B. Gunnlaugsson, G.K. Gudfinnsson and S. Adalsteinsson
Agricultural University of Iceland, Reykir Ölfusi, 810 Hveragerdi
Abstract
Greenhouse vegetables (i.e. tomato, cucumber, sweet pepper) exhibit a large and continuous nutritional demand. In organic cultivation, it is not possible to supply all the nutrients needed in one application at the beginning of each planting. Mushroom compost, fish-meal or fish- silage are all potential organic fertilisers to supply plants with nutritents throughout the season. Applying these fertilisers at adequate rates will ensure comparative yields to conventional cultivation of greenhouse vegetables.
Keywords: organic fertilisers, greenhouses vegetables, fish products, mushroom compost
Introduction
Organic production relies solely on organic fertilisers to supply the necessary nutrients to plants. Greenhouse vegetables i.e. tomato, cucumber and sweet pepper have a high nutritional demand and fertiliser must be applied regularly throughout the growing season in order to fulfil their needs. Because organic fertilisers are less concentrated than inorganic ones a larger volume of them has to be applied to supply the same amount of nutrients to plants. This will make the cost of fertilisation higher because the cost per amount of pure nutrients is higher and more amount of labour is needed to apply them. In order to keep down costs of fertilisation, it is of importance to choose fertilisers carefully which give the right amount and balance of nutrients and to develop methods to spread them fast and accurate.
Mushroom compost is a nutritious waste product from conventional mushroom production available in abundant amounts at a low price. It has been used with good results as a soil amender and fertiliser in Iceland for a number of years and is accepted as a source of nutrients in certified organic production with certain restrictions. Preliminary trials have shown that it can serve well as a fertiliser in cultivation of tomato (Gunnlaugsson 1997, 1998). Apart from being very nutritious, mushroom compost also has beneficial effects on soil structure as it contains abundant amount of un-decomposed organic material.
Fish products such as fish-meal and fish-silage are rich in nutrients and can thus serve as fertiliser to plants. As the nutrients are more concentrated in these materials than in mushroom compost it is possible to fulfil the needs of plants for nutrients by applying fairly low volumes and they are available at a reasonable price, at least in Iceland. In this article experiments with the three above mentioned organic fertilisers for greenhouse cultivation of cucumber are described.
Materials and methods
Cucumbers where grown in a 216 m2 greenhouse on raised beds (8.00 x 1.00 x 0.30 m) which where filled with a commercial soil mix of Icelandic peat (48%), fresh mushroom compost (40%) and Hekla-pumice (12%), mushroom compost thus functioning as a base fertilizer for the plants. Two plantings where performed with cv. ‘Mustang’ and cv. ‘Ventura’ respectively. The plants where trained to high wire system with plant density of 2.4
plants/m2. The first crop, cv. ‘Mustang’ was sown on March 20th and planted on April 17th. Harvesting period lasted for 8 weeks (May 17th – June 30th). The second crop, cv. ‘Ventura’ was sown on June 3rd and planted July 1st. The harvesting period lasted for 12 weeks, from July 25th-October 20th. Temperature was set at 22°C during the day and 19°C at night with ventilation at 24°C. At daytime, carbon-dioxide was supplied at a concentration of 700 ppm when the vents where closed and 340 ppm when they where open. Irrigation with water took place 4 times a day, in 3-5 min cycles through a drip-tape.
There are large differences in the nutrient content of each fertiliser used in the experiment (Table 1). Mushroom compost is very high in potassium but low in nitrogen and very low in phosphorus compared to the other fertilisers. Fish-meal has a very high content of nitrogen and phosphorus but a moderate content of potassium. Nutritional values for fish-silage are considerably lower than for fish-meal, especially phosphorus.
Table 1 – Content of nitrogen, phosphorus and potassium in the organic fertilisers used in the experiment.
Total N g/kg Available N g/kg P g/kg K g/kg Mushroom compost (bulk density 462 g/l) 11.0 5.5 0.9 12.6
Fish-meal 96.0 76.8 39.4 5.6
Fish-silage 18.6 15.0 3.3 3.8
Table 2. Fertiliser application for cucumber and estimated total amount of nitrogen, phosphorus and potassium given in the experiment by each fertiliser. The amounts given are per m2 greenhouse area.
Mushroom compost
Fish-meal Fish-silage Base fertiliser, g/m2
(soil mix with mushroom compost)
17,311 17,311 17,311
Additional fertiliser, g/m2 17,736 1,039 2,439
Estimated total application of N, g/m2 193 175 132 Estimated total application of P, g/m2 32 57 24 Estimated total application of K, g/m2 379 194 197 The weekly nutritional demand for cucumber was estimated to be 5.02 g N, 1.0 g P and 6.28 g
K per m2 greenhouse area giving a total demand of 136 g N, 27 g P and 170 g K per m2 greenhouse area for the cultivation period in the experiments (27 weeks). Base fertilisation with mushroom compost was the same in all the beds, 17,311 g equal to 95 g N per m2
greenhouse area (Table 2). Additional fertilisation with mushroom compost, fish-meal or fish-silage was started one month after planting. Because of the large differences in nutritional content of the fertilisers, it was decided that the doses given to the plants should fulfil their estimated need for nitrogen. Thus, 900 g mushroom compost, 65 g fish-meal and 335 g fish-silage per m2 greenhouse area where applied on a weekly basis throughout the season. The total amount of each fertiliser applied is given in Table 2 as well as total estimated amount of nitrogen, phosphorus and potassium.
Results and discussion
Total saleable yield for both plantings (21 harvesting weeks) ranged from 30.3 - 36.9 kg/m2 highest when applying mushroom compost, lowest when applying fish-silage (Table 3). Normal saleable yield for cucumber in Iceland is 40-45 kg/m2/year in conventional cultivation for harvesting periods of 29 weeks giving a average of 1.5 kg/m2/week. In this experiment the average saleable yield varied from 1.44 - 1.75 kg/m2 which is highly comparable to conventional cultivation.
Table 3. Saleable yield of cucumber plants cv. ‘Mustang’ (1. planting), cv. ‘Ventura’ (2. planting) and total yield when fertilised with mushroom compost, fish-meal and fish-silage. Values are means + SD.
Fertiliser
1. planting ‘Mustang’
2. planting ‘Ventura’
Total saleable yield
kg/m2 kg/m2 kg/m2
Mushroom compost 17.1+1.2 19.9+1.3 36.9+1.0
Fish-meal 20.1+1.2 15.5+2.5 35.6+3.1
Fish-silage 15.0+1.9 15.3+1.0 30.3+2.1
In the first planting the highest yield was obtained when applying fish-meal as additional fertiliser whereas the plants fertilised with fish-silage gave the lowest yield. The lower yields might be explained by the fact, that undiluted fish-silage was accidentally applied early in the season, causing temporary root death. In the second planting on the other hand, the fish- products gave considerably less yield than the mushroom compost which could partly be explained by the fact that mushroom compost has favourable physical properties. When the soil was examined at the end of the season it was clearly lighter and better aerated in beds fertilised with mushroom compost.
When comparing the nutritional demand of the plants and the amount of fertiliser given it is clear that in some cases to much fertiliser was applied (Table 2). It is therefore interesting to look at the actual nutrient status in the soil during the experiment. Nitrate is below target value except in the very beginning and the two latest measurements when fish-meal was applied as a top dressing (Figure 1). No signs of nitrate shortage where observed on the plants, therefore it is evident that the nitrogen released from the organic material was either taken up simultaneously by the plants or washed out. The potassium level was very high in the beginning of the season because of the high potassium levels in the mushroom compost but decreased steadily towards the end of the season when fish-meal and fish-silage where applied as additional fertilisers (Figure 1). On the other hand, very high values where measured when plants where fertilised with mushroom compost, again because of high concentration of potassium in the mushroom compost.
Potassium 0 200 400 600 800 1000 1200 1400 1600 28 -A p r 12 -M a y 26 -M a y 9- Jun 23 -J un 7- Jul 21 -J ul 4- A u g 18 -A ug 1- S e p Fish-silage Fish-meal
Mushroom compost Target value
Nitrate 0 50 100 150 200 250 300 28 -A p r 12 -M a y 26 -M a y 9- Ju n 23 -J un 7- Ju l 21 -J ul 4- A u g 18 -A u g 1- S e p mg/ l Fish-silage Fish-meal
Mushroom compost Target value
Figure 1. Level of nitrate and potassium in soil samples from cucumber beds fertilised with fish-silage, fish-meal and mushroom compost. Target values from Bjerggård and Hansen (1985).
Conclusions
The three different fertilizers used in the experiment have different nutritional values and physical properties. Mushroom compost contains high amount of relatively un-decomposed organic material giving the soil good physical properties. On the other hand a large amount of the material (20 kg/m2/season) is needed to fulfil the demands of the plants for nitrogen resulting in excessive fertilisation with potassium. Fish meal is very rich in nitrogen and phosphorus and fish silage contains a relative high amount of nitrogen, but these materials do not contribute to preserve favourable physical properties of the soil. To give the plants optimum fertilisation and soil conditions it is probably best to apply these organic fertilisers as a mixture. In a subsequent experiment a mixture of mushroom compost and fish-silage proved to be a good alternative (Gunnlaugsson, manuscript).
References
Bjerregård, A. and M. Hansen 1985. Jord, vand og næring. GartnerInfo, Köbenhavn. 125 p. Gunnlaugsson, B. 1997 Sveppamassi sem áburðargjafi í lífrænni ylræktun – Ræktun tómata
1996. Garðyrkjufréttir nr. 201. 7 p.
Gunnlaugsson, B. 1998. Sveppamassi og fiskmjöl sem áburðargjafar í lífrænni ylræktun. Garðyrkjufréttir nr. 203. 7 p.