How successful fruit growers monitor their crops

All the nutrients in the system must be balanced

The fruit grower must consider a system in balance, if he or she is to understand where all the nutrients are going. We will look at the full system of testing and explain at each point why it is necessary to check and what kind of problems can be experienced at each stage.

Water pre fertigation

Water is often very varied from location to location. There are three main sources of water, and a fourth which is rarely used on mass. In order of most used: bore holes, rivers & streams, mains water and rain water. Rain water does supply water to rivers and indirectly mains and bore holes, however if collected it can be considered a fourth source.

• Bore hole water filters through the soil and rocks that make up part of the soil substructure of the area. As it filters through, it collects the nutrients from its surroundings. Much of the UK's underlying geology is calciferous. As a result bore hole water is often rich in calcium or bicarbonates. We also see heavy metals in some areas, a result of an industrial past, filtered in to the rocks.
• River water behaves much the same way as bore hole water but the uptake is as little as the past couple of years, as opposed to 100’s of years of filtration. The geography of your river source is important. Also knowing what businesses lie up and down stream of your farm can be important to understanding the nutrient content of river water. Down stream is important to remember as your outlet water will filter back in to your river.
• Mains water, drinking grade water considered pure, but as an irrigation source mains will contain some nutrients used by the water company to balance the water, (e.g. fluoride, previously a popular nutrient in use). Mains water is expensive to use as an irrigation source but sometime the grower has no other source.
• Rain water, by far the best source as by contrast most rain water is completely free of nutrients at a balanced pH level, although initial outlay in the collection infrastructure makes its use less desirable. As an input irrigation water, rain water is the best.

Regardless of the type of initial irrigation water, a first water sample must be taken for a nutrient and pH. Your agronomist or nutrient adviser can then work out what should be applied to the water to both buffer it and feed the crops, depending on crop stage. It is essential to know the pH as most UK water is alkaline and most soft fruit programmes are acidic, by contrast most top fruit and vines are neutral to alkaline.

An agronomist or nutrient adviser can help work out your nutrition programme

Water post fertigation

Once past the fertigation shed a second water sample should be taken, this sample will tell the grower if the fertigation equipment is working correctly. The equipment is normally computer controlled though it should be checked at least once per season to be sure it is calibrated correctly. Other issues which may arise include how well blended the fertigation mixture is. Mixing Calcium with Iron can be problematic as they can react to make gloopy blobs, which block the irrigation system. Using a high quality fertiliser mitigates this issue, but awareness of the potential issue means it can be monitored and managed.

Water into bag

A water into bag sample is recommended to be taken more often, such as bi-weekly or monthly. At this point the irrigation water has passed through a full system of plastic pipes and valves. The pipes can, on occasion, cause issues from debris during use, contamination of cleaning products. or if new, contamination of manufacturer products. An example of this is the use of chlorine to clean through pipes after manufacture. Should chlorine enter the fertigation system it bleaches the leaf of the crop while at the same time interfere with the E.C. readings. All growers are recommended to flush the irrigation lines at regular intervals to mitigate this issue, unless the lines are just used for the one set of crops.

Measurements in the bag

• Electro conductivity (E.C.) meters are a hand held device used to measure the Electro Conductivity of the root zone of the crop. E.C. meters measure the number of ions present between the points when inserted into the substrate of the bag. When using E.C. it is important to continue to sample the system. The E.C. in agriculture is ONLY a guide of what is going on. E.C. does not tell you which ions are in the bag, thus which nutrients are in high supply. It cannot distinguish between Chlorine and Nitrogen, nor can it tell you about uptake, lock up or losses. It should be considered a snapshot of the bag at that point. It is important to measure EC at the same time of day each time for consistency as E.C. can fluctuate within the day, depending on crop uptake. Most soft fruit growers or breeders recommend a target E.C., all things being correct, for a grower to stick to.
• Leaf analysis involves collecting 100 leaves and posting them to the lab for analysis, tells the growers what the plants have actually taken up from the fertigation mixture. This is the best way to assess what the plants are doing at each stage of their development.
• Substrate or soil analysis is the best measure of what exactly is sitting in the bag. You would expect to find calcium, phosphorus, iron and other immovable or less available nutrients locked in the bag, though if its present you may also find chlorine locked in the bag. This measurement tells the grower if he can or cannot rely on his E.C. meter. If he can rely on the E.C. knowing what’s in the bag means he can save much money on lab analysis.

Water out of bag

The fertigation water should be set up to run out of the bag to the tune of 12% of the volume going into the bag. Water out will most likely contain NPK, though more N than anything else as its highly mobile in water. It may contain Chlorine which is a sign to soil sample the bags and attempt to trace where the contaminate is getting in to the system. Water out, if measured over time with water in, will allow the grower to see how the crop is responding to the fertigation mixture and what improvements or savings can be made against the mixture for future years.

The balanced sum of all nutrients should be zero

If the grower has all the information, a calculation can be made to show that the balanced sum of the data is zero. That means all the nutrients in the system have been accounted for. As the mixture is changed from vegetative mixture to flowering mixture, the change in E.C. and water/out measurements should define the change, in addition to looking at the crop and tasting the fruit.

Yara analytical services for fruit growers 

Yara Analyical Services are able to conduct a complete range of analyses. For more information on any of these analyses or services please click the link below