Jean Vanderdeelen

Phosphate enrichment in the sandy loam soils of West-Flanders, Belgium

The last three decades, pig breeding has evolved towards a specialised, large scaled, land independent bio-industry in the province of West-Flanders. Subsequently, in certain regions, very high amounts of liquid pig manure are produced each year. This pig slurry is used as a fertilizer at a rate which very often exceeds normal agricultural practices. Because of the nonequilibrium between the phosphorus crop requirements and the P-inputs, phosphates accumulate in the soil. However, the phosphate sorption capacity of a soil is limited. Once the sorption capacity is exceeded, phosphates will start leaching through the soil profile. Since, during winter, in these areas, the groundwater table is situated at a depth of less than 1.0 m, phosphate breakthrough might take place. In the sandy loam soil region (± 1000 km2) of the province, an inventory of the P status of the soil was made. The region was sampled according to a regular grid with 2 km intervals. At random, some sample points were only 500 m apart. This resulted in a total of 296 samplings. In view of fertilizer recommendations, lactate extractable P of the plough layer (0–30 cm) was determined. A maximum value of 101 mg P 100 g-1 of air dry soil, a minimum value of 6 mg P 100 g-1 and a median value of 31 mg P 100 g-1 were found, indicating that for half of the spots monitored, the P status of the soil is high to very high. An oxalate extraction was done to investigate the phosphate saturation of the soil profile (0–90 cm). Based on a critical phosphate saturation degree of 30%, more than half of the soil profiles are phosphate saturated. Phosphate leaching at a rate higher than 0.1 mg ortho-P l-1 at a depth of 90 cm can be expected. Therefore, a restriction of the P fertilization should be highly recommended. The geostatistical processing of the data using block kriging resulted in a spatial continuous estimate of the phosphate saturation degree. A good agreement was found between the pig density and the phosphate saturation degree of the soil profile.

Effect of soil properties on the kinetics of phosphate release

Abstract The kinetics of the phosphate release by 35 non‐calcareous soil samples were investigated by consecutive extraction of the soil. The soil samples covered a wide range of texture, pH and degree of phosphate saturation. For all soils, phosphate release initially followed first order kinetics. With time, the process became linear to the logarithm of time. These relationships were used to distinguish between the initial fast process of phosphate desorption and the much slower diffusion‐dissolution process. The influence of physico‐chemical soil properties on the parameters describing the two processes was investigated using multiple regression analysis. The total amount of reversibly adsorbed phosphate was highly significant correlated to the oxalate extractable phosphate of the soil: the former approximated 33 % of the latter. The rate constant of the initial desorption process was mainly influenced by the pH of the soil: increasing the pH positively affects the desorption rate. The kinetics of the ...

Catalytic durability of magnetoproteoliposomes captured by high-gradient magnetic forces in a miniature fixed-bed reactor.

Cytochrome c‐oxidase, used as a model membrane‐bound enzyme, was embedded in phospholipid bilayer membranes, attached to nanometer‐sized Fe3O4 colloids (so‐called magnetoliposomes). In comparison with the lipid‐depleted free enzyme, both the activity and the enzymatic stability of the complexes, stored at 4°C, were considerably enhanced. These beneficial properties of magnetoproteoliposomes have been successfully exploited in a magnetically controlled fixed‐bed bioreactor, operating in a continuous flow regime.

Variability of the phosphate saturation degree of the sandy loam soils in west‐flanders, Belgium

The variability of the phosphate sorption capacity (PSC) and the phosphate saturation degree (PSD) of the soil profile was studied in the sandy loam soil region (+/-1000 km(2)) of West-Flanders at different scales. In the frame of a regional inventory, the soil profile was sampled at 2000 m intervals on a square grid. In total, 296 observations were made. Additionally, in this area, 21 fields were sampled in detail: 15 augerings per field were made. Finally, on one field, seven observations were made at the micro scale: five augerings within a circular area of 30 m(2). All soil samples were analyzed for ammoniumoxalate extractable Fe, Al and P and the PSC and the PSD were calculated. The coefficient of variation (CV) of the PSC of the whole soil profile 0-90 cm was found to be 7% on the micro scale, 20% on the field scale and 28% on the regional scale. The CV of the PSD was found to be 9%, 21%, and 48% respectively. This means already quite a proportion? about 20%, in variation in PSC and PSD is situated at short distances (< 5m) Most of the variability in PSC is already found at the field level. On the contrary, the CV of the PSD is twice as high on the regional scale compared to the field scale. This may be explained by the regional structure of the P inputs, due to the local intensification of pig breeding activities. The criterion phosphate saturation is stochastically approached at the field scale. In the study area, the mean field averaged CV of the PSD was 21%. Taking into account the uncertainty when sampling, supposing a lognormal distribution of the PSD, the critical PSD of 24% is translated into a practical threshold PSD of 26% if 15 measurements per field are taken and a probability of 95% is pursued.

Phosphorus uptake by Kallar grass [Leptochloa fusca (L.) Kunth] from different depths in saline and non-saline soil

Abstract The uptake of 32 P by roots of Kallar grass [ Leptochloa fusca (L.) Kunth] to assess P uptake from different depths was investigated in two soils differing in salinity. The isotope was introduced at three depths (5, 15 and 25 cm) in the profile and uptake was assessed by 32 P recovery in the herbage on two successive harvests (II and III) after the initial establishment period (harvest I). At harvest I, biomass yield of Kallar grass was lower in the saline soil than in the normal soil. It is shown that this crop has a relatively low tolerance to saline conditions at the seedling stage and that tolerance increases during subsequent growth. P concentrations in shoots were similar in plants from saline and normal soil at harvests I and II but markedly higher for the saline soil at harvest III. Root P concentrations were also higher in plants grown in the saline soil than in those in the nonsaline soil. At harvest II, the uptake of 32 P by roots of Kallar grass decreased significantly with depth in the saline soil, while it was greater in the 20–35 cm zone than in the upper profile at harvest III. In normal soil, 32 P uptake was significantly greater in the upper 20 cm zone than the lower depth at harvest II, but it was similar throughout the profile at harvest III. The results indicate that Kallar grass is capable of maintaining P uptake under salinity stress. The species may extract substantial amounts of nutrients from deeper soil horizons and thus can thrive on low-fertility saline soils.

GROWTH AND PHOSPHORUS UPTAKE OF ATRIPLEX-AMNICOLA AT DIFFERENT LEVELS OF NACL.

Growthof Atriplex amnicola P.G. Wilson was not affected by different levels (10, 100, and 200 mM) of NaCI. Na concentrations in roots and shoots increased significantly at higher levels of NaCI. K/Na ratios in plant parts were higher compared to those in the external solutions, indicating selectivity for K over Na. P uptake, as determined using32P, was not affected by increasing NaCl in the root medium.