William D Bellotti

Distribution, abundance and symbiotic effectiveness of Rhizobium leguminosarum bv. trifolii from alkaline pasture soils in South Australia

The current dissatisfaction with low productivity of annual medic (Medicago spp.) pastures has highlighted the need to seek alternative legumes to provide efficient N2 fixation in low rainfall, alkaline soil environments of southern Australia. Clover species adapted to these environments will have limited N2 fixation if effective rhizobia are not present in sufficient quantities. A survey of 61 sites was conducted across South Australia to determine the size, distribution and effectiveness of Rhizobium leguminosarum bv. trifolii (clover rhizobia) populations resident in these low rainfall, alkaline soil environments. Clover rhizobia were detected at 56 of the sites, with a median density of 230–920 rhizobia/g soil. Most rhizobial populations were poor in their capacity to fix nitrogen. Rhizobial populations from fields provided 11–89% and 10–85% of the shoot biomass of commercial reference strains when inoculated onto host legumes T. purpureum (purple clover) and T. resupinatum (persian clover), respectively. Rhizobial population size was correlated negatively to pH and the percentage of CaCO3 in the soil, and was significantly increased in the rhizospheres of naturalised clover, found at 17 sites. Management options for rhizobial populations to improve legume diversity and productivity are discussed in terms of rhizobial population dynamics and likely soil constraints to successful rhizobial colonisation.

Quantitative and visual assessments of climate change impacts on South Australian wheat production

Abstract The outputs of Global Climate Models (GCMs) were nested with the DSSAT3.5 CERES-Wheat model to explore the potential effects of climate change on South Australias wheat production for the 2080s with CO2 fertilisation effect taken into account. A stochastic weather generator: LARS-WG was employed to generate daily climate change scenarios. The simulated results were fed into Arc/View to produce regional impact maps for visual assessment and spatial analysis under different climate change scenarios and CO2 levels through an interface of AEGIS/WIN. Two sowing dates were employed to look at the potential impact of future climate change and atmospheric CO2 increase on wheat production. Simulated results show that (1) Wheat yields increase under all CO2 levels. Yields increase under different climate change scenarios in most cases. However, the increase is less than that under corresponding CO2 levels due to the adverse effects of climate change. Wetter sites benefited less compared with drier sites under climate change scenarios. (2) Grain nitrogen content decreases under all CO2 levels and under most of climate change scenarios, but the decrease under climate change scenarios is less than that under corresponding CO2 level due to increased temperature which enhanced soil nitrogen mineralisation. Grain protein content decreased more at drier sites. The combined effects of climate change and increase of atmospheric CO2 concentration will downgrade wheat quality at least one class at drier sites. (3) Grain yield at planting date of 30 June was significantly enhanced compared with that of planting date of 30 May under the same environmental change condition (same climate change scenarios plus their corresponding CO2 levels).

An exploratory evaluation of APSIM to simulate growth and yield processes for winter cereals in rotation systems in South Australia

The Agricultural Production Systems Simulator (APSIM) suite of models was used to predict dynamics in water and nitrogen in soil, as well as the growth and yield of sequential crops of wheat and barley in pasture–wheat–barley rotations, between 1995 and 1997 at Roseworthy, South Australia. The NWHEAT model satisfactorily predicted above-ground dry matter, leaf area index and grain yields for both crops in rotations with either grassy (Grass) or medic (Medic) pastures, including the lack of significant response of yield to nitrogen fertiliser applied to wheat at sowing. Simulation data for soil water, from SOILWAT2, was consistent with measured data. Simulation with SOILN2, however, largely underestimated soil nitrogen, due to excessive uptake by the simulated wheat during the season when nitrogen was abundant and water supply readily available. Thus, the soil nitrate had to be reset at sowing for the following barley crop; simulated soil nitrate agreed with the measured data in this season when this nutrient was low. For most variables of crop growth and soil water, the simulated data were mostly within 2 standard errors of the measured means. Prediction of grain protein was underestimated in all cases, including where nitrogen in the shoot was overestimated. This was possibly due to inadequate remobilisation of nitrogen from the straw and roots to the grain by the simulated crop. A satisfactory prediction of dry matter, grain yield and grain weight was obtained for wheat when the models were extended to other trials at Roseworthy (Lower North), Minnipa (Upper Eyre Peninsula) and Wunkar (Murray Mallee), based on limited soil data. Long-term simulations of wheat yields showed that, with early sowing in the Lower North, median wheat yield increased by 50 kg/ha for every kilogram of nitrogen applied at sowing, up to a maximum nitrogen rate of 50 kg/ha. In the drier districts of the Upper Eyre Peninsula and the Murray Mallee, nitrogen fertiliser of no more than 25 kg/ha, applied at sowing, was enough to achieve yield benefits in any given season. At these drier sites, crop failures occurred in 5% (Upper Eyre Peninsula) and 10% (Murray Mallee) of the seasons simulated. Median sowing dates from these simulations were 15 May for the Lower North, 30 May for the Upper Eyre Peninsula and 24 May for Murray Mallee. This suggested that sowing could be conducted at least a week earlier than currently practised in the 3 environments. This study demonstrated the capability of APSIM to predict growth and grain yield of wheat and barley, as well as the associated dynamics of soil water in the main cereal belts of South Australia.

Supplementary feeding with grain improves the performance of sheep grazing saltbush (Atriplex nummularia) in autumn

Merino wethers aged 1.5 years grazed a saltland pasture comprising old man saltbush (Atriplex nummularia) with an inter-row of senesced grasses and medic for 6 weeks in autumn, in a cereal–livestock zone with a Mediterranean-type environment in South Australia. The experimental treatments were a control (old man saltbush, SB), supplementation with 250 g/sheep.day barley straw (SB + S), supplementation with 250 g/sheep.day barley grain (SB + G) and supplementation with 250 g/sheep.day barley straw + 250 g/sheep.day barley grain (SB + S + G). The sheep in SB + G finished the experimental period significantly heavier (53.6 kg, P < 0.001) than SB (51.0 kg), SB + S (50.5 kg) or SB + S + G (51.1 kg) animals. Feeding grain also increased length of wool grown daily by 16% and would have increased the value of the sheep by being able to sell them ‘out of season’ when prices are higher. Sheep supplemented with grain alone had a higher liveweight than those provided with grain and straw, a result that cannot be explained but may be associated with altered grazing behaviour. It appears that, while old man saltbush provides sheep with an acceptable intake of protein and minerals, the addition of a cereal grain supplement improves energy balance and optimises rumen protein capture to improve liveweight and wool growth performance.

Nitrogen fixation in annual Trifolium species in alkaline soils as assessed by the 15N natural abundance method

Annual clover species such as Trifolium purpureum Loisel., T. resupinatum L., and T. alexandrinum L. are adapted to alkaline soil conditions and provide certain agronomic advantages over annual medics (Medicago spp.). Annual clovers have not been widely grown in alkaline soils in Australia, and quantifying their dinitrogen (N(2)) fixation in alkaline soils is important in understanding their potential role in mixed farming systems of southern Australia. Using the (15)N natural abundance technique, it was estimated that annual clovers fixed 101-137 kg N/ha at Roseworthy and 59-62 kg N/ha at Mallala, on Calcarosols with soil pH of 8.0 and 8.5, respectively. Species differed in the percentages of fixed N2 estimated in shoot dry matter, which was highest in T. alexandrinum (77-85%), moderate in T. resupinatum (76%), and lowest in T. purpureum (65-74%). Naturally occurring soil rhizobia (Rhizobium leguminosarum bv. trifolii) provided adequate nodulation, as inoculation with different strains of rhizobia had little influence on nodulation or N(2) fixation. These results indicate that clovers can provide a significant contribution of fixed N(2) to mixed farming systems. Examination of nodules indicated variable nodule occupancy by the inoculant rhizobia and that 69% of shoot N was fixed when clovers were nodulated by the soil populations of rhizobia. A simple model is defined to identify the potential interactions between inoculated legumes and soil rhizobia, and the options for enhancing symbiotic effectiveness are discussed.

Direct and indirect land-use change as prospective climate change indicators for peri-urban development transitions

With urban areas responsible for a significant share of total anthropogenic emissions, greenhouse gas (GHG) emissions due to land-use change (LUC) induced by peri-urban (PU) development have the potential to be considerable. Despite this, there is little research into the transition from PU cropland to housing in terms of contribution to global warming. This paper presents a cross-sectoral integrative method for prospective climate change evaluation of PU LUC. Specifically, direct LUC (dLUC) GHG emissions from converting PU cropland to greenfield housing were examined. Additionally, GHG emissions due to displaced crop production inducing indirect LUC (iLUC) elsewhere were assessed. GHG impacts of dLUC and iLUC were each determined to be approximately 8 per cent of total GHG emissions due to a greenfield housing development displacing PU cropland. This magnitude of dLUC and iLUC emissions suggests that both have importance in future land-use decision making with respect to PU environments.

Improving the use of available feed resources to overcome sheep feeding deficits in western China

Socioeconomic and agro-ecological circumstances often compel smallholder livestock farmers in the developing world to maintain livestock over winter, and this can incur production penalties due to insufficient feed quality and availability. Recent policy efforts in western China have attempted to address this issue through the promotion of lucerne production to support growing livestock numbers with its high nitrogen content, however lucerne is underutilised by farmers and rarely maintained beyond harvest. The potential benefits to production of storing enough lucerne to meet the minimum nitrogen requirements of rumen function during the winter deficit were explored in an experiment in Qingyang Prefecture, Gansu Province, P.R. China. Tan weaner sheep (mean weight 15.4 kg) were fed corn straw, corn grain and lucerne hay in respective ratios of 80 : 20 : 0 [metabolisable energy (ME) = 7.4 MJ/kg DM, crude protein = 40 g/kg DM; ‘R1’] or 55 : 20 : 25 (ME = 8.2 MJ/kg DM, crude protein = 65 g/kg DM; ‘R2’). Rations were offered daily in a constant quantity that supplied ~80% maintenance energy requirements at the start of the experiment. Sheep fed R2 retained 0.7 kg more on average than those fed R1 (P 0.05). The results indicate that the capacity for underfed Tan weaner sheep to absorb energy from low protein rations typical of winter rapidly degrades and that the lucerne hay in the diet prevented this decline. Furthermore, these findings demonstrate that conserving lucerne for inclusion in winter rations is a potential strategy for smallholder farmers to maintain the digestive efficiency of Tan sheep during sustained underfeeding contributing to greater retention of liveweight on restricted diets.

The interplay of production commercialisation and specialisation : an empirical study on Chinese smallholders

Purpose - The purpose of this paper is to explore the endogenous relationship between production specialisation and market commercialisation with an empirical study of farmers in Northwest China. Design/methodology/approach - The three-stage least squares were used to address simultaneity and over-identification problems in comparison with two-stage least squares (2SLS). The Durbin-Wu-Hausman test was employed to identify the endogeneity of the commercialisation and specialisation variables. The validity, relevance, and strength of the instruments were tested using the Stock-Yogo weak instrument diagnostics test. Findings - A two-way interrelationship between specialisation and commercialisation were confirmed, and suggest that farmers’ decisions on farm commercialisation and production specialisation are actually separate and interacting. Social implications - By demonstrating that a virtuous cycle exists between agricultural commercialisation and on-farm specialisation, policies can be formulated to complement these two effects that may help increase small holders’ income. Farmers’ market participation can be indirectly improved by combining market improvement and risk management tools to encourage production specialisation. Originality/value - The insights of this study cast further light onto the farm market participation theory by emphasising that higher asset endowments enable small farmers to specialise in production with comparative advantage.

Variation in feed utilisation by sheep undergoing compensatory growth following underfeeding with and without additional dietary nitrogen in western China

Small mixed farming systems in developing economies often rely on compensatory growth to recover livestock weight lost during seasonal feed shortages; however, deficit feed management may continue to affect the capacity of livestock to efficiently use feeds even after adequate feeding has resumed. Accordingly, we compared the difference in liveweight gain and feed utilisation over time in Tan weaner sheep in western China, during a period of ad libitum compensatory feeding after alternative feed deficit scenarios. During the feed deficit period, sheep were offered, at 80% maintenance requirements, corn straw, corn grain and lucerne hay in a respective ratio of either 80 : 20 : 0 (S1 ration: metabolisable energy = 7 MJ/kg DM, crude protein = 40 g/kg DM) or 55 : 20 : 25 (S2 ration: metabolisable energy = 8 MJ/kg DM, crude protein = 65 g/kg DM) for 20 days. All sheep were then offered an ad libitum supply of the S2 ration for a further 20 days, during which DM digestibility (DMD), energy intake and liveweight was measured and compared at 5-day intervals. Results indicated that sheep previously fed the S1 ration were not able to digest as much of the ad libitum S2 ration as those previously fed the S2 ration, experiencing significantly lower DMD, energy intake and average daily weight gain. The difference in the effect of the two restrictive feeding treatments on the digestibility of the ad libitum S2 ration gradually decreased over time, indicative of a recovery adaptation during ad libitum feeding period. The rate of DMD recovery post-realimentation was greater in the S1 sheep, likely due to their significantly lower DMD values immediately following underfeeding. We concluded that the comparatively higher nutritive value of the S2 ration sustained rumen digestive function throughout the restrictive feeding period, permitting sheep to commence re-feeding under conditions that are more favourable. Additionally, it is evident that reliance on livestock winter rations typical in western China, as expressed by the S1 ration, degraded ruminant digestive conditions to such an extent that feed was used with reduced efficiency even after being supplied in adequate quantities.