Chemistry Reference
In-Depth Information
differences in performance between adjoining farms. A fundamental constraint
in many irrigated systems is the uncertainty in growing season weather; this is
also a factor in rain-fed systems where interactions between water and nutrient
availability are complex.
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Raising yields above 80% of yield potential is
possible, but only if technologies can be developed and adopted that reduce the
uncertainties faced by farmers in assessing soil and climatic conditions, or
respond dynamically to these conditions, or both (for example, installation of
nutrient and water sensors).
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Such technologies may have the added benefits
of increasing the efficiency of use of inputs and reducing losses off-site as well
as increasing yields.
Analysis of global wheat, maize and rice production found that yield gaps
were significantly correlated with irrigation, market accessibility and influence,
availability of agricultural labour, and slope; the contribution of these factors
varied substantially between regions and generalisations as to the best means
of reducing yield gaps were not possible.
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In China, the potential to reduce
yield gaps of maize was demonstrated on 66 on-farm experimental plots,
raising yields to 13 t ha
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on average (nearly twice the typical farmer yield)
without any increase in N fertiliser application.
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The demonstration of this
potential was achieved using simulation models to identify appropriate
combinations of planting date, crop density and cultivar at each site, based
on long-term weather data, and then changing variety, sowing date and
spacing as appropriate. This was combined with an in-season management
strategy for nitrogen fertiliser that resulted in a greater proportion of the
currently applied fertiliser being applied later in the growing season. This
integrated agronomic approach, combined with cultivars of appropriate
duration, increased yields and reduced off-site nutrient movement.
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In
addition to technological changes, other social and educational factors also
contribute to the ability to increase yields. For example, an analysis of yield-
gaps for rice in four intensively cropped regions in Indonesia, The Philippines,
Thailand and Vietnam demonstrated that the farmers with the best yields were
typically more educated and used fertilisers and labour more efficiently than
others.
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The importance of narrowing the yield gap between the average and
the best farmers was highlighted by the conclusion that were this to be
achieved then the resultant production would meet the projected increased
demand by 2050 (assuming no change in diet) in all countries except the
Philippines where other institutional changes would also be required.
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4 Opportunities for Sustainable Increases of Yield
The intensification of crop and animal production systems to meet human
demands for food has often been achieved at some cost to other ecological
goods and services. For example, excessive nutrient inputs, especially of
nitrogen and phosphorus, have resulted in coastal eutrophication and reduced
the quality of water in reservoirs used for drinking water.
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Similarly,
cultivating soils for crop production has often increased the frequency of
