Effect of Controlled-Release Fertilizers on Chemical Parameters of Two Growing Media during 12 Months Storage

A one year long incubation experiment was carried out using a peat-based growing media (GM) and a peat and pumice GM (80% and 20% v/v), in combination with two controlled-release fertilizers (CRFs) and stored in two conditions. Samples with 60% water content were kept at 21\ub0C throughout the experiment (correct storage condition) or at 40\ub0C for 15 days and then at 21\ub0C until the end of the experiment (improper storage condition). Three replicates of each treatment were analyzed monthly for pH, EC, water soluble potassium, phosphorus and mineral N (1:5 vol/vol extraction method). The strong acidification induced by CRFs reduced pH of the peat based growing media below the permitted tolerance of pH (\ub1 1 unit of the declared value) after 60 days, and peat-pumice GM after 30 days correct storage. Soluble salts buildup during two month storage led both GM to exceed admitted tolerance (25% of the declared value) for Italy. Biological oxidation of ammonium was more efficient in the most aerated substrate (peat-pumice GM) based on measured ammonium versus nitrate in the soil solution. Potassium concentrations were lower in peat-pumice based GM for possible interaction between potassium and pumice. No changes in phosphorus extracted by water were detected. The intensity and pattern of nutrient release from CRFs were influenced both by storage conditions and by GM type. During the first 3 months of incubation improper storage increased ammonium build up in both GM

Behaviour of hoof and horn during the storage of peat-based and peat/pumice-based growing media

Hoof and horn is one of the most widely used organic fertilizers by the Italian substrate manufacturers and it is frequently used for substrates devoted to organic production. Together with chemical fertilizers, it is used for long lasting conventional production. A recent national law (Leg. Decree n.75, 2010) set up a series of rules in substrate production and set tolerance degrees for pH and EC. At present there is little information regarding the influence of organic fertilizers on pH and electrical conductivity (EC) during the storage of growing media. An experiment has been carried out in order to investigate the behaviour of hoof and horn added to two growing media (a peat based media and a mixture of peat 80% and pumice 20% v/v). These media were stored for 12 months at a constant temperature of 21\ub0C or kept at 40\ub0C for 15 days and then at 21\ub0C until the end of the trials. In all treatments pH decreased exceeding dramatically the degree of tolerance. The more aerated substrate promoted the fastest and widest pH reduction. The heat treatment reduced the acidification of media maintaining the final pH slightly higher than in samples non heated. The substrate containing pumice induced an early increase in EC values while both the heated media showed the highest differences between initials and final values. In both growing media EC values exceeded the admitted tolerance. Results showed a dramatic effect of temperature treatment and marked differences between the studied growing media

Evaluation of almond shells as cover material and minor component of substrates for young plants

Almond trees are grown in southern Italy, mainly in Sicily and Apulia. It is estimated that every year no less than 100,000 m3 of almond shells (AS), the ligneous material forming the thick endocarp or husk of almond fruit, incur as byproduct which is mainly used for domestic or greenhouse heating. Sometimes almond shells are used in mixtures with other organic materials to prepare green compost. This study investigates the physical and chemical features of crushed AS and their behavior when used in vegetable nurseries. High air content, low shrinkage, low water retention, moderate swelling capacity, low EC, sub-acid pH and an appreciable lignin content are some of the observed peculiarities. Trials were carried out using a granulometry fraction of 1-2 mm, in order to evaluate the suitability as cover material for plugs, and as minor component (5% v/v) in substrates for vegetable seedlings. Data from cultivation trials showed encouraging results when AS were used as covering material. In comparison with vermiculite, AS influenced foliage growth in many cases reducing plant height, improving seedling compactness, dry matter and final quality. Moreover, an improvement in seedling quality was observed when AS were added to peat based substrates. Likewise, when used as a cover material, seedlings look more compact, and showed a higher dry matter and chlorophyll content compared to the control

Organic growing media : constituents and properties

Organic growing media are essentially bulk products. Availability in large quantity allied to its excellent air and water retention, low pH and salinity, and freedom from pests and diseases has led to peat being the dominant organic constituent of growing media in many parts of the world for the last 50 yr. The unique microporous properties of Sphagnum peat and its resistance to degradation are matched by few other growing media constituents. Nevertheless, local scarcity of Sphagnum peat and the expense of transport has led to the use of other materials in growing media. Notable among these is coir, which unlike peat, a CO2 sink, is widely regarded as a rapidly renewable resource. Indeed, advances in processing and quality control in situ have led to a huge upsurge in the export and use of coir in growing media, particularly in Europe but also in the western United States. Locally available organic materials such as bark, composted materials including green (yard) wastes, municipal solid wastes, and even sewage sludge are also used in growing media. While possessing advantages such as the high air content of bark and nutrient supply of many composted materials, these media components may have disadvantages, from limited supplies due to bioenergy pulls and N lock-up in bark, to physical, chemical, and microbial contaminants in composts. Current innovative approaches involve increasing use of wood fiber in Europe, whole pine-tree thinnings in the United States, and realizing the use and transformation of composted wastes as next-generation constituents of growing media

Liming power of different particle fractions of biochar

The alkalinity given to many biochars by the ash content can be exploited for neutralizing the acidity of peat. Moreover biochar can give to growing media additional benefits, promoting water and nutrient retention and availability, and darkening pale substrates. We studied the effectiveness of an alkaline biochar from pine wood (pH 10.2) in correcting the acidity of a white peat (pH 4.2) both on the 0-10 mm biochar (B0) and on three particle-sized fractions (B1=10-6 mm; B2=6-3.3 mm; B3=<3.3 mm). Seven volumetric percentages of B0 (0, 2.5, 5, 10, 20, 30 and 40%) were tested. The doses 30% and 40% of B0 were the most effective in adjusting peat pH to moderate acidic values and they were used in assessing the role of particle size on liming ability of biochar. The 22 days incubation trial showed that stabilization occurred after 14 days incubation and that the finest fraction had the highest neutralizing power. A comparison between the liming effect of biochar and of calcium carbonate was also performed. We showed that additional benefits of biochar include physical properties such as an increase in air content, a reduction in water availability and a lower shrinkage. These preliminary results suggest that biochar can be used in place of lime in peat based growing media

Mineralization/immobilization of nitrogen and phosphorous in composted growing media

The effects of different temperature and moisture regimes of a composted growing medium on N and P plant-availability and main differences with a peat-based growing medium have been evaluated during laboratory incubation experiments. The influence of root growth has also been tested by plant growth experiments. Microbial biomass and extractable N and P have been determined during a time-course incubation up to 56 days. The microbial biomass carbon (Bc) was relatively high in the composted growing media (2900\u20133600 \u3bcg Bc g-1) but less influenced by treatments. In contrast, Bc was much lower in peat-based growing media (350\u2013600 \u3bcg Bc g-1) but more modified by the incubation conditions, especially by drying/rewetting cycles and by root growth. On the other hand, mineral N and extractable P were much less affected in the peat-based growing media than in the composted growing media. The cyclic changes of moisture regimes in particular, produced a much higher mineralization rate. In the composted growing media, small changes in soil microbial biomass were associated with larger changes in microbial activity