Trace elements in soils and agriculture [antikvár]

- 1 - I. iirraoDUCTioii To weet the demand of the rapidly increasing population of the world, «ore and more food and fibre must be produced from each hectare of the world's arable land. Modern cultivation methods, improved varieties, better control of plant diseases, pests and weeds and increasing use of mineral fertilizers, increase in irrigated area, etc. are factors responsible for the general increase in crop yields in recent decades and years (Table 1). Table 1. Development of world werage yields of nine commonly grown crops and consumption of three main fertiliier nutrients (120). Periods 1948-52 1952-56 1963-67 Crop lilograms per hectare Wheat 990 1 080 1 280 Rice 1 630 1 820 2 070 Maize 1 590 1 700 2 280 Millet & Sorghum 510 560 740 Barley 1 130 1 250 1 560 Oats 1 140 1 190 1 530 Soybeans 1 000 980 1 180 Cottonseed 440 500 630 Potatoes 10 900 11 100 12 600 nutrient Kilograns per arable hectare H 3 4 12 P205 4 5 10 IjO 3 4 8 In spite of the favourable development in fertilizer use, two to six times more of the main nutrients are still renoved annually from the soil than are applied to it as mineral fertilizers. Some of the removed nutrients are replaced by those in straw, farmyard manure, etc.but on average the nutrient balance is likely to remedn negative. Trace elements are not regularly applied to soil by the use of the common fertilizers. Their rooval from the soil has been going on for centuries without any systematic replacement. Trace element deficiency cases were first reported at the end of 19th century and today it it known that extensive areas of our soils are incapable of supplying plants with sufficient aiKiunts of micronutrients. The one-sided development in the fertilizing of soils with only main nutrients stimulating increased yields, the loss of trace elements through weathering and leaching, the decreasing proportion of farmyard manure and other natural fertilizer materials used in caqiarison with chemical fertilizers, the increasing purity of chemical fertilizer materials and several other factors is contributing toward accelerated exhaustion of the available supply of trace elements in soils. Around nine tenths of a fresh plant consists of water, and about 9S percent of the rcMdning dry matter of most plants is oovosed of four elcunts: carbon, hydrogen, oxjrgtn and aitrogcD. Potassius, phosphenia, calcium, magnesium. sUicon, aluminium, sulphur, chlorinc and sodium cospose about four percent of the dry weight and the remaining one percent or less is accounted for by another dozen or more elements including all the essential micronutrients.