Grain β‐glucan content is the most important attribute for barley (Hordeum vulgare L.) varieties destined for the human food market. This trait is important because of the blood glucose and cholesterol‐reducing properties of β‐glucans. High levels of grain protein content, test weight, and seed size and endosperm color may also add value. Seed yield potential, in part, determines the economic feasibility of producing human food varieties. To determine the potential of food barley production in the dryland production areas of the Pacific Northwest of the United States, 33 cultivars and advanced lines reported to vary in β‐glucan content were grown in 2006 and 2007 at two locations in northeastern Oregon under dryland cropping conditions. Seed yield, test weight, percentage of plump kernels, grain β‐glucan, and grain protein were measured on replicated samples from the four environments, allowing for assessment of average performance as well as genotype × environment interaction. Estimates of variance components showed that ∼66% of the variability in β‐glucan content was attributable to genotype. Cultivars and lines with waxy starch had an average β‐glucan value of 55 g kg−1 compared with 35 g kg−1 for cultivars and lines with nonwaxy starch. We found significant two‐ and three‐way interactions, but these accounted for much less of the total variation in the measured phenotypes than the main effects of variety, year, and location. Hulless accessions produced an average of 3580 kg grain ha−1 compared with 4260 kg grain ha−1 for the hulled accessions. Hulled, waxy‐starch varieties appear to have the greatest agronomic potential for dryland production, as they combine high yield potential and grain β‐glucan percentage.

This chapter briefly describes the individual effects of tree-crop interactions (soil fertility improvement, soil conservation, microclimate improvement and competition) and suggests how these may be quantified.

What are the main factors that govern the build-up of soilborne pathogens? 2. Which strategies can be followed to avoid outbreaks of soilborne diseases? 3. How can agroforestry be a tool in the management of soilborne disease problems? 15.1. Introduction Soilborne organisms (such as plant parasitic nematodes, fungi, bacteria, phytoplasma, protozoa and viruses) are among the most underestimated of the factors which affect plant productivity in tropical regions. Because of their microscopic size and the non-specific symptoms of an infection, these organisms live out of sight and, generally, out of mind of the growers and plant protection workers. Root-knot nematodes are an exception in that they cause distinctive symptoms in the form of root galls, which are sometimes referred to as 'root elephantiasis' by subsistence farmers in central Kenya (Fig. 15.1a). Otherwise, most farmers and extension staff are not able to identify nematodes and other soilborne diseases (Sharma et al., 1997). Moreover, interactions commonly occur between nematodes and other soil pathogens, complicating any quick recognition of the problem and assessment of the damage done. Soilborne plant pathogens affect plants primarily through the infection of roots. These organisms occur as complexes in soils and in plant tissues, the nature of which are generally poorly understood and little quantified. In addition to pathogenic and parasitic organisms 1 , the soil contains a wide range of competitor saprobes, antagonists, beneficial organisms, yeasts, bacteria and nematodes (Fig. 15.2). The population size of each of these groups is determined by edaphic and environmental factors, as well as by the availability of host roots. Many vegetables, cocoa, citrus, tobacco Lupinus spp. Eucalyptus spp.; Pinus spp. P. americana ; Macadamia spp.; citrus Armillaria mellea (root rot) Coffee, tea, root and tuber crops C. cajan Acacia spp.; Erythrina spp.; Grevillea robusta Annona spp.; Macadamia spp.; Vitis spp.

The concepts and models that can be used to explore how and where multispecies agroecosystems may be able to improve the use of plant growth resources, are presented, using experience gained from recent agroforestry research. The complex interactions that occur between tree and crops are discussed. The influence of resource availability on competition between plants is examined. The simple rules governing the success or failure when mixing trees and crops is outlined.

Forests are the biggest users of water worldwide and extensive forested areas have been lost or are undergoing conversion to agriculture, creating concerns about loss of hydrological functions and increasing the competition for scarce water between agriculture, urban centres, industries and wildlife. The challenge is to improve the sustainability and productivity of land and water use, especially for the growing populations of many developing countries. In this chapter we review recent findings on the hydrology of forests and agroforestry systems and indicate how modifications in treebased systems might increase water productivity.In forestry, the focus of research has moved from the hydrological functions of upland forest reserves that are close to settlements to a greater recognition of the roles played by upland communities in the management of water resources. A major source of conflict over water resources is the contrasting perceptions of 'watershed functions' between forest managers and local people, which are often based more on myths of forest functions than on science -for example, the idea that forests increase rainfall. These myths continue to dominate the views of policy makers and institutions and should be revised. The challenge is to gain a better insight into how farmer-developed land-use mosaics have modified watershed-protection functions. Priority must be given to the perceptions, experiences and strategies of local communities.Trees on farms have the potential for improving productivity in two ways. Trees can increase the amount of water that is used on farm as tree or crop transpiration. Trees can also increase the productivity of the water that is used by increasing biomass of trees or crops produced per unit of water used. Plot-level evidence shows that improvements in water productivity as a consequence of modifications to the microclimate of the crop are likely to be limited. Instead, evidence from semi-arid India and Kenya showed that the greater productivity of agroforestry systems is primarily due to the higher amount of water used. Almost half of the total water use occurred during the dry season, when cropping was impossible, and the rest was extracted from soil reserves. This implies a high temporal complementarity between the crop and tree components of the landscape mosaic. Research is needed to examine the impact of the increased water use on the drainage and base flow at the landscape level. This chapter also describes some of the technical approaches that can be used to improve land and water management, the role of trees and its relation to hydrology and the challenges for rational land-use decision-making.