Soil nutrient loss

What nutrient losses are predominant in soil degradation in your country Give examples and explain the reasons for soil nutrient losses. 

The removal of biomass, such as crop residues, from the land for energy production intensifies soil erosion, water runoff, and soil nutrient losses. In addition, the conversion of natural ecosystems into energy-crop plantations would alter and/or reduce the habitat and food sources for wildlife and biodiversity. 

Biomass Redistribution Associated with Deforestation and Fire. The influence of deforestation on biogeochemical cycles is dependent upon a number of factors associated with the unique characteristics of the ecosystem (climate, soils, topography, etc), the quantity of the total nutrient pool stored in aboveground biomass (Table II), and the level of disturbance (i.e. the degree of canopy removal, soil disturbance, and the quantity of wood or other forest products exported from the site). The quantity of biomass consumed by one or more slash fires following deforestation can also dramatically increase nutrient losses, influence post fire plant succession, and hence, postfire biogeochemical cycles. 

Much of the surface soil erosion and hence nutrient loss occurs when deforestation and biomass burning removes and/or consumes the organic materials that protect the soil surface. Significant losses may occur by dry ravel or overland water erosion associated with precipitation events. Under a shifting cultivation system in a tropical deciduous forest ecosystem in Mexico, Maass et al. 61) reported first year losses of N, P, K, and Ca were 187, 27, 31, and 378 kg ha" respectively. In contrast, losses in adjacent undisturbed forests were less than 0.1 kg ha for all nutrients except Ca (losses were 0.1-0.5 kg ha for Ca). 

In addition to a complete water balance, EPIC estimates plant biomass production, fertilizer use, wind and water erosion, loss of nitrogen and phosphorus from the soil, and the effect of nutrient loss from the soil on plant growth. 

The CEC of soil is important from two perspectives. First, it retards the leaching loss of important cations from soil. Each year, calcium and magnesium are leached out of the soil, causing soils in humid regions to become acidic. This increased acidity must be ameliorated by the application of limestone (CaC03). Second, exchangeable cations are available to plants, and this characteristic allows soil to serve as a store of important soil nutrients such as potassium, calcium, and magnesium. 

An adequate and balanced supply of nutrients in the soil is essential for several reasons. Nutrient surpluses might result in nutrient losses which subsequently could lead to water and air contamination (see chapter 3.2.2 and 3.2.3) and eutrophication. However, nutrient deficiency is synonymous with the overexploitation of soil nutrients in the long run and leads to a decrease in yield and product quality. 

Birk, L.A. and F.E.B. Roadhouse (1964). Penetration of and persistence in soil of the herbicide atrazine. Can. J. Plant Sci., 44 21-27. Blevins R.L., W.W. Frye, P.L. Baldwin, and S.D. Robertson (1990). Tillage effects on sediment and soluble nutrient losses from a Maury silt loam soil. J. Environ. Qual., 19 683-686. 

Blanco-Canqui, H., C.J. Gantzer, S.H. Anderson, and E.E. Alberts (2004). Grass barriers for reduced concentrated flow induced soil and nutrient loss. Soil Sci. Soc. Amer. J., 68(6) 1963-1972. 

Crop residue application can prevent erosion, reduce nutrient losses, stimulate microbial activity in the rhizosphere, improve soil structure and increase the yield of subsequent crops (Schlecht et al., 2006). It may contribute to SOM build-up, but rapid breakdown due to synchrony of high temperature and moist soil during the rainy season(s), together with termite activity, limits residual effects in savannah areas. Mulching with 2 t ha 1 of crop residue, the rate most frequently used on experimental plots, resulted in yield increases from less than 10% to manifold, depending on crop, management, soil and climate (e.g. Schlecht et al., 2006). 

Biomass development (Jordan 1985) and regeneration capacity (Uhl 1987) are not always clearly associated with differences in soil fertility, but they are certainly related to rates and patterns of nutrient cycling (Vitousek and Sanford 1986, Medina and Cuevas 1989, Tiessen et al. 1994b). On poor soils, nutrients may cycle without substantial losses from the system (Baillie 1989, Burnham 1989). In such dystrophic systems, organic matter and particularly the forest litter mat may play an essential role in conserving nutrients for sustaining forest produaion (Stark and Jordan 1978). 

Ross, S. M. 1992. Soil and litter nutrient losses in forest clearings close to a forest-savanna boundary on Marac4 island, Roraima, Brazil. Pages 119-143. in P. A. Furley, J Proctor, and J. A. Ratter, editors. Nature and Dynamics of Forest-Savanna Boundaries. Chapman and Hall, London. 

Most of the ecosystem nutrient losses occurred during the plantation establishment phase because of the removal of forest debris at clearing and soil dismrbance during mechanized operations. Despite the potential improvement in Ca levels and maintenance of Mg levels as mentioned for Gmelina, both the extraction of nutrients during harvesting, and leaching losses prior to canopy closure, lead to a depletion of key nutrients, particularly potassium, that must be replaced by fertilization if yields are to be maintained (Sanchez et al. 1985, Russell 1987). 

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