There is increasing interest amongst soft fruit growers in the concept of EC feeding – that is, fertigating their soil grown crops on a continual basis throughout the growing season. Over the past few years, several growers have experimented with the use of constant EC feeding and, without exception, they have found that fruit quality problems have been significantly reduced and yield and fruit size have been significantly increased.
Traditionally, most soil grown crops have been fed on an intermittent basis (eg, once or twice a week) and given a set dose of fertiliser per cropped ha (eg 25kg/ha/week). Whilst this approach allows a controlled amount of fertiliser to be applied throughout the season, the EC levels of the feed and soil fluctuate significantly according to water use and frequency of application. This can result in low soil EC levels, particularly at harvest time due to flushing of fertiliser following large doses of plain water. An increasing number of growers and advisors believe this approach results in significant fruit quality problems and also limits fruit size and crop yield. Fertigating the crop on a continual basis allows the EC and fertiliser recipe to be adjusted according to crop growth stage and soil/leaf/fruit quality assessments at key growth stages.
With many more growers becoming interested in the concept of EC feeding, the following notes provide some guidelines on how best to implement this more technically demanding approach to crop nutrition of soil grown crops.
1. Soil Analysis
Soil sampling should be carried out prior to bed formation so that appropriate pre-plant fertilisers and liming materials can be applied. For plantations going into their second and subsequent years, sampling should also be carried out prior to the onset of growth, ideally in January – February. Analysis should determine available levels of P, K, Mg as well as pH. Determination of Calcium levels also helps in working out the requirements for Gypsum (pre-planting) on soils high in Sodium/Magnesium Carbonate and in working out the level of Calcium Nitrate needed in the fertigation programme. Trace Element analysis of soils is expensive and usually unnecessary (with the exception of Boron) unless there is a history of particular trace element deficiency.
2. Water Analysis
In order to asses the quality of the water source used, its suitability, and the contribution of individual nutrients to crop nutrient requirements, it is necessary to determine the full major and minor element composition of water, as well as pH, EC and Bicarbonate.
3. Calculation of Feed Recipes
Target nutrient levels for particular cropping scenarios have been drawn up, in similar fashion to target levels for peat and coir grown crops. The targets assume soil nutrient levels of: ADAS Index 1 for Nitrogen, Index 3 for P,K, Mg and normal levels of Ca, Sulphur and Trace Elements.
Recipe targets can be adjusted up or down according to soil and water analysis data. For example, on ADAS Index 4 soils, feed levels of P, K and Mg may be reduced by 25% whereas on ADAS Level 2 soils feed levels may be increased by 25%. In addition to soil nutrients, the chemical composition of the irrigation water supply is taken into account (as in recipes for substrate grown plants). The pH of the feed solution is also adjusted to 6.5 by calculation of the acid requirement (from the Bicarbonate level of the water not its starting pH) reflecting the optimum pH level for nutrient availability in soils.
4. Stock Tank Recipes
Stock Tank Recipes can be given using either straight fertiliser sources or proprietary mixes (or a combination of both). Nowadays, many of the commonly used fertilisers are available in liquid as well as powder form such as Hortiflow Liquids or Hortimix solubles. Recipes for vegatative and fruiting growth stages are available from Hortifeeds as are target EC schedules for different growth stages.
5. Application Procedure
Except for particular growth stages (eg immediately post harvest on Junebearing Strawberries), fertigation should be practised at every watering. This will give a more even nutrient distribution and less wastage than intermittent feeding, which can result in much leaching of Nitrate and Potassium and very uneven nutrient distribution within the soil profile. In order to determine that feed is being applied at the correct EC and pH it must be checked by gathering a sample from the irrigation tape at least once a week and verifying with handheld Conductivity and pH meters. A sample of the feed should also be sent to the lab to check that the correct balance of nutrients has been achieved.
6. Crop Monitoring and Feed Adjustment
A crucial part of the success or failure in constant EC feeding revolves around timely and correct monitoring procedures and subsequent feed adjustment. The following is a suggested guide:
(a) Soil EC Measurement
Monitor the EC of the soil by using the Ecoscan 5S Conductivity Probe. Target levels using this device are 100-150 uS for initial growth, increasing to 200-250 uS during flowering and 300-350 uS during fruiting. After harvest, soil EC levels should be reduced to below 250 uS, especially on permanent tunnel sites, in order to avoid a conductivity rise over the winter when plants are being kept on the dry side.
(b) Leaf Tissue Analysis
Leaf Tissue analysis should be carried out at least 3 times during the season, ideally at first open flower, first ripe fruit, and early September. The most important factor with leaf tissue analysis is a rapid turn around of results, so that any deficiencies can be rapidly corrected by adjustment of the fertigation/spray programme.
The guidelines given above have been prepared by Technical Consultant Dennis Wilson. Anyone wanting further information on the subject is welcome to contact us on 01522 704404.
