Climate change causes phosphorus loss

Crop growth, including Canna, can be adversely affected if predicted changes in rainfall patters over the coming years prove to be true, according to research published in the journal Biology and Fertility of Soils.

Scientists from North Wyke Research, in the UK, say they have determined for the first time how the rate at which dried soil is rewetted affects the amount of phosphorus lost from the soil into surface water and subsequently into the surrounding environment.

For those short of biology facts, phosphorus (P) is an essential part of the process of photosynthesis. It helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress. Phosphorus effects rapid growth, encourages blooming and root growth. It often comes from fertilizer, bone meal, and superphosphate.

Dr Martin Blackwell, one of the project leaders, said the study's preliminary results show the changing climate might limit the ability to mitigate phosphorus losses at certain times of the year, especially summer.

"This is really worrying because high phosphorus concentrations in surface waters can lead to harmful algal blooms, which can be toxic, cause lack of oxygen during their decay and disrupt food webs," said Blackwell. "This can also affect the quality of water for drinking and result in the closure of recreational water sport facilities."

Mineral deficiences in plants

In botany, chlorosis is a condition in which leaves produce insufficient chlorophyll. As chlorophyll is responsible for the green colour of leaves, chlorotic leaves are pale, yellow, or yellow-white.

The affected plant has little or no ability to manufacture carbohydrates through photosynthesis and in extreme cases may die unless the cause of its chlorophyll insufficiency is treated. Specific nutrient deficiencies (often aggravated by high soil pH) produce chlorosis, which may be corrected by supplemental feedings of missing compounds in various combinations. Different mineral deficiencies act in subtly different ways.

Deficiency of Nitrogen (N)
The characteristic deficiency symptom of nitrogen is the appearance of uniform yellowing of leaves including the veins, this being more pronounced on older leaves. The leaves become stiff and erect. If the condition of nitrogen stress persists, then the result is decreased foliage and shoot growth.

Conditions inducing Nitrogen deficiency include heavy rain causing leeching, low organic matter content of soils, denitrifcation (losses of N2 and N2O to the atmosphere).

Deficiency of Magnesium (Mg)
Magnesium deficiency causes yellowing, but differs from that of nitrogen. The yellowing takes place in between veins of older leaves and veins remain green, this is followed by necrosis (unnatural death) of tissues. Interestingly, Mg deficiency may be induced in tomatoes by high levels of ammonium in the nutrient solution (Kafkafi et al., 1971).

Deficiency of Iron (Fe)
The principal veins remain conspicuously green and the surrounding portion of the younger leaves turn yellow. Conditions inducing Iron deficiency include calcarous soils, soils high in P, Mn, Cu, or Zn, high rate of liming.

Deficiency of Potassium (K)
Under potassium stress condition, the yellowing of leaves starts from the tips or margins of leaves extending towards the center of leaf base. The yellowing is interveinal and these yellow parts become necrotic (dead spots) with leaf curling.

These are some of the more common causes of mineral deficiency, and as there are many more minerals making a contribution to the Cannas growth, then we can see that these are the first causes that should be investigated when chlorosis is spotted on foliage.

What is the best way to overcome these Environmental deficiences? Well, that is obviously to deliver the missing minerals to the chlorotic plant. The best immediate source of trace minerals is a liquid feed with seaweed fertilizer. However, that is only a temporary fix, as the basic soil deficiency has to be corrected by introducing the missing element(s).

And what happens if there is no improvement from the upgraded feeding regime? Then it is now time to think the worst and start considering the possibility of chlorosis induced by Canna virus, more of which later.

Fertilizers and crop rotation

Most people think of Cannas as being just a flower... wrong! Canna is an agricultural plant that has been recruited into floriculture. No vegetable gardener worth his salt would ever dream of growing a crop of root vegetables, which is what Canna is, in the same ground for a second year, a good farmer or gardener rotates his crops.

Monoculture, the continual growing of a single crop on the same ground, supported completely by chemicals has become questioned in recent years. It is true that vineyards, and orchards are examples of successful monoculture, but plants as greedy as Canna do not fall into the same category.

Crop rotation or crop sequencing is the practice of growing a series of dissimilar types of crops in the same space in sequential seasons for various benefits such as to avoid the build up of pathogens and pests that often occurs when one species is continuously cropped. Crop rotation also seeks to balance the fertility demands of various crops to avoid excessive depletion of soil nutrients. Crop rotation can also improve soil structure and fertility by alternating deep-rooted and shallow-rooted plants.

A low nitrogen level will leave Canna foliage with yellow striata, and slow its growth rate. Phosphurus helps with the transformation of solar energy into chemical energy; proper plant maturation; withstanding stress. Potassium helps in the building of protein, photosynthesis that keeps the foliage a consistent green, and reduction of diseases. As can be deduced from that, deficiencies in theses basic macronutrients can result in unhealthy plants with effects that can be mistaken for Canna virus. Those are only the three primary nutrients required for healthy plant growth, and many others are required in sufficient quantities to provide healthy, vigorous growing conditions.

Crop rotation is also used to control pests and diseases that can become established in the soil over time. Plants within the same taxonomic family tend to have similar pests and pathogens. By regularly changing the planting location, the pest cycles can be broken or limited.

Cannas grow remarkably quickly, and to do that they require great supplies of both nutrients and minerals. A good canna crop means that the soil is now stripped of most food and minerals. It needs a way of being replenished. Of course, in a small garden, you can swap Cannas from one bed to another, or even swap the soil between the beds, enriching it at the same time. Farmyard manures is the traditional preferred choice, but for those who do not access to that, then there are many safe packaged alternatives.

When making a fertilizer selection, remember that it is not only nutrients, mainly the big three of nitrogen, phosphorus, and potassium, but also the neglected calcium, magnesium and sulfur, and also the trace elements that are necessary in minute quantities for the proper growth, development, and physiology of the Canna, i.e. iron, manganese, boron, copper, molybdenum, nickel, chlorine, and zinc.

In fact, there are 72+ biological trace elements in all, and many people are concerned about the historic agricultural focus on the big three elements, as over time, their residues turn into salt and eventually make the soil sterile and un-arable. Millions of acres in North America and elsewhere have already become too salty to grow anything. It is a huge problem, compounded by damaging 'fertilizer runoff' into our rivers and water tables. Such a 'complete spectrum', 72+ trace element fertilizer can be easily obtained from seawater, since the seas contain all of the 92 elements of the Earth in suspension. Fertilizers based on seaweed are particularly efficient at restoring many of the missing, ignored trace elements.

A green manure, ready for ploughing into the soil, about 3 weeks before planting with Cannas

Also, in the northern climates, one method of assisting is to take advantage of the 5-6 winter months when Cannas are safely indoors and the land lays fallow, just growing some tough old weeds. The technique is to grow a green manure crop over winter, which can be ploughed back into the ground come the following spring. This enriches the soil, interrupts the pest cycle, with the added benefit of suppressing weeds over the winter months. Combine that with mulching over the Canna growing season and you can be on your way to providing perfect conditions for growing perfect Cannas.

After thought:
Linus Pauling, winner of 2 Nobel prizes, stated: "You can trace every sickness, disease or ailment in the human body to a mineral (trace element) deficiency." Surely, that applies to our Cannas as well?