Soil phosphorus testing for intensive vegetable cropping

Environmental concerns and rapidly decreasing phosphorus (P) resources caused a renewed interest in improving soil P tests for a more efficient P fertilization. This led to the development of better P fertilizer recommendation systems for major arable crops and grass. Nevertheless, these P fertilizer recommendation systems seem to fail for intensive vegetable crops, with often a very short growing season and limited rooting system. This leads to low P use efficiencies in the horticultural sector. In order to address this problem we set up a study to answer following questions: (1) which soil P test predicts the plant available P content for intensive vegetable crops the best and (2) can new insights, such as combining different soil P tests, improve P fertilizer recommendations for intensive vegetable crops? To this end, bulk samples of 41 soils with very different P status (based on ammonium lactate extractable P) were collected. The plant available P content of these soils was determined using six commonly used soil P tests (P‐CaCl₂, P‐water, P‐Olsen, P‐acetate, P‐lactate, and P‐oxalate) and a P fertilizer pot experiment with endive (a very P sensitive vegetable crop) was conducted. Six pots of each soil were planted with endive. Three of these pots received no P fertilization (0P) and three pots received ammonium polyphosphate equivalent to 24 kg P ha^?1 (24P). All other factors were kept constant. Relative crop yield of the 0P fertilized plants compared to the 24P fertilized plants was determined. Plotting these relative yields against the P status of the soil per soil P test allowed to fit a Mitscherlich curve through the data. Also the combination of two different soil P tests to predict the relative yield with a Mitscherlich equation was evaluated. The coefficients of variation of the soil P tests, the R² values and the relative standard errors of the parameter estimates revealed that P‐acetate and P‐water predicted the relative yield of the 0P plants the best and that combining two different soil P tests gave no extra predictive power. This finding may form the basis for the development of a new P fertilizer recommendation system for intensive vegetable crops, leading to an improved P use efficiency in horticulture. In order to develop this new system more data relating soil P test values with RY of intensive vegetable crops should be collected.     

Temperature related instability of a naturally induced cytoplasmic male sterility in industrial chicory (Cichorium intybus L.)

Natural alloplasmic cytoplasmic male sterile (CMS) clones of industrial chicory were obtained after crossing wild chicory with selected breeding lines. We investigated the CMS stability of 10 clones in various environmental growing conditions. CMS was stable under cool growing conditions in most of them. Fertility restoration, based on pollen production scores, was observed in all clones after a period of hot temperatures. The early flower bud stage was sensitive, resulting in fertile flowers 12–17 days after exposure to high temperatures. Experiments under controlled growing conditions at 15°C demonstrated that a heat shock of 2 days at 25 or 30°C was sufficient to restore fertility. Sterile flowers were formed when plants were again grown at lower temperatures. Significant differences between individual clones were observed, indicating the potential of genetic selection to obtain stable CMS parent lines.     

Quality Criteria for Re-Use of Organotin-Containing Sediments on Land (7 pp)

Background, Aim and Scope   The use of organotin compounds as antifouling agents on ships is prohibited at EU level since 1 July 2003. Because of its persistence, the presence of organotin compounds in harbour sediment will however remain a problem for years. Dumping of dredged sediment in sea is subject to very strict quality criteria, stimulating the exploration of re-use alternatives, such as re-use on land. Within the TBT Clean project (EU LIFE Project 02/ENV/B/341) an assessment framework for re-use of organotin containing treated sediment on land as secondary granular building material was developed. Three scenarios were considered: free re-use on land, re-use above groundwater level with cover layer, and re-use under groundwater level (the latter two scenarios are referred to as restricted re-use). Receptors considered were humans, ecosystem and groundwater. Generic upper concentration limits and sediment leaching limits were calculated. Materials and Methods: Upper concentration limits were calculated with the Vlier-Humaan model. This model allows to calculate soil remediation values according to the Flemish legal framework. The focus of the methodology is the protection of human health, although a check for ecotoxicity was included in the project. The soil remediation value for residential land-use was selected within the scenario for free re-use; for restricted re-use (no direct contact possible), the soil remediation value for industrial land-use was selected. Leaching values were calculated with an analytical soil and groundwater transport model. The reference scenario behind the leaching criteria of the European Landfill Directive was modified to fit the project objectives. Default values for application height and length were used. The point-of-compliance was situated at 20 m distance in the groundwater. Physicochemical properties were taken from literature; sorption characteristics were taken from literature and were measured on 6 treated sediment samples during the project. Plant-uptake values were taken from the literature. Toxicological criteria were taken from EFSA. Results: The assessment framework provided an upper limit (SedUL) and an leaching value (SedLV) for each scenario, expressed as mg/kg dm in the sediment. Criteria were calculated for tributyltin (TBT) and dibutyltin (DBT); too few data were available for monobutyltin (MBT). The SedUL equalled 0.51 mg TBT/kg dm and 0.07 mg DBT/kg dm for free re-use and 195 mg TBT/kg dm and 205 mg DBT/kg dm for restricted re-use (two scenarios). For free re-use the SedLV was only limiting for TBT at Kd of < 2000 l/kg in the sediment. Under re-use above groundwater level with coverage SedLV values ranged from 6.9 – 29 mg TBT/kg dm and from 12 – 33.3 mg DBT/kg dm (Kd ranging from 100 – 10000 l/kg); under re-use below groundwater level SedLV values ranged from 0.007 – 0.77 mg TBT or DBT/kg dm (Kd ranging from 100 – 10000 l/kg). Discussion: Results are subject to large uncertainties because of variation in input data; the model output is sensitive to variation in plant uptake (SedUL for free re-use), Koc or Kd (SedUL for restricted re-use, SedLV for re-use with coverage), Henry's law coefficient (SedUL for restricted re-use); all these parameters show orders of magnitude variation. Conclusions: A feasible and consistent framework for evaluation of the re-use of treated organotin containing sediment was developed. However, the resulting quality criteria are still subject to large uncertainties, due to uncertainties in input data. Recommendations and Perspectives: High-quality data on plant uptake and soil sorption of organotin compounds, the influence of soil properties on these processes, and long-term terrestrial toxicity data are needed to refine the calculations. The quality criteria should be reviewed when these data become available.