Greenhouse Plant Nutrition
Greenhouse Plant Nutrition
The subject of plant nutrition is very complex and it is not possible here to give more than an elementary background to it. In a great deal of what is written about plant nutrition, assumption rather than fact plays a very large part. As with the physiological aspects of plant growth, it is convenient to consider nutrition in a sectional manner.
Here again, there is such a complex relationship between all the nutritional elements and chemical processes that the ability of one chemical element to fulfil a role depends a great deal on the activity and presence of all the others. It could be said that each chemical element is a cog in a large wheel, and should a cog be missing some malfunction or complete breakdown of vital processes is likely. It is, however, true to say that the greenhouse gardener has matters under his control to a much greater extent than the gardener out of doors. He also has the ability to meter the quantity of each particular chemical element supplied to the plant.
All living organisms require a range of essential chemical elements if they are to generate the energy to carry out all the various processes concerned with their growth and development. Animals can take in food and drink in either solid or liquid form and digest the chemical elements in them, but living plants take their ‘food’ only in soluble or gaseous form, this being true even of insectivorous plants which ‘digest’ their prey. The majority of elements are assimilated by the roots, and carbon and oxygen are absorbed through the leaves. A plant nutrient is therefore a chemical which has a precise function in the plant’s growth and a vital part to play in the plant’s further development.
The range of essential nutrients
The nutrient content of a mineralwill vary according to the constituents of the native rock from which the soils were originally derived, the treatment which the soil has received over the years and the weather pattern. One could scarcely expect a cultivated light sandy soil in a very wet district to be rich in nutrients; these would tend to be washed or leached out. On the other hand, a light sandy soil which had supported a good cover of growth in a dry area could be surprisingly rich in plant nutrients. Clay soils tend to be richer in plant nutrients than light sandy soils, being invariably richer initially in plant nutrients which are not leached out so rapidly.
The range of mineral elements or plant nutrients varies from soil to soil in different regions, but they invariably contain the macro-elements phosphorus, potassium, calcium and magnesium, along with the micro-elements silicon, aluminium, sulphur, boron, manganese, copper, zinc, iron, molybdenum, chlorine, sodium, iodine, cobalt, selenium, and others less well known. In addition, the major element nitrogen is supplied by the breakdown of organic matter and by fixation (synthesis from the atmosphere), and hydrogen and oxygen are supplied 90-95% by water and carbon in gaseous form from the atmosphere.
While the natural complement of these elements may well suffice to sustain a plant growing naturally out of doors, this is not the case in realms of intensive greenhouse culture, which means resorting to the application or addition of these nutrients, particularly those of the macro category which are used in large quantities by most actively growing plants.