The soil is the store of water and nutrients for most plants and living organisms on land (Noy-Meir, 1973), and acts as an important hydrologic “valve” for the partitioning of the land-surface water and energy fluxes. While soil is often idealized as a mixture of mineral, liquid, and gaseous components, it is in reality a very complex biomaterial (Brady and Weil, 1996; Richter and Markewitz, 2001; Paul, 2006), which provides different environments for plants and microbial life. Owing to this complexity, there are several ways in which soils have been classified and analyzed.

In this section, we review some concepts needed to define water potential and describe water status within the soil–plant–atmosphere continuum, which will be important in Chapters 3–5. More in-depth descriptions of thermodynamics can be found in the following excellent books: Kestin (1979), Zemansky and Dittman (1997). Kondepudi and Prigogine (2005), Bejan (2006), and Callen (2006).

Thermodynamics is founded on two main laws, which are complementary to the mass and momentum conservation equations. They describe how energy is distributed among its different forms, transferred, and degraded during thermodynamic transformations. These laws may be applied to systems that are isolated, i.e., in which there is no exchange of energy or matter, or closed, i.e., which do not allow mass exchange but do allow energy exchange, or open, i.e., where both mass and energy exchange with the surroundings are possible.

Ecohydrology is the study of the two-way interaction between the hydrological cycle and ecosystems. More broadly, it is the science of the linkages between life and water on Earth. On the one hand, the space and time variability of the hydrological cycle controls the water availability for ecosystems; on the other hand, ecosystems, especially through transpiration by vegetation, control the main pathway by which water returns to the atmosphere from land. The terrestrial water cycle also drives some of the dynamics of soil organic matter (SOM), microbial biomass, and the related nutrient cycling. These in turn not only affect the vegetation dynamics but also impact the hydraulic and thermodynamic properties of soil, thereby directly acting on the partitioning of water and energy fluxes at the land–atmosphere interface.

In water-controlled ecosystems, water demand by plants is generally higher than water availability, leading to plant water stress. To cope efficiently with water stress, plants have developed different strategies, which become more sophisticated the more intense and unpredictable the water deficit is. Many species combine a number of complementary measures to develop such strategies, the most extreme of which include permanent forms of adaptation, such as changes in resource allocation, specialized root growth (e.g., cacti build a dense network of roots to capture light rainfall events, while some desert shrubs - the so- called phreatophytes – develop deep roots to tap the water table when present), specialized photosynthetic pathways (e.g., the CAM pathway), short and intense life cycles during favorable periods, dormancy, drought deciduousness, specialized metabolism and leaf structure to reduce water losses (high cuticular resistance, protection and changes in dimension and density of the stomata), etc.

Plant physiologists usually distinguish two kinds of water in vascular plants: apoplastic water, located outside the plasma membranes and relatively free to move from roots to leaves through the xylem conduits, and symplastic water, which is contained in the protoplast of the living cells (see Fig. 4.1). We discuss here only the main issues related to modeling water transport and refer to specialized books for more details on plant physiology and ecology (e.g., Salisbury and Ross, 1969; Jones, 1992; Lambers et al., 1998; Nobel, 1999; Larcher, 2003).

The dynamics of soil carbon and nitrogen are extremely important for the life and growth of vegetation and have impacts on climate and several soil processes. Hydrological fluctuations play an important role in modulating the speed of these cycles, from the microbial decomposition of organic matter and the related soil respiration and nitrogen mineralization to nitrogen uptake by plants and leaching to groundwater and streams. By enhancing some processes and quenching others, the patterns of soil moisture regulate the sequence of fluxes between different components and determine the dynamics of the other state variables of the system. Plants are often both water and nutrient limited, so it is difficult to determine the extent to which net primary production is controlled by water or nutrient availability. As noticed by Pastor et al. (1984), the nitrogen cycle needs to be explained through the water balance; not less marked is how the soil water balance controls the carbon cycle.

In Chapters 3–5 we described the temporal evolution of the main ecohydrological processes within the soil–plant–atmosphere continuum, in the absence of rainfall variability. Starting from a finer timescale description, where the fastest processes resolved are on the order of tens of minutes, we obtained a representation of the water, energy, and carbon fluxes at the daily level (see Sec. 5.4.5), expressed as a function of mean daily soil moisture and atmospheric characteristics. In Chapter 6 we introduced the probabilistic tools necessary to account for the fact that the forcing terms, rainfall in particular, are highly unpredictable at longer timescales. In this chapter, we finally combine these concepts to arrive at a stochastic description of soil moisture dynamics.

It is true that most teachers have limited knowledge of how words work in English. Linguistics hasn’t been a feature of their own schooling or their teacher education, and you can’t teach what you don’t know. The good news is that it isn’t hard to build the knowledge – in fact, it’s fun. In this chapter we look more closely at the linguistic threads that contribute to the rich tapestry of each word: etymology, orthography, phonology and morphology.

Chapter 3 outlined four key principles for teaching spelling: start with meaning; teach spelling explicitly; teach a repertoire of spelling knowledge; and integrate spelling instruction into all subject areas. This chapter introduces a 10-step process for planning and implementing a spelling program that is grounded in those four principles. Interspersed among the steps in the planning process are some of the questions teachers and parents frequently ask as they embark on the implementation process. What would your answers be? My responses are posted at the end of the chapter.

This chapter is focused on getting spelling assessment right, and expands upon steps 9 and 10 in the program planning process, introduced in chapter 4: assessing spelling in use, and keeping records of teaching and learning.

In this introductory chapter, fragments from the spelling stories of children, teachers, parents and carers will be used to paint a broad picture of what spelling is and what it isn’t. The following chapters provide more detailed guidance on how to work with children to build their spelling skills in productive ways.