Advances in agriculture last century enabled global food production to keep up with a near fourfold increase in human population. From the 1950s, arable land for agriculture barely increased, making this scientic feat even more impressive (Evans 1993). Many improvements involved soil management, and thus indirectly the roots of new varieties empirically selected by breeders on yield alone. Examples from Australian wheat cropping systems include the addition of phosphorus fertilizer early in the century, addition of lime and manganese to support nitrogen xation by legumes in acidic soils mid-century, rotations with canola and legumes to break root disease cycles and allow response to nitrogen application in the 1980s, and the widespread adoption of zero tillage late in the century which probably enabled survival of farms through the millennium drought at the turn of this century (Angus 2001; Kirkegaard and Hunt 2010). Global food production must double again over the next 100 years to meet population growth and growing auence and diet shis toward meat in the most populous countries, China and India. In the case of cereals, which provide over half the calories to humans, this can be achieved without an increase in food price if the yield of crops increases annually by about 1.5% (50% faster than the current rate), and this yield is reached with less water, less fertilizer, and less fertile land for agriculture (Fischer and Edmeades 2010). erefore, productivity (production per land area per resource input) must increase. Here we address this challenge in terms of opportunities from the genetic improvement and agronomic management of roots using ideotypes or traits suited to environments or farming

systems (Figure 21.1). We bias our examples from the literature on evaluations in soil in controlled conditions or in the eld in farming systems. e scope of the review is crop root systems that have a role in water and nutrient uptake, anchorage and soil amendment, but are not harvested for food. Root crops are covered in Chapter 30.