Optimization offarm technologies and soil resources

Soils and prevailing agricultural production systems strongly interact with climate and climate variations, so farm technologies and management options have to be adapted to maintain soil functions for crop production to secure sustainable agricultural production as a basis for the welfare of many countries. Soil types in their current form developed over many centuries are determined among other factors by the climatic conditions. Agricultural practices can strongly impact on soil functions in the short term, and farming technologies and management can play an important role in these processes. In manyregions with extreme weather conditions, for example, soil functions can react very quickly to agricultural practices. Unfortunately this can lead to rapid and irreversible degradation of soil functions and further to desertification, which has become a significant problem in many agro-ecosystems in the world.

For example, improper irrigation schemes and use of salinated irrigation water can lead to increasing salinity of soils, making them unusable for agricultural production. ttis process is well known from badly adapted production systems as a result, for example, of long-term inappropriate policy (as was the case with Soviet cotton production concentrated in Central Asia). Other examples are overgrazing in the Sahel zone and other semi-arid regions for various reasons, leading to wind erosion and desertification. Crop productionof not suitable crops in warm semiarid zones with frequently strong winds can easily lead to wind erosion triggered by soil degradation (for example, short-term profit-driven agriculture as with the wheat production in Western Australia in earlier times). In tropical regions the high soil temperatures combined with high precipitation cause high decomposition and leaching rates and an inappropriate change in soil use for agricultural crop production can lead to fast soil degradation (for example, with too few organic matter residues or manure), (Sivakumar et al. 2005). In climates with frequent extreme precipitation events, such as the Asian monsoon regions, soil water erosion, especially in hilly terrains, has already caused enormous soil degradation, ttis is the case especially with production systems where the soil surface is not always fully covered or there are no terrace systems, as in the tea plantations of Sri Lanka.

ttere are many other examples showing how agricultural practices that are not adapted to local climatic conditions have led to irreversible damage to agricultural soils. Under climate change and changing climate variability, these problems will become an even more significant threat for the soils in many agroecosystems through increasing évapotranspiration rates for irrigated regions (Yeo 1999), more frequent droughts or extreme precipitation, for example.

Since farming is carried out by humans, soil cultivation plays an important role in crop production, tte first important aim was to control weeds and to optimize root growth conditions, ttis is still an important argument for ploughing in many agricultural areas and in ecological farming. However, because soil cultivation is an important cost factor, many options have been developed to decrease it, such as reduced soil cultivation or minimum to no soil cultivation and tillage systems. Furthermore, these systems can reduce soil water and wind erosion significantly and also increase soil water-holding capacity and infiltrability. It has been shown experimentally that increasing soil water-holding capacity by reducing soil cultivation in combination with mulch has had a significant positive yield effect (on cereals in the semi-humid region of eastern Austria in years with drought episodes, for example).

Similarly, simulation studies have shown that increased initial soil water content at the beginning of the growing season has a significant positive long-term yield effect (Trnka et. al., 2004); (Fig. 10.4). However, for larger field sizes these systems are mainly used with medium- and high-input systems where complex machinery is required. Often, soil fertility and functions could be improved and erosion reduced significantly by using these systems, which would make an important contribution to sustainable crop production. In ecological farming, however, ploughing still remains an important measure because of its weed control function. Nevertheless, minimum tillage and reduced soil cultivation can also be used under certain conditions in these systems.

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- -o ■ 1xC02 yield coefficient of variance - o- 2xC02 yield coefficient of vanance

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Fig. 10.4. Sensitivity of water-limited spring barley (cultivar Akcent) grain yield to different levels of initial available soil water (ISAW) in a highly fertile region under present and 2xCÛ2 climatic conditions (both ambient CO2 increase and changed climate were considered). Each point represents a 99-year simulation described by the mean and the value of the coefficient of variance.

tte most widespread decrease in appropriate soil functions for crop production such as water-holding capacity and soil fertility is caused by wind or water erosion. Soil erosion can have multiple causes, one of which is climate and climate variability in the form of extreme precipitation or strong winds in dry conditions. Farming practices and technologies have a strong impact on the climate-based potential for soil erosion, ttere are many examples of soil erosion caused, for example, by overgrazing in semi-arid regions with sandy soils or by growing slowly developing crops causing reduced soil cover for long periods, ttis is the case with maize, soybean or sugar beet also in temperate regions with significant extreme precipitation events.

Changes in crops or crop rotation to adapt to changing climate and variability may therefore impact indirectly on soil erosion in vulnerable regions (Rounsevell et al., 1999). Climate change and climate variability may also indirectly affect soil erosion. For example, O'Neal et al. (2005) report that increasing precipitation and decreasing cover from temperature-stressed maize are important factors for increasing soil erosion in the Midwest of the United States of America. In almost all agroecosystems soil erosion, caused be various factors, leads to a decrease in soil fertility and hence to a reduction in crop productivity because of loss of organic matter, nutrients and lower water-holding capacity. In temperate regions with high-input systems heavy machinery, often in combination with slowly developing crops and soil cover, contributes to soil compaction, decreasing water infiltration, increasing runoff and therefore water erosion. In Europe these problems are apparent with sugar beet and maize, where soils are not covered for a long time in spring and heavy machinery has a devastating and often irreversible affect on soil structure during the frequentlywet harvest periods in the autumn, ttis problem accelerates with increasing slopes of fields, as are frequently found in Europe.

Perennial crops in various climatic regions such as vineyards, orchards, tea or coffee, which are often grown in hilly regions, are also subject to water erosion, especially during extreme precipitation events. Mulching technologies such as grass or straw mulch or other crop residues are therefore often applied and are sometimes mandatory. In some cases, even the more costly or manpower-intense terrace systems have been re-established in order to stop long-term soil erosion.

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