Soil structure
“Best bet” Land-use Systems
Country reports
Alternatives to Slash-and-Burn in Brazil
Agronomic Sustainability
Unique id: IDAUBSCE
Source file: D:\Projects\ASB\ASB Country and Thematic reports\Brazil country report\ASB Brazil Summary Report.xml
Authors: S. Vosti, C. L. Carpentier, J. Witcover, . Carvalho dos Santos, E. Muñoz Braz, J. Ferreira Valentim, S. J. de Magalhães de Oliveira, C. Palm, F. de Souza Moreira, A. Cattaneo, A. Gillison, A. Mansur Mendes, V. Rodrigues, T. C. de Araújo Gomes, M. V. Neves d’Oliveira, E. do Amaral, S. Fujisaka, C. Castilla, T. Tomich, D. Bignell, D. Gonçalves Cordeiro, A. Hermes Vieira, R.S. Correira da Costa, M. Faminow, M. Locatelli, M. Swift, S. Weise, M. van Noordwijk, N. Sampaio, I. L. Franke, H. J. Borges de Araujo, L. M. Rossi, E. Barros, B. Feigl, S.P. Huang, J. Cares, C. Pinho de Sá, . Carneiro, P. Woomer
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Good soil structure is critical for maintaining the
long-term capacity of agricultural land to produce crops. Soil compaction(as
indicated by bulk density), soil carbon and soil carbon saturation deficit (a
measure of the decline in soil organic matter relative to a calculated
reference) are key to maintaining soil structure. A calculation for reference
carbon was developed based on an equation using soil texture and pH values (at
0-15 cm soil depth) calibrated against soils in
Reference carbon (refC) = exp (1.333 + 0.00994*Clay % + 0.00699*Silt % - 0.156*pH);
orgC = organic carbon in soil as measured by soil analysis;
relative carbon (relC) = (orgC / refC);
carbon saturation deficit (defC) = 1 – relC.
The values for non-forested land uses are then compared with those for forest, which was used as the reference LUS.
Adequate soil cover is important for protecting the soil against the direct impact of raindrops and full sunlight. Longer and more frequent periods of soil exposure can lead to the deterioration of soil structure. Several indicators for this were developed:
Soil exposure = ratio of the number of months of low soil cover the length of the LUS
(in months);
Note: low soil cover = dichotomous indicator: 1 = the canopy of all strata of vegetation plus any litter provide soil cover of less than 75-80% (it is assumed that all crop/plant species and litter are distributed in a regular pattern across the farmer’s field and that the soil surface is adequately protected with greater than 75-80% soil cover).
An indicator was developed for assessing the frequency of removal of a protective canopy cover:
Open time = number of years since the land was last cleared, or the interval in years between clearings.
The soil cover index integrates the information on both soil exposure and open time into a single indicator:
Soil cover index = length of system cycle (in months), less soil exposure time (in months).