CONTENTS xiii 



FACTORS DETERMINING SOIL FERTILITY 



VIII. SOIL WATER AND ITS RELATION TO SOIL FERTILITY 89 



1. Why Plants Require Water. 2. Crops Require Much 

 Water. 3. Water Requirements of Some Crops Based on 

 Dry Matter Produced. 4. Water Commonly Limits Crop 

 Production. 5. Forms of Soil Water Gravitational, Capil- 

 lary and Hygroscopic. 6. Capillary Water of Most Import- 

 ance: Held by soils in form of films around the soil particles, 

 in organic matter, and within soil crumbs. 7. Movements 

 of Water in Soils: Percolation, seepage, capillary rise of 

 water. 8. Water-holding Capacity of Soils. 9. Moisture . 

 Conservation and Control (a) Lessen surface run-off by 

 aiding soils to trap water. (fr) Increase water-holding 

 capacity by adding organic matter, (c) Aid capillary rise of 

 moisture by compacting the seed bed. (d) Lessen surface 

 evaporation by developing a soil mulch, (e) Conserve mois- 

 ture by killing weeds. 



IX. LAND DRAINAGE AND IRRIGATION 109 



1. Too Much Water is Harmful. 2. Benefits of Proper 

 Drainage. 3. How Drainage is Accomplished: (a) Surface 

 drainage. (6) Subsurface drainage, (c) Vertical drainage. 

 (d) Combined methods. 4. Tile Drainage: (a) Drain tile 

 and how they are laid. (&) Distance to lay lines of tile, (c) 

 Systems of tile drainage natural, gridiron, herring-bone 

 and combination of systems, (d) Cost and benefits of tile 

 drainage. 5. Drainage by Means of Pumps. 6. Irrigation 

 Defined : (a) Objects of irrigation and how irrigation water 

 is secured. (6) How irrigation water is applied flooding, 

 furrow irrigation, spray irrigation and sub-irrigation, (c) 

 Irrigated farms require good management. (d) Many 

 irrigated lands need drainage, (e) Profits in irrigation 

 farming. (/) Irrigation an art of antiquity. 



X. TILTH AND TILLAGE 135 



1. Tilth and Tillage in General: (a) Factors determining 

 development of good tilth. (6) Tillage tools are many, (c) 

 Objects and principles governing tillage. 2. Preparing the 

 Seed Bed: (a) Plows and plowing, (fr) Subsoiling, deep till- 

 ing and dynamiting soils, (c) Harrows and harrowing, (d) 

 Rollers, plankers and clod crushers. 3. Seeding and Plant- 

 ing: (a) Good firm seed bed favors planting. (6) Drills vs. 

 broadcast grain seeders, (c) When discing is better than 

 plowing. (d) Listing. 4. Cultivation and Intertillage : 

 (a) Why crops are cultivated. (6) Cultivators and their 

 adaptability, (c) When and how to cultivate. 



XI. SOIL ORGANISMS IN RELATION TO SOIL FERTILITY 171 



1. Organisms of Decomposition: (a) No crops without de- 

 cay. (6) Organisms cause decay of organic matter, (c) Decay 

 of organic matter aids decay of mineral particles, (d) Some 

 fertilizers would be valueless without decay. 2. Bacteria 

 Which Cause Nitrification: (a) Importance of nitrification. 

 (6) Catch and cover crops conserve nitrates, (c) Nitrifica- 

 tion results in loss of organic matter. 3. Bacteria which Fix 

 Atmospheric Nitrogen in Soils: (a) Two groups of nitrogen- 

 fixing bacteria. (6) Amount of nitrogen gathered per acre, 

 (c) How nodule bacteria work, (d) How the growing of 

 legumes improves soils, (e) Soil inoculation and methods. 

 (f) Conditions favoring soil bacteria. 



