bite size of cows grazing setaria pastures was lower than on the rhodes grass pastures but followed a similar pattern. A high density of leaf within the sward (sward leaf density) as well as a low stem content were considered to be the main factors affecting bite size. Setaria and rhodes grass pastures had both low sward bulk densities (a range of 14–96 kg/ha cm) and low sward leaf bulk densities (a range of 12–43 kg/ha cm) compared with temperate pastures. Basal layers of the sward contained more dense herbage (up to 148 kg/ha cm), but sward leaf density was usually less than 80 kg/ha cm and apparently inaccessible. ___________________ *Part I, Aust. J. Agric. Res., 24: 809 (1973).