Soil organic matter

Reforestation with trees and shrubs may be an effective means of increasing soil organic matter content and for regeneration of degraded lands. A study was conducted on a degraded farmland Chromic Luvisol (UNESCO/FAO) or Udic Rhodustalf (USDA, 1999) in the moist semi decidu-ous zone of West Africa, near Onwe, located at latitude 06o 41 ’ N, longitude 01o 28 ’ W, and at an altitude of 305m asl. The objective of the study was to quantify the improvement in soil physico-chemical properties of degraded Chromic Luvisol with exotic leguminous tree species compared to grass vegetation in the moist semi-deciduous zone of West Africa. To quantify changes due to reforestation, we measured some physical and chemical properties of soil after 20 years (1989 – 2009) of reforestation with Acacia angustissima (Acacia), Cassia siamea (Cassia), and Leucaena leucocephala (Leucaena) mixed and compared with soils under natural grass vegetation. Experi-mental design used for soil sampling and for evaluat...

The reports map the flow of carbon through the Swedish Food and Agriculture System, all the way from net primary productivity to human waste and sewage. Animal feed and metabolism, food industries, import and exports, losses etc are all included.

There is considerable concern in Europe that soil organic matter (SOM) contents are declining, which would threaten both agriculture and the environment. We performed a trend analysis of SOM contents in sandy soils, using historic data from routine agricultural soil analyses. Data were selected from grass, grass-maize rotation and maize fields in four adjacent provinces that had been sampled four to five times during the period 1984–2004. Absolute (at least 1%) and relative changes (SOMt=20/SOMt=0) were calculated and regressed against initial SOM contents. Mean SOM content showed a north-south gradient per cropping system. We found no single uniform trend in SOM contents for any of the three systems. Over the 20-year period, SOM declined in c. 25% of all grasslands, amounting to 185 000 of the 635 000 hectares of land under grass and forage crops in the four provinces, and increased in a total of 267 000 hectares. Carbon accumulation in grassland sandy soils was calculated at 39 g C m−2 year−1 (top 5 cm). For the grasslands, initial SOM contents were linearly and negatively related to absolute changes in SOM; the relation with the relative change was best explained by using log-transformed values of SOM. We conclude that in grassland soils in the Netherlands, conservation of SOM requires identification of high-risk fields rather than high-risk areas. For continuous maize on sandy soils, the entire area may be denoted as high-risk, because all fields could reach the critical limit of 3.4% SOM in the near future.

To detect soil changes related to vegetation and fertility restoration in a long fallow agricultural system of the Venezuelan Andes, 32 soil (A horizon, 0–15cm depth) and litter characteristics were studied in plots at different stages of the fallow-cultivation cycle. Four sectors of the valley were sampled, each one including seven plots: recently ploughed after a long fallow period; 1

Long-term changes in soil organic carbon (SOC) resulting from management change are documented for many experimental situations, and corresponding trends in the field have been observed by national survey. Since these changes are relevant to atmospheric carbon balance a practical measure to confirm the impact of recent management decisions at any location, without resorting to repeated sampling, is highly attractive but none has previously been tested. This study assessed intra-aggregate C to fulfil the role, based on a temporary deviation from its predictable contribution to total SOC under stable management. A total of 166 surface soil samples (0–15 cm) were analyzed for intra-aggregate C using an established physical fractionation protocol or compatible scaled-up procedure. Soils were arable (or ley-arable) managed by conventional or minimum-tillage, or permanent grassland, and assigned ‘stable’ or ‘changing’ status on the basis of a verbal account of management history. Log-normal populations of intra-aggregate C were compared for soils of stable and changing status using F-tests. Intra-aggregate C shows promise as an indicator of changing SOC in arable soils up to 30% clay content, particularly soils <20% clay. A larger dataset is required to establish its utility in grassland soils. It is not certain that intra-aggregate C is capable of confirming direction of change or trajectory (endpoint), and functions to indicate change, rather than confirm stable status. Supplementary information on the history of soil use and management is therefore essential in the interpretation of such measurements.

Tbe potential for using coal-derived humic substances to improve the available water holding capacity (AWC) and awegate stability of typical Mediterranean soils was evaluated in the laboratory using an agricultural surface (0-20 cm) soil from each of three regions of Ital}, (Sicil}, Tuscany and Venetia) and five rates of humic acids (HA), 0, 0.05, 0.10, 0.50 and 1.00 g/kg.There were significant (P < 0.05) differences between the field capacity (FC), permanent wilting point (PWP), and availablewatercapacity(AWC) values of the controls and those treated with 0.05 glkg of the HA. Beyond this rate, differences in these pr[)perties were not significant. At the 1.00 g/kg HA rate, the relati,'e improvements in AWe over the three controls were 30%, 10% and 26%. Low rates (0.05 to 0.10 g/kg) of HA were also needed to obtain a 40 to 120% improvement in aggregate stability of these soils relative to the controls. These results indicate that the addition of highly humified organic matter such as coal-derived humic substances can improve the structural and water retention properties of degraded arable soils. However, since there is not yet any direct evidence that these humic materials can ameliorate soils under field conditions, field studies will be needed to validate these results.

Earthworm casts, formed when organic substrates and soil minerals pass through the digestive tract, may protect soil organic matter from biological degradation if they persist in the soil. Yet, the stability of casts is affected by their location in the soil profile because surface casts are exposed to more disruptive forces (wetting-drying, freezing-thawing) than subsurface casts. It is not known