Some of the factors that affect crop production are explained below: 1. Crop Choice 2. Good Seed 3. Nutrients 4. Crop Enemies 5. Management.
Factor # 1. Crop Choice:
When a country is first settled by Europeans, the first plants grown are usually pioneering crops like the cereals. After a while the pioneers find that these crops do not do well in some areas, and so they choose others which are more suited to local climates. For instance, wheat and oats were almost the only crops grown for many years in the north-west of New South Wales.
Then it was found that this area was suited to other crops such as grain sorghum, linseed, barley and cotton, which are now grown there as well as the wheat. Wheat was once grown extensively on the tablelands of New South Wales until it was proved that spring frosts killed the wheat flowers. Now maize and potatoes have taken the place of wheat in these areas.
When choosing a crop to grow we must first think of markets, for it is not much use growing a certain product if there is no way of selling it. For instance, there are many areas of southern Queensland and northern New South Wales where crops like navy beans would grow quite well, but until proper markets are formed these crops cannot be a success.
Freight charges are other factors which help us to decide which crops to grow. Thus there are many districts well suited to vegetable growing, but the distance from city markets means that freight costs are too high to make it a success.
It is quite certain that climate is the chief factor which governs crop growth. Temperature, rainfall and day length have a big effect on the way any plant grows. Because of this, the climatic needs of some crops have been studied a great deal by scientists, and we can often say exactly what day or night temperature, or what soil temperature a plant needs to make its best growth.
The water needs of crops are also well known. All these climatic needs of crops are called adaptations, and should be learned carefully, for a crop will only grow best when it is planted in the proper climate.
Soils are also important in crop growth. Some crops prefer light sandy soils, others do best in heavy soils. Some prefer deep soils, while others make satisfactory growth on shallow soils. Some crops will never do well unless the soil is rich in nutrients, while others will tolerate poor soils.
In deciding what crop to grow, it is sometimes important to consider the animals carried on the property. Some crops will stand feeding off, but others cannot be used for grazing at all. Some crops which will stand heavy grazing can be used as soil improvers; by feeding off and then ploughing down, the manure of the stock and the plant remains are added to the soil.
Factor # 2. Good Seed:
Farmers anxious to obtain high crop yields must begin by using the highest quality seed. The first essential is that the seed shall be free of disease. For instance, seed potatoes should be certified, guaranteed free of virus diseases. Seed wheat should be treated with copper carbonate dusts to kill the spores of bunt, and all vegetable seed should be certified disease-free. In addition, no sample of seed should contain weed seeds.
The best variety of seed will be the one which has the right length of growing season for the local climate, which is resistant to diseases, and which has a high yield. In cold climates early-maturing or short-season varieties are often chosen because they can be planted late when the danger of frosts is past. Hybrid maize seed, hybrid sorghum, and hybrid cabbage seed are superior to ordinary seed because the plants produce higher yields.
In commercial vegetable growing, farmers must choose their varieties very carefully, for they must know almost to the day when their products can be sold.
Factor # 3. Nutrients:
No crop or pasture will give good yields unless the soils contain the necessary plant nutrients. Plants need to be supplied with nine nutrients in large amounts;
Plants obtain carbon and oxygen from carbon dioxide in the air, and hydrogen from the water brought up from the soil. All the other major nutrients must come from the soil.
Plants also need to be supplied with some nutrients in very small amounts.
These are called the micro-nutrients or trace elements and the chief of these are:
Some of these nutrients may be supplied to the soil in different ways. For example – growing legumes will add nitrogen to a soil. But the quickest way to add nutrients to a soil is to use fertilisers. Fertilisers are substances that are rich in plant nutrients and they are able to add to the nutrients contained in the soil.
There are two main kinds of fertilisers:
1. Organic fertilisers such as animal manures, plant residues, sewage products, by-products from slaughter houses such as blood and bone. These not only supply some plant nutrients but some of them also have very good effects on the physical nature of the soil.
2. Inorganic or chemical fertilisers are very concentrated sources of plant nutrients.
Nitrogen fertilisers include ammonium sulphate, urea and aqueous or liquid ammonia. Ammonia is a by-product of gas-works and coke ovens. When it is treated with sulphuric acid it turns into ammonium sulphate. This fertiliser supplies both nitrogen and sulphur. It is usually applied to the soil after a crop is grown. The nitrogen in it is quickly available to plants, but some of it may be leached out of the soil by heavy rain that comes soon after it is applied.
Urea is a popular nitrogenous fertiliser. It can be made from ammonia. When applied to the soil after sowing, the nitrogen is quickly available but some of it may be lost by leaching if there is heavy rain.
Aqueous and liquid ammonia are applied to the soil before sowing by drilling it into the soil through pipes that go beneath the surface.
Phosphorus fertilisers include bone dust and the various forms of superphosphate. Superphosphate is made by mining rock phosphate from Nauru and Ocean Island and from the Duchess District of Queensland, and treating it with sulphuric acid.
The fertiliser therefore contains some sulphur as well as the phosphorus. It is usually applied when seeds are sown. It is important to place it close to the seeds because some of it is turned into forms which are not available to plants.
Potassium fertilisers include potassium chloride or “muriate of potash”, potassium sulphate or “sulphate of potash” and potassium nitrate. Potassium fertilisers are obtained from potash mines in Germany, Russia, France, Spain, Poland and North America. There are also vast stores of potash salts in the Dead Sea. The potash ore that is mined consists of a mixture of potassium chloride, potassium sulphate and other substances. These can be separated in a factory.
Potassium fertilisers contain this plant nutrient in a readily available form, but it can be leached out by heavy rain. The soils of high rainfall areas are often lacking in potassium. Common signs of a potassium deficiency are white spots on a leaf, or burnt edges to a leaf, or a shortening of the internodes of the plant. Potassium fertilisers are usually applied after sowing, either as the pure fertiliser or in a fertiliser mixture which contains other nutrients.
Sulphur fertilisers include pure sulphur or “flowers of sulphur”, gypsum or any sulphate of a metal element. They are applied before or after sowing and are usually quickly available.
Calcium fertilisers include ground limestone, dolomite and slaked lime. Trace element fertilisers are applied by spreading small amounts of chemicals. It is usually easier to do this if the chemical is first dissolved in water and then sprayed over the soil or pasture.
Blood and bone fertiliser contains nitrogen and phosphorus in varying amounts according to the material used to produce it. Dried blood is another organic fertiliser and it supplies nitrogen to plants slowly.
Bone dust is made from crushed bones and it supplies phosphorus but also a little nitrogen. These nutrients are slowly available. Nearly all Australian soils are deficient in phosphorus, and it is usual to drill in superphosphate when the seed is sown. In some high rainfall areas potassium is washed out of the soil and must be added. Root crops like turnips use a lot of potassium, and several crops may exhaust the soil of this nutrient.
The nutrient which is of the greatest importance to crops of the grass family, and too many others, is nitrogen. In fact, nitrogen is so important to crops like sugar cane, maize and broom millet that high yields cannot be obtained without it.
The importance of nitrogen is clear from the table below, which shows the improvement in average hectare yields of three important crops in the USA. These remarkable increases have followed the greater use of nitrogenous fertilisers which became cheaper at that time.
There are two ways of building up supplies of soil nitrogen. The simplest way is to add to the soil a chemical fertiliser containing nitrogen such as the substance urea. The high cost of nitrogenous fertilisers is the only reason they have not been used extensively in the past.
Another method of increasing soil nitrogen is to grow crops of legumes like cowpeas or velvet beans, that are rich in nitrogen, and then to plough these crops into the soil while they are in the actively growing stage. Pasture legumes like white clover also build up supplies of nitrogen in the soil, and this nitrogen is then available for crops to use.
The increased yields of wheat in Australia have been largely due to wheat being planted on soils enriched by the growth of pasture legumes. If soils are deficient in any other nutrient, these must be added. For instance, many soils of the north of New South Wales are deficient in sulphur. This is corrected by adding superphosphate (which contains calcium sulphate) or by adding gypsum or flowers of sulphur.
Factor # 4. Crop Enemies:
High yields are impossible unless crops are protected from insect pests, diseases and weeds.
Most insect pests do not attack a plant until it is well grown. Insects such as caterpillars and grasshoppers eat the leaves; other insects, such as the green vegetable bug, suck out the plant juices through a fine mouth tube. To kill leaf-eating insects it is usual to spray the leaves with stomach poisons like lead arsenate. But these stomach poisons will not kill the sucking insects, which must be attacked by using contact poisons like Maldison, Endosulphan, Methyl-parathion and the miscible oils.
Plant diseases may be caused by fungi, viruses or bacteria. Fungi are microscopic plants which lack chlorophyll. They cannot manufacture their own food, and therefore are only found living on the ready-made food in the bodies of dead or living organisms. All fungi begin their life cycle as a single microscopic spore which can be blown about by the wind.
If a spore is blown onto a healthy plant, it may germinate and form tiny white branching threads such as are seen growing on mouldy oranges or mouldy bread. This is the body of the fungus, and when mature it makes millions of spores which can infect other plants. Plant disease fungi are of two chief kinds.
Some, like the powdery mildews of pumpkins and wheat, only live on the outside of plants. Because they stay on the outside, they are easily killed by spraying the leaves with Bordeaux mixture or flowers of sulphur.
The more serious disease-causing fungi are those which live inside a plant. Once these parasites enter the plant body, there is nothing we can do to kill them without killing the plant too. Therefore to stop these diseases, we must either spray the plant with some fungicide like Bordeaux mixture before the spores enter, or we must use only the varieties which are resistant to these diseases. The worst internal fungus diseases are the rusts, and diseases like downy mildew of grapes, blue mould of tobacco, the late blight of potatoes and boil smut of maize.
Viruses are particles so small that we cannot see them even when we use the highest-powered microscopes. These particles are usually carried to healthy plants on the mouthparts of insects. The signs of virus diseases vary a good deal, but common signs are the mottling appearance of the mosaic diseases, and the bunched appearance of the leaves in the rosette diseases.
Virus diseases may be controlled in three ways. We should first see to it that we choose seed which is free of virus infection. In some cases it is possible to buy seed of varieties which are resistant to virus diseases. Since viruses are usually carried by insects, we can control the disease by controlling the insect that carries it.
Bunchy top of bananas, potato leaf curl, and bronzy wilt of tomatoes are important virus diseases, and it appears that virus diseases of grass plants have now appeared in Australia.
Bacteria are very like fungi except that they are smaller and consist of single cells. The disease-causing bacteria, such as those causing black rot of cabbages, always live inside the plant body. The best control is to buy good seed, or seed of varieties which are resistant to bacterial attack.
Undoubtedly the worst enemies of many crops are the weeds which grow up with them. Weeds may compete with crop plants for light, water and nutrients, and they always have an effect on yield. Weeds may result in a slight reduction in the yield of a crop, or they may so reduce the yield that it is not worthwhile trying to harvest the crop.
Some, like skeleton weed, may grow into such a thick tangled mass that the harvesting machinery cannot move properly through the crop. In some cases the weed seeds are harvested with the crop grain and they reduce the value of the grain. It may be necessary to put all the grain through a grading machine to remove the weed seeds.
Factor # 5. Management:
There are so many ways in which management of a crop can affect the yield, that we can only mention each one briefly. No crop will grow well unless it gets a good start in a suitable seed bed. The seed bed must either be fine or coarse, it must have fine soil down at the depth where the seed is to be sown, and it must be moist. Different crops need quite different seed beds, and there is much to learn about this.
Sowing a crop must be done well. The seed must be drilled in at the right depth, depending on the size of the seed and the season. Generally the smaller the seed the closer it must be sown to the surface. In a dry autumn wheat farmers may drill the seed in at a shallower depth than usual.
If sown at the usual depth, there may be just enough moisture to soften the seed but not enough to germinate it properly and the grain may then rot in the ground or “malt” as it is called. The time of sowing will depend on the growing season of the variety which has been chosen and on taking advantage of recent or expected rains.
One of the most important decisions a farmer must make at sowing time is the sowing rate—the density of plants which he wishes the crop to have. From our study of competition we can understand that the sowing rate must be lower in dry districts, for if not, each plant will compete strongly with its neighbour for soil water.
Similarly we can understand that the rate may be increased if the soil is rich in nutrients. The study of competition also makes it plain that the rate of sowing affects grain production, for if the sowing is too thick, grain production will be lowered. But it is also known that the maximum production of grain is obtained when the sowing rate is so high that the production of each plant is slightly deduced by the competition.
The proper cultivation of a crop is often essential if top yields are desired, and the chief reason for cultivating a crop is to kill out weeds when they are young.
Harvesting a crop must be done well, and must be timed properly. Crops harvested for silage must be cut when they are of large bulk and still succulent. Crops being turned into hay are usually cut before they set seed, although some buyers like some grain in oaten hay. Grain crops must not be harvested until the grain is mature, and hot dry weather is usually the best for grain harvests.
Grain or hay which is to be stored must be protected from rain, fire, and from insects and animals. Hay sheds and grain silos must be placed on gently sloping land above flood levels, and be built of proper materials.
Some farmers fail to receive a high price because they do not send their product to market in the proper condition. Great care should be taken to clean vegetables and prepare them properly for market. Fruit should be graded for size and well packed in boxes. Products like peanuts and potatoes gain a better price if they are cleaned and graded before sale.
Another aspect of management is the efficient use of machinery. First the farmer must know a lot about the different kinds of machines and he must buy what will suit his purpose best. He must have enough machinery to do what he thinks is best for the crop, but he must not buy too much machinery, or buy an expensive machine when a cheaper one would do. Machinery must not be allowed to wear out too soon, and this can be prevented by regular lubrication and protection from the weather.
Only when a farmer has followed all these steps in management can he feel confident that nothing but a storm or a drought will prevent him from obtaining high yields from his crop.