Ian Nuberg

Effect of shelter on temperate crops : a review to define research for Australian conditions

The fact that the shelter created by windbreaks can have a significant, positive effect on crop production is supported by eight decades of research from many countries around the world. Although the concept of planting windbreaks to enhance crop production has general currency in Australia, the practice is not as wide as it could be. This review of the last decade of windbreak literature defines the research needed to encourage wider utilisation of windbreak technology. After outlining the principal mechanisms behind the effect of shelter on temperate crops, the review discusses relevant literature of the past decade especially that from Australia. The main mechanisms discussed are: the protection of crops from physical damage; soil conservation; the direct augmentation of soil moisture; and the alteration of the crop energy balance and plant water relations. Also discussed are the elusiveness of the shelter effect, competition from windbreak trees, and the modelling of windbreak systems. Suggestions for future research in Australia include: quantifying the competition of various windbreak species and the effect of root pruning on both crop and tree; a model of crop energy and water relations at the tree-crop interface; an economic model and a farmer-oriented decision support tool.

The Australian National Windbreaks Program: Overview and summary of results

This overview paper presents a description of the National Windbreaks Program (NWP) — its objectives, the main methods used to achieve these objectives and a summary of the key results. It draws these from the individual papers appearing in this special issue, which provide detailed descriptions and discussion about the specific research sites and research methods used, in addition to interpreting and discussing the results. The key findings were the following: (i) Two broad areas of crop and pasture response can be identified downwind of a porous windbreak: a zone of reduced yield associated with competition with the windbreak trees that extended from 1 H to 3 H, where H is the windbreak height, and a zone of unchanged or slightly increased yield stretching downwind to 10 H or 20 H. (ii) Averaged over the paddock, yield gains due to the effect of shelter on microclimate were smaller than expected — especially for cereals. Yield simulations conducted using the APSIM model and 20 years of historical climate data confirmed this result for longer periods and for other crop growing regions in Australia. Larger yield gains were simulated at locations where the latter part of the growing season was characterised by high atmospheric demand and a depleted soil water store. (iii) Economic analyses that account for the costs of establishing windbreaks, losses due to competition and yield gains as a result of shelter found that windbreaks will either lead to a small financial gain or be cost neutral. (iv) Part of the reason for the relatively small changes in yield measured at the field sites was the variable wind climate which meant that the crop was only sheltered for a small proportion of the growing season. In much of southern Australia, where the day-to-day and seasonal variability in wind direction is large, additional windbreaks planted around the paddock perimeter or as closely-spaced rows within the paddock will be needed to provide more consistent levels of shelter. (v) Protection from infrequent, high magnitude wind events that cause plant damage and soil erosion was observed to lead to the largest yield gains. The main forms of direct damage were sandblasting, which either buries or removes seedlings from the soil or damages the leaves and stems, and direct leaf tearing and stripping. (vi) A corollary to these findings is the differing effect that porous windbreaks have on the air temperature and humidity compared to wind. While winds are reduced in strength in a zone that extends from 5 H upwind to at least 25 H downwind of the windbreak, the effects of shelter on temperature and humidity are smaller and restricted mainly to the quiet zone. This means that fewer windbreaks are required to achieve reductions in wind damage than for altering the microclimate. (vii) The wind tunnel experiments illustrate the important aspects of windbreak structure that determine the airflow downwind, and subsequent microclimate changes, in winds oriented both perpendicular and obliquely to porous windbreaks. These results enable a series of guidelines to be forwarded for designing windbreaks for Australian agricultural systems.

Farmers’ assessments of private adaptive measures to climate change and influential factors: a study in the Mekong Delta, Vietnam

AbstractAdaptation to climate change in agricultural settings depends on understanding farmers’ perceptions of the nature of climate change, their agency in adapting and the efficacy of adaptive measures themselves. Such knowledge can improve mitigation and adaptation strategies. This study addresses the limited understanding of how farmers appraise their private adaptive measures and influential factors. It uses data from structured interviews with 598 rice farmers in the Mekong Delta, Vietnam. Based on protection motivation theory, farmers’ assessments of private adaptive measures were measured by perceived self-efficacy, perceived adaptation efficacy and perceived adaptation cost. Multiple regressions were used to understand significant factors affecting those assessments. Some demographic and socio-economic factors, belief in climate change, information and objective resources were found to influence farmers’ adaptation assessments. It is shown that the sources and quality of information are particularly important. The improvement of both the accessibility and usefulness of local services (e.g. irrigation, agricultural extension, credit and health care) is deemed a necessity for successful adaptation strategies in the Mekong Delta. The paper also shows the application of PMT in measuring farmers’ appraisals of private adaptive measures to climate change, thereby opening this area for further research.

Windbreak research in a South Australian cropping system

This paper presents the results of 3 years (1994-96) work on the effect of shelter created by a 9 m high Aleppo pine (Pinus halepensis) windbreak in the Mediterranean environment of South Australia on the productivity of wheat, canola, faba beans and oats. Elements of the classic windbreak signature could be detected in the yield responses of 6 of 8 crop years. For example, in the dry year of 1994, yields in the sheltered zone (3-6 H, where H is a multiple of windbreak height) were 44, 49 and 81% greater than in the exposed zone (18-24 H) for wheat, faba beans and canola, respectively. In 1995, a wet year, only faba beans showed a response (18% increase). In 1996, oats showed an apparent 25% yield increase in the sheltered zone compared with the unsheltered zone. However, these yield differences were not due to shelter alone. For example, covariate analysis of 1995 wheat and bean yield data with soil texture indicated that yield variation across the paddock could be explained by variation in depth to calcareous clay loam. Cumulative water use of wheat was greater in the 3-12 H zone in 1994 (dry year) but less in 1995 (wet year); however, these differences are likely to be also due to soil variation in the 2 plots used. Nevertheless, the windbreak effectively altered the microclimate. Cumulative temperature was measured at 4 distances on the leeward side of the windbreak and used to predict the time taken for wheat to reach anthesis at each location. The correlation between normalised values of observed and predicted times to anthesis was found for 3 wheat crops with different times of sowing in 1995 (r 2 = 0.62). It was concluded that (i) shelter will affect the physiology of crops grown in this environment, (ii) the shelter effect on enhancing crop yield is relatively subtle compared with other sources of yield variation and (iii) the evidence for a water-saving mechanism in enhancing crop yield is inconclusive.

Farmers’ Perceived Risks of Climate Change and Influencing Factors: A Study in the Mekong Delta, Vietnam

Many countries are confronting climate change that threatens agricultural production and farmers’ lives. Farmers’ perceived risks of climate change and factors influencing those perceived risks are critical to their adaptive behavior and well-planned adaptation strategies. However, there is limited understanding of these issues. In this paper, we attempt to quantitatively measure farmers’ perceived risks of climate change and explore the influences of risk experience, information, belief in climate change, and trust in public adaptation to those perceived risks. Data are from structured interviews with 598 farmers in the Mekong Delta. The study shows that perceived risks to production, physical health, and income dimensions receive greater priority while farmers pay less attention to risks to happiness and social relationships. Experiences of the events that can be attributed to climate change increase farmers’ perceived risks. Information variables can increase or decrease perceived risks, depending on the sources of information. Farmers who believe that climate change is actually happening and influencing their family’s lives, perceive higher risks in most dimensions. Farmers who think that climate change is not their concern but the government’s, perceive lower risks to physical health, finance, and production. As to trust in public adaptation, farmers who believe that public adaptive measures are well co-ordinated, perceive lower risks to production and psychology. Interestingly, those who believe that the disaster warning system is working well, perceive higher risks to finance, production, and social relationships. Further attention is suggested for the quality, timing, and channels of information about climate change and adaptation.

A rapid PCR-based diagnostic test for the identification of subspecies of Acacia saligna

Subspecific taxa of species complexes can display cryptic morphological variation, and individuals and populations can often be difficult to identify with certainty. However, accurate population identification is required for comprehensive conservation and breeding strategies and for studies of invasiveness and gene flow. Using five informative microsatellite markers and a Bayesian statistical approach, we developed an efficient polymerase chain reaction-based diagnostic tool for the rapid identification of individuals and populations of the Acacia saligna species complex of Western Australia. We genotyped 189 individuals from 14 reference populations previously characterised based on morphology and used these data to investigate population structure in the species complex. High total genetic diversity (HT = 0.729) and high population differentiation (θ = 0.355) indicated strong intraspecific structuring. With the provision of prior population information, the reference data set was optimally resolved into four clusters, each corresponding to one of the four main proposed subspecies, with very high membership values (Q > 97%). The reference data set was then used to assign individuals and test populations to one of the four subspecies. Assignment was unequivocal for all test individuals from two populations of subsp. lindleyi and for all but one individual of subsp. stolonifera. Individuals from populations of subsp. saligna and subsp. pruinescens showed a degree of genetic affinity for the two subspecies in their assignments, although the majority of individuals were correctly assigned to subspecies. The diagnostic tool will assist in characterising populations of A. saligna, especially naturalised and invasive populations of unknown origin.

Future of forest gardens in the Uvan uplands of Sri Lanka

Forest gardens are traditional agroecosystems in the humid tropics that have evolved a forestlike structure and as such are commonly thought to be a good example of sustainable agriculture. While this may be true in the sense of soil protection and maintenance of biodiversity, they are not necessarily maintainable in the context of competing land use in the landscape. Such appears to be the case of forest gardens in the uplands of Uva Province of Sri Lanka. This paper reports an agroecological analysis of forest gardens and other forms of land use in Uva, and discusses how this understanding can be used to make use of the good properties of forest gardens. It shows that although they have very real environmental and social benefits, they are unable to satisfy the material needs of a rural population undergoing demographic and cultural changes. However, the alternative land-use systems, both private smallholder and state owned, have serious deficiencies with respect to long-term sustainability, and it is essential to develop appropriate alternatives. It should be possible to design a smallholder farming system that incorporates the high productivity of market gardens (i.e., the cultivation of seasonal crops such as vegetables) with, at least, the high stability and biophysical sustainability of the forest garden. Considerable work still needs to be done on the design of such a system as well as the agency for its development and promotion. The paper treats the forest gardens of Uva as a case study from which some general conclusions can be drawn with respect to the conscious development of forest garden systems elsewhere in the tropics.

Maternal body composition in seedstock herds. 1. Grazing management strategy influences perspectives on optimal balance of production traits and maternal productivity

Seedstock breeders’ perspectives on topics associated with maternal productivity in beef cattle were investigated through the use of qualitative in-depth semi-structured interviews. Given the complexity of maternal productivity, it is possible that some issues may not be fully captured by recording performance and data analysis. This paper discusses theory emerging from content analysis of interview data on management and genetic factors affecting maternal productivity as detailed by seedstock breeders in southern Australia. Overall, 24 interviews were conducted as part of an intensive field-work component with seedstock breeders involved with the Cooperative Research Centre for Beef Genetic Technologies’ Maternal Productivity Project. Qualitative content analysis of interview data revealed a considerable divergence in attitudes to cow management with regards to grazing management, body condition fluctuation and the utilisation of body fat reserves. Specifically, production systems diverged on the basis of animal management characterised by either ‘controlled’ or ‘variable input’ feeding strategies. Variation in management approach was associated with different perspectives on the perceived importance of selecting for production traits including growth, beef yield and milk compared with selection for perceived resilience traits including increased subcutaneous fat. The results demonstrated that among seedstock breeders targeting similar end markets, substantial variation in animal selection and management exists and this requires further characterisation to ensure breeding programs and animal management are optimal.

Negative evaluation of conservation agriculture: perspectives from African smallholder farmers

ABSTRACT Despite more than three decades of promotion, conservation agriculture (CA) has not been widely adopted by smallholder farmer in sub-Saharan Africa. This low rate of adoption reflects substantial negative evaluation of CA by many smallholder farmers, the causes of which have not been adequately explored in an in-depth, qualitative manner. Hence, we implement the Livelihoods Platforms Approach to explore directly with negatively evaluating farmers the reasons why they chose not to implement CA using semi-structured interviews with 35 farmers from 23 communities in 6 African countries. While there are issues with perceived benefit and relevance, the primary driver of negative evaluation of CA was found to be the feasibility of implementation. The required resources to implement CA (financial, physical, human and informational) are limited by community and institutional constraints which appear unlikely to be overcome through interventions targeted at addressing household resources. More positive evaluation of CA by smallholder farmers requires: (1) development of financially viable CA adoption pathways; (2) incorporation of wider livelihood objectives into a CA ‘package’; (3) re-evaluation of current extension policy; and (4) development of CA-complementary agricultural policies. Without addressing these issues, the potential benefits of CA adoption are unlikely to be achieved in African smallholder systems.

Establishing woody perennials on hostile soils in arid and semi-arid regions – A review

Background and aimsWoody perennials can be difficult to establish on harsh soils in arid and semi-arid regions. Historically, technological advances have focussed on methods to improve transplanting and direct-seeding but the available information on these advances remains fragmented and the edaphic factors have been largely ignored. This review explores the literature on plant establishment and identifies soil properties that limit plant response in harsh environments.ConclusionsWe reveal that some woody perennials are particularly well-adapted to dry conditions and can also help reclaim degraded landscapes. Furthermore, the environmental and phenological factors that limit the success of direct seeding are well understood but the edaphic factors are not. For example, seedbed preparation and subsoil amelioration before seeding have not been evaluated in dry regions. Seed-priming and seed-placement are also poorly understood, as is the tolerance of woody perennials to different salt types in waterlogged soils of extreme pH and high soil strength. The reason why woody perennials can penetrate strong, hard soils is not obvious from the literature. They apparently cannot exert root growth pressures of the same magnitude as domesticated plants, so they must be able to exploit soil biopores and cracks more efficiently. Other gaps in our understanding of the soil factors that limit woody perennial establishment on hostile soils are identified.