xii CONTENTS 



CHAPTER PAGE 



matter in soils in cool, moist regions, (d) Deficient organic 



matter in soils in warm, moist regions, (e) Sour or acid soils 

 found in humid regions. 



SOIL AND PLANT RELATIONS 



V. SOIL AN IMPORTANT FACTOR AFFECTING PLANT GROWTH 47 



1. Conditions Surrounding Plants Must be Favorable. 



2. Three Periods of Life History of Plant Passed in Contact 

 with the Soil. 3. The Germination Period : (a) Life in seed 

 strives for existence. (6) Requirements moisture, oxygen, 

 favorable temperature and good tilth, (c) Tilth, good tilth, 

 poor tilth defined, (d) Absorption of water by seeds influ- 

 enced by contact between soil and seed, moisture, warmth 

 and presence of salts. 4. The Vegetative or Growing Period : 

 (a) Period of greatest activity. (6) Conditions and require- 

 ments, (c) Full meaning and importance of good tilth, 

 factors affecting development, (d) Availability of plant-food 

 elements, (e) Special function of the plant-food elements. 

 5. The Fruition Period. 



VI. CROPS AS FEEDERS ON THE PLANT-FOOD ELEMENTS IN THE SOIL 61 

 1. Soil Particles are not Plant Foods. 2. Amount of Ele- 

 ments Removed by Harvested Crops. 3. Some Facts Con- 

 cerning the Feeding of Crops: (a) Most of phosphorus goes 

 into grain, and potassium into stalk and straw. (6) All 

 plants do not take the same amounts of the elements, (c) 

 Alfalfa a " heavy feeder." (d) Timothy is not a "soil rob- 

 ber." (e} Some plants have strong feeding powers. (/) 

 Barley requires a richer soil than oats. (#) Fertilizer needs 

 best determined by tests. 4. Amount of Plant-food Ele- 

 ments Removed by Fruit Crops. 5. Supply of Nitrogen, 

 Phosphorus and Potassium in Soils: (a) Supply varies in 

 different soils. (6) Per cent vs. pounds of plant-food ele- 

 ments in soils, (c) Peat soils are usually deficient in the 

 mineral elements (K and P). (d) Peat lands are sometimes 

 deceptively advertised. (e) Subsoils contain plant-food 

 elements. 



CROP PRODUCTION 



VII. CROP PRODUCTION AND SOIL FERTILITY 75 



1. Factors in Successful Crop Production: (a) Fertile soil, 

 determined by moisture in soil, air in soil, good tilth, pres- 

 ence of helpful organisms, plant-food elements, absence of 

 harmful agents. (6) Good seed: high test, adaptability, 

 purity, disease resistant, high yielding, etc. (c) Favorable 

 temperature, (d) Light: some crops require much light, 

 some less; shading a factor in weed-killing; weeds may shade 

 crops; one crop may deprive another of light, (e) Protection 

 from injury: proper fencing, spraying, treating seed, drain- 

 age, etc. 2. Soil Fertility (Defined). 3. Factors which 

 Determine Soil Fertility Same as Those Which Make a Fertile 

 Soil. 4. Soil Exhaustion: (a) Illustrated by draft upon the 

 phosphorus supply. (6) Soil exhaustion usually the result 

 of: the removal of organic matter; the removal of available 

 plant-food elements; the removal of carbonate of lime; 

 improper tillage. 5. Most Soils can be Improved in 

 Some Way. 



