ABSTRACT
As we noted in Chapter 1, the four soil physical factors that affect root growth, and consequently plant growth, are water, aeration, temperature, and mechanical impedance (Kirkham 2005, p. 1). In Chapter 1, we looked at the effect of lack of water on plants under elevated atmospheric CO2. In this chapter, we turn to soil aeration and focus on elevated CO2 in the soil atmosphere. Most biological reactions that occur in soil consume oxygen (O2) and produce CO2. The effects of soil aeration on growth of plants can be divided into two categories (Taylor and Ashcroft 1972, p. 352). First, reduction of soil constituents occurs, which in turn in®uences growth. In the absence of adequate O2 in the soil, sul£de, ferrous, and manganous compounds form; organic matter is reduced to alcohols, aldehydes, or methane, and hydrogen gas may appear; and essential nitrates are reduced to toxic nitrites or to free nitrogen gas (Taylor and Ashcroft 1972, p. 352). We shall not be concerned about these soil processes in this chapter. Second, aeration directly affects the physiological condition of plants. They require adequate soil aeration for the proper development of their root systems. Because the greatest in®uence of aeration on root growth is attributable to the concentrations of O2 and CO2 in the soil air (Taylor and Ashcroft 1972, p. 353), we shall consider both gases in this chapter.
