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Application of biochar under wet moisture condition did not impact coconut seedling growth.Under dry moisture BC-Gly enhanced crop growth similar to wet treatments and plant P uptake.AMF growth was not impacted by biochar amendment aside from a stimulation in dry soil by BC-Gly.The N rich BC-Gly likely provides N to the plants via fungi stimulated biochar decomposition.

Soil pore network effects on organic matter turnover have, until now, been studied indirectly because of lack of data on the 3D structure of the pore network. Application of X-ray computed tomography (X-ray CT) to quantify the distribution of pore neck size and related pore sizes from undisturbed soil cores, with simultaneous assessment of carbon (C) mineralisation, could establish a relationship between soil organic matter (SOM) decomposition and soil pore volumes. Eighteen miniature soil cores (diameter 1.2cm, height 1.2cm) covering a range of bulk densities were incubated at 20°C for 35 days. Respiration was modelled with a parallel first- and zero-order kinetic model. The cores were scanned at 9.44µm resolution using an X-ray CT scanner developed in-house. Correlation analysis between the slow pool C mineralisation rate, ks, and pore volume per pore neck class yielded significant (P<0.05) positive correlations: r=0.572, 0.598, and 0.516 for the 150–250, 250–350, and >350µm pore neck classes, respectively. Because larger pores are most probably mainly air-filled, a positive relation with ks was ascribed to enhanced aeration of smaller pores surrounding large pores. The weak and insignificant relationship between the smallest pore neck class (<9.44µm) and ks could be explained by obstructed microbial activity and mobility or diffusion of exo-enzymes and hydrolysis products as a result of limited oxygen availability. This study supports the hypothesis that the impact of soil structure on microbial processes occurs primarily via its determination of soil water distribution, which is possibly the main driver for the location of C mineralisation in the soil matrix.

Intensive vegetable production systems throughout South East Asia are characterised by large nutrient inputs and low nitrogen (N) use efficiencies. In Indonesia, intensive vegetable production is concentrated on volcanic highland soils starting from an altitude of around 700m above sea level. We measured potential N mineralisation from soil organic matter and from several representative organic materials in Andisols and Inceptisols with andic properties from Central Java, Indonesia. Unamended soils and soils amended with crop residues, animal manures, and compost were incubated during 3–4 months at 25°C in the laboratory, then we monitored N mineralisation. Relative N mineralisation was significantly smaller in the Andisols (average 3.6±1.0%) than the Inceptisols (7.4±2.9%), and was negatively related to oxalate-extractable aluminium (Alox) (r=–0.749) and soil organic carbon (r=–0.705). This is probably due to the strong protection of organic matter (and organic N) by binding to active Al compounds. Net N mineralisation from the added organic materials was highly variable (ranging from 68.1% for the broccoli residues to 2.6% for tithonia compost), and was best related to the organic N content (r=0.476). There were no significant correlations between net N mineralisation and biochemical fractions, which we attribute to the large variety of materials used in this study compared with previous studies. The data generated here on N mineralisation potential from soil organic matter, and from a variety of plant materials and animal manures that are commonly used in these intensive vegetable rotations, will allow for the rapid and efficient introduction of N fertiliser advice systems based on balance sheets.

Sandy cropland soils in NW Europe were found to contain unusually high organiccarbon OC levels, and a link with their landuse history has been suggested. This studys aim was to assess the discriminating power of physical and chemical fractionation procedures to yield information on soilorganicmatter OM stability for these soils. In relict and cultivatedheathland soils, much higher proportions of 6 NaOCl treatment–resistant but 10 HF–soluble OC MOC and N 32.2 and 29.9 were measured compared to a set of “permanent"cropland soils without a history of heathland land use 11.9 and 8.5. Also, the proportions of 6 NaOCl– and 10 HF treatment–resistant OC and N in the relict and cultivated heathlands 19.2 and 12.0 were higher than in the permanentcropland soils 17.7 and 5.7. Stepwise multiple linearregression yielded a significant relationship between the annual mineralization g C 100 g OC–1, soil OC g C kg–1 content, and MOC: Annual mineralization = 4.347 – 0.087 soil OC – 0.032 MOC R2= 0.65. Combinations of incubation experiments for quantification of the labile soil OM pool with chemical fractionation may thus yield meaningful data for development of soilorganicmatter models with measurable pools, but their applicability will be limited to specific combinations of former land use with soil, climate, and current management.

Reduced tillage (RT) management may increase surface soil organic carbon (SOC) and nitrogen (N), particularly due to accumulation of labile organic matter (OM). We investigated the effect of RT compared with conventional tillage (CT) on the distribution of SOC and N over different soil fractions from 7 pairs of fields with cereal–root crop rotations, in the Belgian loess belt. Surface soil samples (0–100mm) were physically fractionated according to a sequential sieving and density separation method into stable microaggregates, silt and clay, and free and occluded particulate OM fractions. RT management was previously found effective in increasing the organic C and organic N content of the surface soil (0–100mm) at these 7 sites. Here, physical fractionation showed that the difference in amount of organic C and N in free particulate OM (fPOM), intra-microaggregate particulate OM (iPOM), and silt and clay associated OM between the RT and CT soils contributed 34, 29, and 37% of the increase in SOC and 35, 32, and 33% of the increase in N. The contribution of OC and N in iPOM and fPOM increased significantly on a relative basis under RT management. Only a modest increase in iPOM and slight enhancement of microaggregation was observed in RT compared with CT soils. We suggest that the repeated disturbance of soil by harvest of root crops and repeated use of cultivators and harrows may limit the accumulation of physically protected POM under RT management of these Western European cereal–root crop rotations. Instead, most of the accumulated OC and N in the surface horizons under RT management is present as free unprotected POM, which could be prone to rapid loss after (temporary) abandonment of RT management.

Total soil organiccarbon SOC stocks for grassland soils in Flanders N Belgium were determined for the Kyoto Protocol reference year 1990 and 2000 in order to investigate whether these soils have been CO2sinks or sources during that period. The stocks were calculated by means of detailed SOC datasets, which were available at the community scale for the whole of Flanders. The total SOC stocks for Flemish grassland soils 1 m depth were estimated at 38 Mt SOC in 1990 and 34 Mt SOC in 2000. The loss of SOC resulted from a decrease in the SOC content of grassland soils 71 and could also partly 29 be explained by a decline in grassland area. Significant decreases in SOC for the 0–6 cm depth layer were found for the 1990s for the coarsertextured soils with SOC losses ranging between –0.3 and –0.5 over the 10 y period. Specific management practices that disturb the SOC balance such as conversion to temporary grassland and a reduction of animalmanure application are hypothesized to have contributed to the observed loss of SOC stocks. We furthermore conducted an analysis of uncertainty of the 1990 and 2000 grassland SOC–stocks calculation using Monte Carlo analysis. Probabilitydistribution functions were determined for each of the inputs of the SOCstock calculation, enabling us to assess the uncertainty on the 1990 and 2000 SOC stocks. The frequency distributions of these simulated stocks both closely approached lognormal distributions, and their 95confidence intervals ranged between 150 and 50 of the calculated mean SOC stock. The standard error on the measured decrease in SOC stocks in Flemish grassland soils during the 1990s was calculated to be 7–8 Tg SOC, which is equivalent to twice this decrease. This clearly shows that largescale changes in SOC stocks are uncertaintyridden, even when they are based on detailed datasets.

We examined the effects of 10 yr of reduced tillage (RT) management, compared with conventional tillage (CT), on the chemical composition of soil organic matter (SOM) using a combination of physical fractionation and pyrolysis–field ionization mass spectroscopy (Py–FIMS). Surface soil samples (0–10 cm), which were collected from two adjacent CT and RT managed fields, were separated into particulate organic matter (POM) fractions and sand, silt, and clay size separates. Higher amounts of C (77%) and N (64%) were observed in all size separates of the RT soil and, in particular, the proportion of intramicroaggregate POM was two times as large as in the CT soil. The Py–FIMS spectra showed that larger proportions of free fatty acids, sterols, and N‐containing compounds were present in the RT soil's sand fraction than in the CT soil. Similar observations were also made for both free and intramicroaggregate POM fractions. In the silt and clay size fractions, no substantial differences in SOM composition were measured between tillage treatments, except that the RT soil's clay fraction had a higher proportion of N‐containing compounds and a lower proportion of alkylaromatics. Ratios of carbohydrate hexose to pentose subunits and of lignin monomers + phenols to lignin dimers confirmed a less decomposed character of the SOM in the silt and clay size fractions of the RT soil. These observations can be logically linked to the reduced mixing of crop residues and manure in the soil profile and higher surface soil microbial biomass under RT.

ABSTRACTOrganic farming is put forward as a sustainable alternative to the conventional way of farming. However, until now there has been practically no research on soil related aspects of organic farming in Flanders. Therefore, in this study, the carbon, nitrogen, sulphur and phosphorus status of the fields on organic farms was measured and was related to characteristics of the farms involved (land use, soil texture, management intensity and time since conversion to organic farming) and was, where possible, compared with the general soil fertility status of agricultural soils in Flanders. The SOC (soil organic carbon) contents tended to be larger in the fields of the organic farms studied than in conventional farming. This content was correlated positively with the management intensity of the fields. However, some of the organic fields still had rather low SOC contents. To increase this content organic farmers will need to apply more organic materials with large C:N and C:P ratios taking into account the strict current manure legislation. The mineral N contents on the organic farms measured in the period between 1 October 2003 and 15 November 2003, indicating the risk of nitrate leaching, were well below the average values of the different land use classes of conventional agricultural soils in East Flanders. The available P content of the organic fields was high to very high as is also the case for conventional agriculture in East Flanders and was strongly related to the management intensity.

We have studied the short term C mineralization of six wastes from important food industries, one sludge from a biogas plant and three composts. All the wastes were characterized chemically and fractionated according to the Van Soest method. The fresh wastes were incubated under controlled environment conditions to determine the C mineralization rate. Based on first order mineralization kinetics, we calculated the hypothetical amount of stable C in the wastes as the amount of C that would not be mineralized within one year under field conditions. The percentage of stable organic C in the organic matter was in general much larger in the composts than in the other wastes, but when expressed on dry matter, the non-composted wastes had comparable or larger amounts of stable organic C than the composts and have a considerable potential for supplying organic matter to soils, and hence for C sequestration. The amount of stable organic C could best be predicted by the total N content of the wastes (Ra2= 0.855), whereas the results of the fractionation had very little predictive power, probably due to problems related to the high ash content of some of the wastes. An index that combined stable organic C and N and P content in the wastes was calculated to assess possible limitations for applying these wastes in agriculture. Under current nutrient legislation in Western Europe, a number of these wastes will only be usable in small amounts, but these and other food industry wastes could still prove to be valuable soil amendments in nutrient poor situations, for increasing soil organic C content and supplying nutrients.