Soil Chemical Analysis

Statistics for Spatial Data.

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources. Today, approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale. To meet the world's future food security and sustainability needs, food production must grow substantially while, at the same time, agriculture's environmental footprint must shrink dramatically. Here we analyse solutions to this dilemma, showing that tremendous progress could be made by halting agricultural expansion, closing 'yield gaps' on underperforming lands, increasing cropping efficiency, shifting diets and reducing waste. Together, these strategies could double food production while greatly reducing the environmental impacts of agriculture.

https://escholarship.org/content/qt6xw5g085/qt6xw5g085.pdf?t=ovfwpc

Solutions for a cultivated planet

Changes in Atmospheric Constituents and in Radiative Forcing

As the largest pool of terrestrial organic carbon, soils interact strongly with atmospheric composition, climate, and land cover change. Our capacity to predict and ameliorate the consequences of global change depends in part on a better understanding of the distributions and controls of soil organic carbon (SOC) and how vegetation change may affect SOC distributions with depth. The goals of this paper are (1) to examine the association of SOC content with climate and soil texture at different soil depths; (2) to test the hypothesis that vegetation type, through patterns of allocation, is a dominant control on the vertical distribution of SOC; and (3) to estimate global SOC storage to 3 m, including an analysis of the potential effects of vegetation change on soil carbon storage. We based our analysis on .2700 soil profiles in three global databases supplemented with data for climate, vegetation, and land use. The analysis focused on mineral soil layers. Plant functional types significantly affected the vertical distribution of SOC. The per- centage of SOC in the top 20 cm (relative to the first meter) averaged 33%, 42%, and 50% for shrublands, grasslands, and forests, respectively. In shrublands, the amount of SOC in the second and third meters was 77% of that in the first meter; in forests and grasslands, the totals were 56% and 43%, respectively. Globally, the relative distribution of SOC with depth had a slightly stronger association with vegetation than with climate, but the opposite was true for the absolute amount of SOC. Total SOC content increased with precipitation and clay content and decreased with temperature. The importance of these controls switched with depth, climate dominating in shallow layers and clay content dominating in deeper layers, possibly due to increasing percentages of slowly cycling SOC fractions at depth. To control for the effects of climate on vegetation, we grouped soils within climatic ranges and compared distributions for vegetation types within each range. The percentage of SOC in the top 20 cm relative to the first meter varied from 29% in cold arid shrublands to 57% in cold humid forests and, for a given climate, was always deepest in shrublands, inter- mediate in grasslands, and shallowest in forests ( P , 0.05 in all cases). The effect of vegetation type was more important than the direct effect of precipitation in this analysis. These data suggest that shoot/root allocations combined with vertical root distributions, affect the distribution of SOC with depth. Global SOC storage in the to p3mo fsoil was 2344 Pg C, or 56% more than the 1502 Pg estimated for the first meter (which is similar to the total SOC estimates of 1500-1600 Pg made by other researchers). Global totals for the second and third meters were 491 and 351 Pg C, and the biomes with the most SOC at 1-3 m depth were tropical evergreen forests (158 Pg C) and tropical grasslands/savannas (146 Pg C). Our work suggests that plant functional types, through differences in allocation, help to control SOC distributions with depth in the soil. Our analysis also highlights the potential importance of vegetation change and SOC pools for carbon sequestration strategies.

The vertical distribution of soil organic carbon and its relation to climate and vegetation

https://www.uvm.edu/giee/pubpdfs/Galford_2008_Remote_Sensing_of_Environment.pdf

Wavelet analysis of MODIS time series to detect expansion and intensification of row-crop agriculture in Brazil

https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_53-54/010016060.pdf

Soil properties under Amazon forest and changes due to pasture installation in Rondônia, Brazil

Soil Carbon Sequestration

Tropical soils contain large stocks of carbon and nitrogen that can be altered by clearing for agriculture. In the Brazilian Amazon, cattle pasture is the predominant use for cleared forest lands. We examined changes to soil bulk density and C and N stocks in seven chronosequences, each consisting of an intact forest and pastures of different ages created directly from cleared forest (7 forests, 18 pastures), along a 700-km transect in Rondonia in the southwestern Amazon Basin. The transect included sites with a similar climate but a range of soil types. We used soil δ13C distributions to determine the origin of soil C and to infer changes to soil C cycling patterns after forest clearing. Soil bulk density increased under pasture; these increases were significant in 6 of 18 pastures examined. Changes in C stocks to a depth of 30 cm under pasture ranged from a loss of 0.72 kg/m2 to an increase of 1.77 kg/m2. Soil C stocks increased in 14 of 18 pastures, but these increases were significant in only 4 pastures. Changes in soil N stocks to a depth of 30 cm ranged from a loss of 0.25 kg/m2 to a gain of 0.23 kg/m2 and showed a similar pattern to C, except in one site where we measured significant N loss. Five of 18 pastures accumulated significant amounts of N, and one pasture lost a significant amount of N. Soil δ13C values were greater in pastures than in the original forests, and δ13C values increased with a longer time under C4 pasture vegetation. Bulk density increases were greater on soils with higher clay contents. Carbon accumulation increased with pasture age but was independent of soil texture. Soil C increases to a depth of 30 cm of up to 1.77 kg/m2 amounted to an increase of >50% of the original soil C stock and represented up to 12% of the C in the biomass of forest vegetation. In contrast, changes to soil N stocks in the range of 0.25 kg/m2 approximately equaled the N stock in the original forest vegetation. Our results indicated that when site history was controlled by considering only pastures formed directly from cleared forest, C and N accumulation was the dominant trend in pasture soils. Absence of a correlation between C and N accumulation and soil texture suggested that site history and management may be more important than soil type as determinants of the direction and magnitude of changes in soil C and N stocks.

Carlos Clemente Cerri

Papers

Wavelet analysis of MODIS time series to detect expansion and intensification of row-crop agriculture in Brazil

Soil properties under Amazon forest and changes due to pasture installation in Rondônia, Brazil

Soil Carbon Sequestration

Soil carbon and nitrogen stocks following forest clearing for pasture in the southwestern Brazilian Amazon

The use of stable carbon isotopes for estimating soil organic matter turnover rates