Determination of micro nutrients in substrates by water extraction and interpretation of the analytical data

In 1974 the 1:1½ volume extract was published (Sonneveld et al., 1974) as a water extraction method for the determination of available nutrient elements and of the salinity status of peaty substrates. The analytical data of this extract were related to the data of the “substrate” solution extracted from the substrates with a moisture condition of -3.2 kPa. The method has been widely used and offers a suitable basis for fertilization of peaty substrates. In the years after publication, the composition and application of substrates has undergone much change and the irrigation methods have also been thoroughly adjusted. The latter was responsible for increased water contents in the substrate during crop growth. Therefore, another study was carried out in which the analytical data of the 1:1½ volume extract was compared with the analytical data of the “substrate” solution, where the “substrate” solution was defined at the moisture condition of -1.0 kPa. There was a good agreement between the results of both studies. However, the regression coefficients for the relationships between the data of the extracts differ, as expected, because of the higher moisture contents on which the substrate solution was defined. In addition to the data of major elements published, in the second study, micro nutrients were determined in the extracts, but not published. Therefore in this paper the relationships between the concentrations of micro nutrient as determined in the 1:1½ extract and in the “substrate” solution are given. The relationships presented support the interpretation of analytical data of micro nutrients by means of water extraction

The effects of Fe-chelate type and PH on substrate grown roses

Substrate grown roses appear to be susceptible to chlorosis, which indicates problems with Fe or Mn uptake and hence yield reduction. In common practice this problem is often treated by the addition of extra Fe-chelate, or the use of Fe-EDDHA instead of Fe-DTPA. In previous tests, it was shown that the pH in the root environment is a major factor in the prevention of chlorosis. Moreover, the application of Fe-EDDHA does not always show satisfying improvements in practice. The interaction between Fe-chelate types (EDDHA and DTPA) and pH was studied with roses cv. ‘Kiss’ and ‘Escimo’ on glasswool substrate, reusing drainage water. pH levels compared were about 7, 5.8 and 4.5. The treatments resulted in significant chlorosis and consequently yield reduction at high pH with both cultivars and both chelate types. Highest yields were obtained at low pH, especially with ‘Escimo’. The Fe uptake was clearly affected by the pH with both chelate types. At high pH the Fe-uptake was significantly higher with Fe-EDDHA; however the Mn contents in the plant were significantly lower with these treatments. The uptake of Zn and Cu was also affected by specific combinations of pH and the type of chelate. It was concluded that an optimal pH control was the best method of preventing chlorosis. The choice of the chelate type was less effective and could enhance Mn deficiency

Modelling welfare effects of a liberalisation of the Dutch electricity market

The Dutch electricity sector has traditionally been dominated by the public sector. Although this organisational structure resulted in a reliable and low-priced system, it is said not to be completely stable and efficient. National and international developments stimulate the introduction of a liberalised system. In this article, we present the model NEDMOD which is used to estimate possible welfare gains of an implementation of a liberalised market system in the Dutch electricity market

Nitrogen balances in Dutch organic greenhouse production

The organic greenhouse production in the Netherlands is limited with regard to the number of growers, but plays an important role in EU organic greenhouse production. In the high-technology greenhouses a high production level is realized but nitrogen balances of this production system have been questioned. In order to document and improve the nitrogen balance, the production of seven greenhouses was monitored and soils were repeatedly analysed. The model “Bemestingsrichtlijn biologische kasteelten” (Fertilization Guide Organic Greenhouse Production) has been developed to simulate nitrogen availability and to fine-tune manure applications to crop demand. In the course of four years the overall nitrogen surpluses decreased sharply, but due to the observational character of the research no statistical analyses can be made. Part of the high surpluses in the first years can be explained by initial investments in soil organic matter. Calculation of the dynamic balance gives more possibilities to fine-tune farmers’ fertilization strategies. Growers that followed the model-based advise for manure application, realized a substantial reduction of nitrogen surpluses