Biochar effect on the mineralization of soil organic matter

The objective of this work was to verify whether the addition of biochar to the soil affects the degradation of litter and of soil organic matter (SOM). In order to investigate the effect of biochar on the mineralization of barley straw, soil was incubated with 14C-labelled barley straw with or without unlabelled biochar. To investigate the effect of straw on the mineralization of biochar, soil was incubated with 14C-labelled biochar with or without straw. In addition, to investigate the effect of biochar on old SOM, a soil labelled by applying labelled straw 40 years ago was incubated with different levels of biochar. All experiments had a control treatment, without any soil amendment. The effect of biochar on the straw mineralization was small and nonsignificant. Without biochar, 48±0.2% of the straw carbon was mineralized within the 451 days of the experiment. In comparison, 45±1.6% of C was mineralized after biochar addition of 1.5 g kg-1. In the SOM-labelled soil, the organic matter mineralized more slowly with the increasing doses of biochar. Biochar addition at 7.7 g kg-1 reduced SOM mineralization from 6.6 to 6.3%, during the experimental period. The addition of 15.5 g kg-1 of biochar reduced the mineralized SOM to 5.7%. There is no evidence of increased degradation of either litter or SOM due to biochar addition; consequently, there is no evidence of decreased stability of SOM

Below-ground competition between trees and grasses may overwhelm the facilitative effects of hydraulic lift

Contains fulltext : 60125.pdf (publisher's version ) (Closed access)Under large East African Acacia trees, which were known to show hydraulic lift, we experimentally tested whether tree roots facilitate grass production or compete with grasses for below-ground resources. Prevention of tree-grass interactions through root trenching led to increased soil water content indicating that trees took up more water from the topsoil than they exuded via hydraulic lift. Biomass was higher in trenched plots compared to controls probably because of reduced competition for water. Stable isotope analyses of plant and source water showed that grasses which competed with trees used a greater proportion of deep water compared with grasses in trenched plots. Grasses therefore used hydraulically lifted water provided by trees, or took up deep soil water directly by growing deeper roots when competition with trees occurred. We conclude that any facilitative effect of hydraulic lift for neighbouring species may easily be overwhelmed by water competition in (semi-) arid regions

Mechanisms of Soil Aggregates Stability in Purple Paddy Soil under Conservation Tillage of Sichuan Basin, China

Part 1: Decision Support Systems, Intelligent Systems and Artificial Intelligence ApplicationsInternational audienceRidge culture is a special conservation tillage method, but the long-term influence of this tillage system on soil aggregate-size stability in paddy fields is largely unknown in southwest of china. The objectives of this paper are to evaluate soil aggregates stability and to determine the relationship between SOC and soil aggregate stability. Soil samples at 0-20 cm layer were adopted from a long-term (16 yr) field experiment including conventional tillage: plain culture, summer rice crop and winter upland crop under drained conditions (PUR-r), and conservation tillage: ridge culture without tillage, summer rice and winter fallow with floodwater layer annually (NTR-f), and winter upland crop under drained conditions (NTR-r), and wide ridge culture without tillage, summer rice crop and winter upland crop under conditions (NTRw-r), respectively. The determination of aggregate-size stability distribution involves the assumptions that soil aggregates can be categorized in terms of their size and water stability (slaking resistance). Experimentally this procedure involves the slaked and capillary-wetted pretreatments; and a subsequent slaking treatment of aggregates >0.250 mm in size. WSMA and NMWD were applied to simulate the breakdown mechanisms of aggregates for studying soil stability based on aggregate resistance to slaking in paddy soil. The results showed that the amount of aggregates-size was greatly observed in the fraction of 2~6.72 mm under ridge culture in paddy soil (more than 50%) under slaking and capillary-wetting pretreatment. The proportion of soil macro-aggregates (>0.25 mm) in conservation tillage was greatly higher than that in conventional tillage under subsequent slaking treatment. Minimal differences of aggregate stability between slaking and wetting were observed, while significant differences were found between ridge culture and plain culture. The aggregates stability under slaking treatment ranked in the order of NTR-r>NTRw-r>NTR-f>PUR-r, while under wetting was NTRw-r>NTR-r>NTR-f>PUR-r, respectively. There was a positive correlation between the aggregates stability and SOC concentrations under wetting, and low correlation was observed under slaking pretreatment. Soil exposure with tillage and lack of rice/rape-seed stubble inputs caused declines in aggregation and organic carbon, both of which make soil susceptible to water erosion. Adoption of ridge culture with no-tillage integrated with crop rotation and stubble mulch significantly alter soil organic concentration, suggesting it was a valuable conservation practice for soil aggregation and soil organic carbon sequestration on paddy soil