Land-use change impacts on soil processes : tropical and savannah ecosystems

Land-use change impacts on soil processes

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Global drivers of plant pest problems include intensification of cropping which provides greater host availability for pests, international trade and food aid that increases the movements of plants and often their accompanying pests, migration and tourism that increase movement of people who carry plant materials, and civil conflict and war, that both increase movement of refugees and military personnel and disrupt phytosanitary control systems at borders FAO, Climate change as a driver will have different effects on the various types of pests Garrett et al.

Based on studies of individual species, climate change may affect: pest developmental rates and numbers of pest generations per year; pest mortality due to cold and freezing during winter months; or host plant susceptibility to pests Burdon et al. When two or more species contribute to a pest problem, as with vectored pathogens or pathogens which cause more severe symptoms in the presence of simultaneous insect damage, the effects of climate change could be expressed through any of these species Ghini, ; Garrett et al.

As if the inter-relationships between plants, pest organisms, and the existing environment weren't staggeringly complex, the onus of potential global climate change bodes yet further complications of the fragile equation Ghini, Examples of management practices for greenhouse gas emission reduction and soil carbon sequestration.

No-tillage is presumed to be the oldest system of soil management. In some parts of the tropics, No-tillage is still practiced as part of slash-and-burn agriculture.

After clearing an area of forest, by controlled burning, seed is placed directly into the soil. However, as mankind developed more systematic agricultural systems, cultivation of the soil became an accepted practice as a means of preparing a more suitable environment for plant growth. Paintings in ancient Egyptian tombs portray farmers tilling their fields using a swing-plough and oxen, prior to planting. No-tillage can be defined as a crop production system where soil is left undisturbed from harvest to planting except for fertilizer application.

Conversion of native vegetation to cultivated cropland under conventional tillage system has resulted in a significant decline in soil organic matter content Paustian et al. Furthermore, tillage can leave soils more prone to erosion, resulting in further loss of soil C Bertol et al.

Land-use change impacts on soil processes in tropical and savannah ecosystems

There is considerable evidence that the main effect is in the topsoil layers with little overall effect on C storage in deeper layers Six et al. Globally, at present, approximately 63 million ha are under no-tillage systems with USA having the largest area Lal, The underlying land management principles that led to the development of no-tillage systems in Brazil were, prevention surface sealing caused by rainfall impact, achievement and maintenance of an open soil structure and reduction of the volume and velocity of surface runoff. Consequently, the no-tillage strategy was based on two essential farm practices: i not tilling and ii keeping soil covered at all times.

This alternative strategy quickly expanded to different states and the planted area under no-tillage has since then increased exponentially. In the early 90's the area covered by the system was 1 million ha increasing 10 times by Now, the approximately 20 million ha covered by no-tillage practice Febrapdp, make Brazil the second largest adopter in the world. Changes in soil C stocks under no-tillage have been estimated in earlier studies for temperate and tropical regions.

Reicosky et al. Lal et al. For the tropical west of Nigeria, Lal observed a 1. In the tropics, specifically in Brazil, the rate of C accumulation has been estimated in the two main regions under no-tillage systems south and centre-west regions. Bayer et al.

Land-use change impacts on soil processes Francis Q Brearley

Corazza et al. Estimates by Amado et al.

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Other studies considering no-till system carried out in the centre-west part of Brazil Lima et al. Bernoux et al. However, the authors stressed that caution must be taken when analyzing no-till systems in term of carbon sequestration. Comparisons should include changes in trace gas fluxes and should not be limited to a consideration of carbon storage in the soil alone if the full implications for global warming are to be assessed.

As mentioned before, the no-tillage system in Brazil can vary significantly between regions. Therefore, we have used in our calculations of additional soil C accumulation due to non-tillage a weighted average value of 0. The total area in Brazil under the no-tillage system is about 20 million ha, and the weighted average soil C accumulation rate due to no-tillage adoption is 0. It is important to mention that there is a lot of controversy regarding whether no-till really does sequester much soil C, especially when the whole soil profile is considered Smith et al.

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Most studies that have looked at the whole profile have shown insignificant soil C gain. The quantity of residues returned, variations in the practices implemented and perhaps the type of climate are factors likely to influence the outcome. According to Smith et al. Burning versus non-burning harvesting sugar cane system. The sugar cane crop offers one of the most cost-effective renewable energy sources that are readily available in developing countries Macedo, It is a highly efficient converter of solar energy and, in fact, has the highest energy-to-volume ratio of all energy crops Johnson, Sugar cane is a perennial crop that is harvested on an annual cycle.

There may be up to six cycles before re-planting. There is generally only a short fallow between ploughing out the old cane and re-planting. It is a highly flexible resource, offering alternatives for production of food, feed, fibre and energy. Such flexibility is valuable in the developing world where fluctuations in commodity prices and weather conditions can cause severe economic hardships.

For biomass energy production, sugar cane is an excellent feedstock in terms of efficiency and flexibility, providing gaseous, liquid and solid fuels Ripoli et al. It offers the potential for climate change mitigation through substitution of fossil fuels without the need for excessive subsidies or expensive infrastructure development Oliveira et al.

The Brazilian ethanol programme remains the world's largest CO 2 mitigation programme Johnson, ; Oliveira et al.

At present in Brazil, sugar cane is cultivated on about 5 million ha, with an average annual production of approximately million tonnes FNP, There are two procedures adopted for sugar cane harvesting. Traditionally, sugar cane was burnt in the field a few days before harvesting in order to facilitate manual cutting by removing leaves and insects Thorburn et al.

However, since May this common practice has been progressively prohibited by law in some areas in Brazil. Even though the law will not be fully implemented before , the adoption of mechanical harvesting has increased exponentially in Brazil during the last decade. By the return of crop residues to the soil surface the mechanical approach has indirectly favoured soil organic matter accumulation Thorburn et al. The net contribution of the Brazilian sugar cane industry to the evolution of atmospheric CO 2 is a combination of three activities, two industrial and one agricultural.

The first activity is the substitution of gasoline as a fuel by alcohol. Since the early 's the Brazilian government has given incentives for alcohol production from sugar cane to be added to gasoline in the transportation sector Sociedade Nacional de Agricultura, Due to the oil crises in , Brazilian authorities created new incentives through the Brazilian alcohol program Proalcool to increase the production of alcohol to During to , million m 3 of hydrated alcohol and 71 million m 3 of anhydrous alcohol were produced.

Considering that 1 m 3 of gasoline can be substituted by 1. However, the alcohol production and consumption are increasing every year in Brazil. If data just for the last 10 years were used, the offset would be about 10 Mt C yr The second associated mitigation factor in the sugar cane system is related to the use of plant residues as a fuel. At the mill, the cane stalks are shredded and crushed to extract the cane juice while the fibrous outer residue, known as bagasse, is burnt to provide steam and electricity for the mill Luca, For instance, in approximately 45 Mt dry matter of sugar cane residues were produced in Brazil Brasil, Assuming that 2.

This renewable energy resource, found mainly in developing countries, has obvious appeal for international efforts to reduce carbon dioxide emissions. Moreover, the organic wastewater stream from alcohol production, known as vinasse, can be used as fertilizer or can be converted to methane gas through anaerobic digestion. The transportation fleets used in sugar factories and ethanol distilleries in Brazil have in some cases been powered by methane gas Johnson, The production of alcohol has been viewed as a valuable means of saving foreign exchange in developing countries while at the same time providing local and global environmental benefits Oliveira et al.

In addition to climate mitigation and reduction of local pollutants, it can serve as an octane enhancer that might speed the phasing-out of leaded gasoline. The economic and environmental attractiveness of sugar cane as a renewable energy resource and the variety of options for increasing use of cane by-products and co-products could one day lead to sugar becoming the by-product rather than the main product.

Finally, the third activity associated with CO 2 mitigation in the sugar cane system is the conversion harvesting without prior burning. In the absence of burning, sugar cane residues are returned to the soil surface with litter and this factor is significant because it contrasts with the alternative system where cane is burnt before harvest removing dead and green leaves, so there is very little C returned to the soil from the above ground vegetation. For instance, Blair et al. In Southern Brazil, Feller reported that an average of 0. Other estimates exist, but for shorter periods of no-burning.

For instance, Luca reported increases ranging from 2 to 3.

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The corresponding annual increase ranges from 0. However, sugar cane is typically replanted each years and tillage practices are then commonly used. This procedure would probably reduce the high rates presented by Luca if the study had been for a longer period. In our estimate of C sequestration we have used the value found by Feller because it represents the longest period of harvest without burning in Brazil and incorporates cane replanting.

Thus, considering the area under this management system and the mean annual C accumulation rate, a total of 0. When sugar cane is burnt other greenhouse gases like CH 4 and N 2 O are emitted to the atmosphere. Macedo shows that 6. Considering the total area with sugar cane under no burning harvesting system 1. The same calculation is required for N 2 O emission; however, currently there are no adequate measurements of this gas for sugar cane.

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