Balanced fertilization: Food for thought
And he gave it for his opinion, that whosoever could make two ears of corn or two blades of grass to grow upon a spot of ground where only one grew before, would deserve better of mankind, and do more essential service to his country, than the whole race of politicians put together."
-- Gulliver's Travels, JONATHAN SWIFT
"Upon this handful of soil our survival depends. Husband it and it will grow our food, our fuel and our shelter and surround us with beauty.
Abuse it and the soil will collapse and die taking man with it."
--VEDAS
Plants form complex organic matter from carbon dioxide in the air, energy from sunlight, and water and nutrients taken from the soil. Balanced nutrition is one of key components of sustainable agriculture. Fourteen elements are indispensable for plant nutrition and divided into 3 subgroups: macro or primary nutrients, nitrogen (N), phosphorus (P), potassium (K); major or secondary nutrients, calcium (Ca), magnesium (Mg), sulphur (S); micronutrients or trace elements, eight other elements.
Focusing on the three major elements, a crude analogy can be drawn with human nutrition. Just as how we need to consume carbohydrates, proteins and fats in certain ratios ie too much carbohydrate or protein or fat results in imbalance, likewise the plant must uptake N, P, K in balance. These 3 primary elements are the usual crop yield-limiting factors, although given our geology there are also widespread sulphur and zinc deficiencies. Crops need all the nutrients in sufficient amounts, although an excess of some of the elements may be toxic to plant. Crop yield will be limited by whichever nutrient is least available eg if K is only 50% present, then yield will be limited to 50% regardless of all other nutrients being 100% available. This is a simplistic expression of the 'law of the minimum'
Nutrients come from soil reserves, animal manure, green manure and plant residues, biological nitrogen fixation through soil bacteria, irrigation water and aerial deposition, and mineral fertilizers.
Soil health is not just about the import and export of nutrients, the organic matter levels have to be maintained with soil structure and humus content. This allows a healthy environment for soil organisms, optimises nutrient and water-holding capacities, and provides important buffering against sudden changes in soil acidity. The science of soil is incredibly complex with the interactions between nutrients, water, air, and organic content, still not fully understood.
What we do know is the first step to ensuring crop yields is to follow the 'law of the minimum' with respect to the primary elements and then figure the next limiting factors through trial, research and observation. Without balanced fertilization, farming becomes inefficient and valuable resources such as labour, water, nutrients, power/fuel are literally thrown away and long term soil health undermined. Proper plant nutrition also ensures a quality produce which may give better farmer incomes and also better diets to consumers. Healthier plants are less susceptible to diseases which may lower the need for plant protection products.
Since 1971, the population of Bangladesh has doubled and food production has matched this both quantitatively and qualitatively too, with a greater variety of food items. There also has been tremendous growth in production of animal protein through the poultry and fishery sectors. All feed for animals and food for humans originate from plants.
Food production is a function of crop yield, number of crops per year, and cultivated area. A sustainable food production implies that available resources are used as efficiently and equitably as possible, resources in this respect meaning:
Natural resource - the availability of suitable agricultural land, fresh water, nutrients and energy
Technology - genetic improvements of crops and animals, plant protection, irrigation, machinery and equipment, access to cheap and reliable transport
Knowledge - its generation, maintenance, transfer and adaptation into agricultural management practices
To keep food production at levels matching population growth, assuming no increase of productive land by leasing or colonization, the future challenges will be to increase yield per unit, maintain soil productivity, better resource management eg water-use efficiency, breeding new crop varieties, increasing research and farmer advisory services, all in the backdrop of climate change. The keystone is balanced soil and plant nutrition.
The writer is Director, NAAFCO ( PVT) LTD
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