Amelioration of Composts for Greenhouse Vegetable Plants Using Pasteurised Agaricus Mushroom Substrate

When using food and green waste composts as peat-free plant growing media, there is a challenge that nutrient immobilisation and high pH and salts content limit plant growth. The present study explored the use of spent mushroom compost (SMC) of Agaricus subrufescens in a sustainable plant growing system where only vermicompost from digested food waste and composted green wastes were used, even for the seedling stage. However, negative effects of high compost inclusion were offset by adding SMC. Significantly higher plant yield was obtained in several of the SMC amended treatments in four out of five lettuce experiments and in one tomato experiment. In addition, an experiment with cucumbers showed that nutrients were not available to the plant when the mushroom mycelium was actively growing, but became available if the mushroom mycelium had been inactivated first by pasteurisation. A significant effect from SMC was not observed under full fertigation. This study demonstrated that the addition of pasteurised Agaricus mycelium colonised compost can successfully offset negative effects from high pH and EC as well as limited nutrient supply (and nitrogen immobilisation) in peat-free, compost-based growing media.

An interpretative model of carbon and nitrogentransformations applied to a residue incubation experiment

A simple model of 3 equations was devised to simulate the rates through time of gross mineralisation of nitrogen, nitrogen immobilisation, and microbial respiration relating to individual inputs into soil of plant residues of any age or type. Using published data from an incubation experiment carried out in Iowa, we applied the model to a residue newly added to soil, to the original soil organic matter (SOM), and to a mixture of these. Manipulation of the model allowed the derivation from the Iowa data of a net mineralisation index which seemed to summarise the nitrogen release characteristics of the residue in all treatments of the experiment. The equations and parameter values developed for the added residue were applied to SOM using results from unamended soil. The balance between respiration and mineralisation was found not to correspond to that expected for old organic matter near an equilibrium carbon/nitrogen ratio. Rate constants of mineralisation and respiration for SOM were adapted to overcome this apparent anomaly. To model the dynamics SOM and added residue simultaneously, the 2 sets of 3 equations were applied in parallel to 4 extreme treatments in the with-residue series (lowest and highest nitrate levels with low and high residue additions). To achieve the fits presented, only 2 of the 12 parameters required in each set of equations needed to differ between the set for SOM and that for added residue. The model reproduces well most of the primary Iowa data and also some derived results. Use of the model helped to interpret divergences between simulations and data.

Modelling Nitrate Output from Agricultural Watersheds Using a Hydrological Model

A distributed area model called CEQNIT (CEQUEAU-NITRATE) to predict nitrate concentration and load from agricultural watersheds has been developed. The model application requires that the watershed be divided into partial squares. At partial-square scale, the model simulates nitrogen reactions within the soil and nitrate leaching. Nitrogen budget in the CEQNIT model includes the leaching of nitrate, plant uptake, denitrification, mineralization of organic nitrogen, immobilisation, nitrification, input by fertilizer and precipitation. Nitrogen dynamics were simulated as first-order kinetic reactions, and the influence of soil temperature and moisture were included. The model requires input from the CEQUEAU hydrological model that provides temporal and spatial estimation of flow discharge over the watershed. Using two-year data from a small agricultural watershed (78 ha), the model was calibrated with first-year data and tested with the second-year data. Results obtained from this study showed that the model was able to reproduce the seasonal nitrate fluctuations accurately.