Components of the water balance of an alley cropping system were measured to assess the extent to which tree rows 30 m apart with access to a fresh, perched watertable at 5 m depth were able to capture deep drainage from an inter-cropped cereal–legume rotation. Neutron probe data showed that the 4-year-old trees, cut back to 0.6-m high at the beginning of the experiment, depleted soil water to 2, 4, and 8 m laterally from the tree rows in their first, second, and third years of coppice regrowth, respectively. Combining data from soil water depletion in summer and comparisons of deuterium: hydrogen ratios of groundwater, xylem sap of trees, and herbaceous plants, it was shown that tagasaste trees drew on soil water for 80% of their transpiration in the first winter and 40% in the second, while switching to near total dependence on groundwater each summer and early autumn. Tree water use on a whole plot basis was 170 mm in 1997 (68% from groundwater) v. 167 mm in 1998 (73% from groundwater). Recharge to the perched watertable was estimated to be 193 mm under sole crop in 1998 (52% of rainfall), reducing to 32 mm when uptake of groundwater by trees was included. The degree of complementarity between tagasaste trees and crops in alley cropping used for water management is quantified for 1998 by calculating the ratio of the distance over which trees reduced drainage to zero to the distance over which they reduced crop yield to zero. It is concluded that segregated monocultures of trees and crops would be a more appropriate strategy than a closely integrated system such as alley cropping in this case.
Soil water management is typically by trial and error among smallholder farmers. Social learning in the use of farmer—friendly soil-water and nutrients monitoring tools were promoted in Malawi to improve productivity. A simple tool (chameleon) which was designed to fit the mental model of African farmers and to give an output that is linked to action was deployed to 198 farmers in nine irrigation schemes. Chameleon illustrates information on soil moisture status by colours—blue, green and red colours representing adequate moisture, moderate and dry soil status, respectively. The use of colours and not numbers promoted inclusiveness across illiterate and all gender categories. Farmers participated in sensors' installation, soil moisture measurement, data visualization and learning by doing to get insights from their participation. The chameleon was combined with an on-line communication and learning system to improve water management at scheme level. The results indicated that: (1) the tool gave farmers new frames of reference; (2) it improved farmers on time, labour and water saving by reducing irrigation intervals; (3) it gave farmers new reference of experience to change their irrigation traditions; (4) it also reduced conflict for water in irrigation schemes between users apart from improving water productivity. Use of these tools made a rigor that make scientists easily communicate science to lay farmer and initiated the movement of farmers who know how to manage water. Social learning in sensor technology helped to increase farmers' resilience to climate change and shaping the science of the future.
Adaptive management is the problem-solving approach of choice proposed for complex and multistakeholder environments, which are, at best, only partly predictable. We discuss the implications of this approach as applicable to scientists, who have to overcome certain entrained behaviour patterns in order to participate effectively in an adaptive management process. The challenge does not end there. Scientists and managers soon discover that an adaptive management approach does not only challenge conventional scientific and management behaviour but also clashes with contemporary organisational culture. We explore the shortcomings and requirements of organisations with regard to enabling adaptive management. Our overall conclusion relates to whether organisations are learning-centred or not. Do we continue to filter out unfamiliar information which does not fit our world view and avoid situations where we might fail, or do we use new and challenging situations to reframe the question and prepare ourselves for continued learning? Conservation implications: For an organisation to effectively embrace adaptive management, its mangers and scientists may first have to adapt their own beliefs regarding their respective roles. Instead of seeking certainty for guiding decisions, managers and scientists should acknowledge a degree of uncertainty inherent to complex social and ecological systems and seek to learn from the patterns emerging from every decision and action. The required organisational culture is one of ongoing and purposeful learning with all relevant stakeholders. Such a learning culture is often talked about but rarely practised in the organisational environment.
Irrigation development in Sub-Saharan Africa has lagged significantly behind that in other developing countries. Consequently, economic development and food security are also lagging behind. Since the mid-2000s there has been a resurgence in the willingness to invest in irrigation, and Sub-Saharan Africa has the largest potential of any developing region to benefit from it. However, to gain from new investment in irrigation without repeating past failures, it is critical to develop a business model for small-scale irrigation schemes. This article explores the barriers that such a model needs to address to be successful and the opportunities this represents for irrigators' profitability.
Summary. Permanent raised beds coupled with reduced tillage and cover crops are part of the Australian processing tomato industry’s strategy to move towards more sustainable farming practices. As a consequence, crops may be planted into denser soils. Previous work showed that processing tomatoes had considerable tolerance to no-tillage; mild soil compaction reduced vegetative growth but not fruit yield. This field study showed that severe compaction not only reduced vegetative growth, but also extended the duration of the exponential vegetative growth period, so that fruit and vegetative growth were competing for assimilates. Under these conditions, fruit yield was severely reduced. Accurate management of drip irrigation could not compensate for the narrow, non-limiting water range of a compacted soil. Mild water deficits during the late flowering and early fruit growth phase also reduced fruit yield. Pot experiments under controlled conditions revealed an interaction between soil fumigation and tillage management. Soil fumigation improved shoot growth at high and low soil densities with the greatest effects observed below ground; root length was more than doubled when soil cores with a bulk density of 1.79 t/m3 were fumigated. A cover crop of subterranean clover, grown in the off-season winter period, had no effect on fruit yield under non-compacted conditions. The implication is that cover crops, which have been shown to ameliorate adverse soil physical conditions, can only express their potential when soil conditions in a conventionally managed system are suboptimal.
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