BC1 FRONT COVER REV2.indd

B et te r C ro ps /V ol . 9 9 (2 01 5, N o. 1 ) Abbreviations and notes: N = nitrogen; P = phosphorus; K = potassium; S = sulfur; Cu = copper; Fe = iron; Mn = manganese; Mo = molybdenum; Zn = zinc. Sustainable crop production is essential to a healthy and adequate food supply. At fi rst glance, a healthy crop reveals only the above ground plant; the roots that support the visible plant are seldom seen. But these plant roots grow in an incredibly complex environment, teeming with billions of soil organisms, particularly bacteria and fungi, which play a crucial role in promoting root health and maintaining an adequate supply of plant nutrients for crop growth. There is still much to learn about the complex interaction between soil microorganisms and plant nutrition, but the importance of these relationships are now clearly recognized. Only a few of the key interactions between soil microbes and plant nutrition can be discussed in this brief summary. It has long been observed that plants conspicuously modify their soil environment by exuding large amounts of carbon from their roots. This rhizosphere zone becomes a biological hotspot in the soil. Adding carbon to the soil surrounding the roots leads to a huge increase in the number of microorganisms living within and outside the roots. These root exudates are composed of a complex mixture of low-molecular weight compounds such as amino acids, organic acids, sugars, and phenolics. Root mucilage, a carbon-rich gel layer surrounding the root tip, also provides a complex mixture of sugars, proteins, and enzymes to rhizosphere organisms. In some plants, as much as one-third to one-half of all the total carbon assimilated by photosynthesis can be transferred to the soil through the roots (Kuzyakov and Domanski, 2000). As soluble carbon is released by roots, microorganisms are stimulated and colonize the soil surrounding the roots. This can result in competition for nutrients because plants and microbes rely on the same essential nutrients for growth.