Principles of Soil and Plant Water Relations

M.B. Kirkham

• Publisher: Academic Press
• Year: 2014
• ISBN:
  9780124200784
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Botany
• Index: Biological Sciences

Principles of Soil and Plant Water Relations, 2e describes the principles of water relations within soils, followed by the uptake of water and its subsequent movement throughout and from the plant body. This is presented as a progressive series of physical and biological interrelations, even though each topic is treated in detail on its own. The book also describes equipment used to measure water in the soil-plant-atmosphere system. At the end of each chapter is a biography of a scientist whose principles are discussed in the chapter. In addition to new information on the concept of celestial time, this new edition also includes new chapters on methods to determine sap flow in plants dual-probe heat-pulse technique to monitor water in the root zone.

• Provides the necessary understanding to address advancing problems in water availability for meeting ecological requirements at local, regional and global scales
• Covers plant anatomy: an essential component to understanding soil and plant water relations

Chapter 1

Introduction

Abstract

This chapter tells why it is important to study soil–plant–water relations. Water is the most important substance necessary for food production. People depend upon plants for food, so the challenge of feeding a growing population is discussed. The human population growth curve, a logarithmic one, is presented. Rules of logarithms are then given. A calculation is done to show that the human population is limited by the productivity of the land. The calculation shows that it requires two square yards (16,700 cm²) to feed one person. The sigmoid plant growth curve is presented followed by a mathematical analysis of Blackman's compound interest law for plant growth. Finally, data from corn and soybean are analyzed to show that their growth rate is exponential. A biography of Napier, the inventor of logarithms, is given in the appendix.

Keywords

Blackman growth curve; John Napier; Logarithms; Population curve; Sigmoid growth curve; Soil–plant–water relations

1.1. Why Study Soil–Plant–Water Relations?

1.1.1. Population

Of the four soil physical factors that affect plant growth (mechanical impedance, water, aeration, and temperature) (Shaw, 1952; Kirkham, 1973), water is the most important. A classic analysis was done by Boyer (1982) to determine the reasons for crop losses over a four-decade period in the United States. He found that drought causes 40.8% of crop losses and excess water causes 16.4%. Insects and diseases amount to 7.2% of the losses. Thus, soils that are too dry or too wet are the major reasons for lost productivity.

People depend upon plants for food. Because water is the major environmental factor limiting plant growth, we need to study soil–plant–water relations to provide food for a growing population. What is our challenge?

The earth's population is growing exponentially. The universe is now considered to be 13,000,000,000 (13 thousand millions or 13 billion) years old (Zimmer, 2001). The earth is thought to be 4.45 billion years old (Allègre and Schneider, 1994). The earth's oldest rock is 4.03 billion years old (Zimmer, 2001). Primitive life existed on earth 3.7 billion years ago, according to scientists studying ancient rock formations harboring living cells (Simpson, 2003). Human-like animals have existed on earth only in the last few (less than 8) million years. In Chad, Central Africa, six hominid specimens, including a nearly complete cranium and fragmentary lower jaws, have been found that are 6–7 million years old (Brunet et al., 2002; Wood, 2002). The earliest fossil in Europe, which belongs to the genus Homo, was found in Spain and has been dated to 1.1–1.2 million years ago, which suggests that the first settlement of Western Europe was related to demographic expansion out of Africa (Carbonell et al., 2008).

In 8000 BC, at the dawn of agriculture, the world's population was 5 million (Wilford, 1982). At the birth of Christ in 1 A.D., it was 200 million. In 1000, the population was 250 million (National Geographic, 1998a) (Figure 1.1). By 1300, it had grown larger (Wilford, 1982). But by 1400, the population had dropped dramatically due to the Black Death, also called the bubonic plague (McEvedy, 1988), which is caused by a bacillus spread by fleas on rats. The Black Death raged in Europe between 1347 and 1351 and killed at least half of its population. It caused the depopulation or total disappearance of about 1000 villages. Starting ...