III. Determine in the sentence the verb expressing the obligation. Translate the sentences.

1. Where erosion will not be too serious, the meadow should be plowed after the last hay crop is removed.

2. On many soils, although high in total nitrogen, extra fertilizer nitrogen must be added to the soil in order to raise satisfactory yields.

3. Soil reaction should be considered when growing plants.

4. The optimum fertilizer rate must be determined anew each year.

5. The study of the balance of plant nutrients in the soil and the study of crop yields should be closely connected.

6. Some heavy fertilized crops must be fertilized almost at any price if their culture is to continue.

7. Some workers consider that the total quantity of lime in a soil should be considered in recommending lime applications.

8. Fertilizers have to be placed into the soil in such a way that they are close to the seed but do not injure it.

9. Some kind of investigation has to be made or nitrogen and phosphoric acid when applied separately, and in various kinds of fertilizers.

10. Any drain that is to operate efficiently must be kept clean.

11. Trenches should be filled soon after the tiles are laid.

12. Peat land should not be confused with muck.

13. Before the organic matter is effective as an aggregating agent, it must be decomposed.

14. The weeds should be killed before they produce seed.

15. If we are to meet these new demands for farm produce more efficient use must be made both our land and water.

16. Where large fields are to be contour-farmed, contour lines should be laid out at normal strip intervals.

17. On sloping land soil and water losses are to be reduced to a minimum.

18. The surface of the ground must be protected from the bad effects of erosion at all times.

IV. Find the Present Participle in sentences, define its function. Translate the sentences

1. The colloidal constituents of the soil are the seat of the most of the chemical and physical reactions taking place in the soil.

2. Organic matter decaying in the soil loses its basic constituents.

3. Both the active and reserve acidity must be included when considering the total soil acidity.

4. Working with small grains of the grass family it is customary to sample the stems, but not the leaves themselves.

5. Beginning in 1911 intensive studies of rotations were conducted on the experimental farms throughout Canada.

6. Urea is increasing in importance, but is not yet a major fertilizer.

7. Acid soils have been found to contain varying quantities of soluble aluminum.

8. The quantities of different liming materials to be applied depend on many factors.

9. Any factor that decreases the rate of respiration of growing pant roots decreases the nutrient absorption.

10. Falling raindrops have great capacity to damage soil.

11. Maximum erosion occurs when the detaching and transporting capacities of surface flow are balanced.

12. Soils having low resistance to the raindrop impact usually require more intensive protective measures that those possessing high resistance.

13. Soils vary considerably in their resistance to wind erosion, depending generally on the size of the particles and content of the organic matter.

14. Flowing surface water is usually the major transporting agent of the soil when erosion is caused by rainstorm.

15. Both science and practice of using commercial fertilizers are undergoing radical changes.