Texts for supplementary reading. Crop Production, as a Science

Agronomy is the branch of agriculture that treats of the principles and practices of crop production and field management.

The term was derived from two Greek words agros (field) and nomos (to manage). Agronomy has been a distinct and recognized branch of agricultural science only since about 1900. The American Society of Agronomy was organized in 1908. Agronomy had its origin largely in Sciences of Botany, Chemistry and Physics. Prior to the early years of the present century, crop experiments usually were trained by botanists, chemists, or general agriculturists, or by interested farmers, gardeners, or naturalists who became agronomists by adoption. Thus a new science of agronomy was built up by coordination of knowledge derived from the natural and biological sciences with the written records of observations and empirical trials, and later of controlled experiments dealing with crop production.

Better crop production follows application of new discoveries, adoption of improved machines, and breeding of new crop varieties.

Origin of Cultivated Plants

All basic cultivated food plants are believed to have been derived from wild species. But they have undergone extensive modifications from their wild prototypes as a result of the continuous efforts of man to improve them.

The differences between cultivated and wild forms are largely in their increased usefulness to man, due to such factors as yield, quality and reduced shattering of seed. Crop plants may be classified on the basis of a morphological similarity of plant parts. From the agronomic standpoint they may be classified on the basis of use, but some crops have several different uses.

What Plants Eat and What Chemistry Has to Do with It

It would seem that plants were not very particular about their food. Herbs and bushes have survived in hot desert and in the polar tundra. They may be stunted and wretched to look at, but they have survived.

There was something they needed for their development, but what? Scientists sought this mysterious "something" for many years.

Despite all their experiments, in spite of all their discussions nothing definite was found.

The answer was finally supplied in the middle of the last century. The chemical analysis of a great variety of plants showed the latter "to be composed" of a number of separate chemical elements. At the onset there were not so many of them, ten in all: carbon and hydrogen, oxygen and nitrogen, calcium and potassium, phosphorus and sulphur, magnesium and iron. But these ten elements gave rise to the vast ocean of foliage on the Earth. It followed therefore that for plants to stay alive they had somehow to assimilate to "eat" these elements.

But how? Where are the food stores of plants?

Obviously, in the soil, in the water, and in the air. There were some strange things, however, that had to be explained. In some soils a plant might develop rapidly, blossom and bear fruit, whereas in others it would droop, wither and turn into a sickly freak. Evidently the latter soils lacked some elements.

It was known long before that if the same agricultural crops were sown year after year on even the most fertile soil, harvests would become worse and worse.

The soil became impoverished. The plants gradually “ate up” all the chemical elements in it that they needed.

The soil had to be “fed’’, that is, the supply of substances removed from it had to be replenished. In other words, it had to be fertilized, as we usually say. Fertilizers were used way back in distant antiquity. They were introduced into the soil intuitively, on the basis of experience handed down from generation to generation. Now the use of fertilizers has been raised to the rank of a science and this science is named agrochemistry. Chemistry became servant to plant growing. It teaches people the right way to use known fertilizers and invent new ones.

Dozen of different fertilizers are known today. The most important of them is potassium, nitrogenous and phosphate fertilizers, because potassium, nitrogen and phosphorus are the elements without which not a single plant can grow.

Weeds

A weed may be defined as a plant growing where it is not wanted.Weeds in field crops are harmful for a variety of reasons. They reduce the yields of crops as well as their quality. There are weeds, which are known to be poisonous both to livestock and men. Some weed species serve as host plants for certain insects and diseases that attack crops, they may thus act as sources of infection for farm crops.

Weeds deprive the crop of water, mineral nutrients and light, which would otherwise be available and so prevent it from producing high yields. The extent to which yields may be reduced as a result of competition caused by weeds varies greatly. It depends on the competitive ability of the crop grown, on the type of weeds present and on the season the crop is sown or planted at. There exist different methods of controlling weeds in farm crops. The oldest but still common method is early and frequent cultivation of the land with different types of cultivators. These implements can be used in weedy fields of row crops such as corn, potatoes, soybeans, sugar beets and beans. Crop rotation is also very useful in destroying weeds since many of them are associated with certain crops. That is why the number of weeds increases, provided a crop is continuously grown on the

same land. The control of weeds through the use of chemical herbicides has expanded considerably. For a herbicide to be effective it should be used at a certain stage of crop growth when it produces the least or no injury to the crop, the rate and method of applying herbicide being of great importance as well.