Plant nutrition is the study of the chemical elements and compounds necessary for plant growth, plant metabolism and their external supply. Without proper plant nutrition, plants tend to die off or produce little or no yield.
In my line of work I visit hundreds of flower farms a year; the flourishing, the ticking over, and the ones in dire straits. A lot of my more demanding work is dealing with farms that suddenly run into problems. “Ruth, please come and visit our farm as soon as possible, our production has suddenly dropped to half” is a common call. My advice to flower farmers on the critical issues in plant nutrition in floriculture would be as follows:-
Start with the basics, understand your soil and water and know what you are dealing with. A solid ‘risk’ assessment before you even buy the farm is recommended.
Do a complete soil analysis, soil texture analysis, nematode count, pathology screen and irrigation water analysis. Now you know what you are dealing with and can work out the economics. It’s better to get a shock now than after your investment has already been sunk in land & greenhouse infrastructure.
Before planting in the soil, balance the cations, pH, organic matter and phosphorous levels by adding scientifically calculated soil corrections from the complete soil analysis. Deep rip the soil to break up compaction zones and mix the soil correction in well. Do not turn the luscious topsoil over and bury your existing organic matter and microbes.
Good land preparation and soil correction will hold you in good stead further on down the line, when your beginner’s luck is over. Put in place an annual SOIL HEALTH PROGRAM – to analyze and adjust cations, pH and organic matter for maximum soil & plant health and fertiliser efficiency.
Buy a fertigation system that is suitable for your water quality and can handle your gradients and can deliver the maximum water requirement on the hottest day. Plan a proper fertigation program based on the plant size, plant type, production, water quality and soil type. Take quarterly soil samples for a 1:2 SGF analysis so that you know what’s happening in the soil and can deal with it before it becomes a problem.
Back this up with leaf analysis to make sure there is no ‘hidden hunger’ in the crop limiting your production. Identify problems early before they hit your bank balance.
Before planting in media, do a media analysis, nematode count and pathogen screen. The certificate of testing that comes with your coco-peat does not account for the conditions the coco-peat has traveled or been stored in. The fine pumice or gravel from the nearby quarry could have sodium, toxic metals, silt and nematodes.
Do bi-annual nematode counts. You can’t see nematodes with the naked eye, and by the time your plants go yellow, you will have lost much of your production and quality. It is also easier, cheaper and more environmentally friendly to treat low nematode levels with biological products. Once levels get out of control you may have to resort to more toxic and persistent chemicals. Nematodes severely affect plant nutrition and disease pressure.
Water testing is crucial. Borehole water tends to have a more constant quality and tests are advised twice a year. Surface water quality can vary dramatically depending on rainfall and evaporation. Rain water is best – plan to catch as much of this as possible. Water quality has a major impact on your plant production and health and the way you manage your irrigation. Common problems in Kenya are high sodium and high bicarbonates.
If your water has high sodium reverse osmosis can reduce the sodium, this is expensive to install and maintain. Water can also be missed with rainwater to bring the sodium down. If you use high sodium water you should monitor the sodium levels in the soil. Plants can grow along happily with a small amount of sodium in the soil but when it reaches a critical level you will get a rapid decline in production and plants will become very susceptible to diseases. As the sodium levels build up the soil structure deteriorates which becomes very difficult to fix.
Work with humic acids and calcium products in conjunction with leaching to flush the sodium out. This is where a good soil survey and land preparation hold you in good stead. Water saturated soil, bedrock, compaction layers and unbalanced cations will all impede successful leaching of saline soils.
Water can have high bicarbonates these bind with calcium and magnesium to create a free lime deposit in the soil that raises the soil pH and locks up phosphorous and micronutrients Once the free lime has built up in the soil, it can be very hard to deal with. Much better to treat the problem at source and acidify the water.
Acidification can result in an increase in nitrates from nitric acid or phosphates from phosphoric acid and the fertigation program should be adjusted to balance these. Quarterly drip analysis will check the Electrical Conductivity (EC), pH, nutrient, and bicarbonate levels of your drip water and ensure that everything is going to plan. On-farm daily EC and pH measurement are advised.
Many farms have tripped up due to water quality and fertigation system faults that were not picked up soon enough.
A very common cause of yield and quality collapse is water. Some farms very admirably collect rainwater, which has low salts and is fairly neutral. When the rainwater runs out the farm then changes to borehole water which may have a high EC, high sodium and high bicarbonates. As soon as the water source changes the fertigation recipe should change. By the time your plant shave gone yellow – you are already on a down hill production curve.
Get a soil water meter, or go around the farm often with an auger to check soil moisture levels. Water you see on the surface is not what the roots see underground. Over and under watering affect nutrient uptake and production.
Over-watering kills your plant roots, microbes and soils and causes leaching and loss of fertilisers. It can cost you unnecessary money and pollute the environment. Anaerobic cold wet soils really increase disease pressure on your plants. Sitting water on the soil surface (even for a few minutes) can spread diseases very fast through your crops.
Underwatering, which is very uncommon, causes plants to wilt, which causes tissue damage and secondary infections (botrytis and downy mildew).
Be especially vigilant on soil moisture when the weather changes. We are on the equator and can have a very hot day in the middle of the cold season, where the water demand of the crops shoots up for a few hours and plants wilt. Like wise we can have a few rainy days in the middle of the hottest season, the plants water requirement shoots down and the soils get waterlogged.
Analyze, analyze, analyze. It will save you money in the long run. Plan the analysis that you need and budget accordingly. Read, understand and benefit from your analysis results. Don’t file them in the drawer until the next audit. Audits are meant to guide you and there is a reason they recommend you do these analysis! If you don’t understand anything, just ask! Or get a professional consultant in.
The iron chelate salesman s will most probably find an iron problem in your crop. The person selling nematicides will always find a few nematodes that need treating. That’s their job.
The suppliers have done extensive tests on their products before they write the labels and take their products to the market. A little bit of product used properly can have a brilliant result. Don’t be tempted to over-use or over apply products. I have seen some catastrophic results from product over use. Ditto underuse!
If all goes well – analyze so that you know what you are doing right and can do it again (and again and again….) If all goes wrong – don’t over complicate things, go back to the basics, call in the professionals, analyze, and recover faster!
Having covered the basics, let’s switch gears a bit and explore the role of plant nutrients in controlling insect pests and diseases in plants.
Till next time,
Ruth Vaughan is the Technical Director at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). Ruth is also a contributing author to Kenya’s leading horticulture magazines such as the HortFresh Journal, HortiNews and Floriculture. Ruth is a great believer in soil health, organic matter, biochar and carbon sequestration as a way to alleviate climate change and increase food security. Loves visiting farmers and seeing all the different farming methods
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