By: Jerry L. Hatfield, Laboratory Director, National Laboratory for Agriculture and the Environment
Getting Into Soil & Water 2012
There is a continual dialog about the food required to feed a population of nine billion people by 2050 and the changing climate and the impacts on food production and food security. In all of this discussion there is little attention given to the fundamental fact that without soil we would produce little food. There is also little notice given to the fact that the land area we will have available to produce this food will continue to decline as the population increases. Another fact which can’t be ignored is that our soils continue to be degraded, thereby losing their ability to supply water and nutrients to plants.
If we examine a very simple concept of water use efficiency as shown on the attached diagram then we observe that the more water transpired by the plant, the higher the grain yield. As we limit water, we limit plant productivity and with the more variable rainfall expected under climate change then we can expect more variation in crop production. Across the Midwest, the primary factor causing yield variation among years is rainfall and within fields is the ability of the soil to supply adequate soil water during the grain-filling period. As an example of this dilemma, when we couple the water use efficiency concept with the desire to produce more corn, a simple extrapolation to achieve 18,900 kg/ha (300 bu/A) of corn from our present levels will require another 200 mm (7.8 inches) of water transpired through the plant. Soil is a water reservoir and the degradation process reduces the ability of the soil to store water because of the loss of organic carbon content and subjects the soil to crusting and erosion leading to less water being infiltrated into the soil. If we have more variable rainfall and a diminished capacity to infiltrate or store soil water then it may be difficult to achieve the yield increases required to adequately feed the world’s population.
Soil degradation occurs through physical, chemical, and biological changes. Two agronomic components are always mentioned with soil degradation; increased tillage and residue removal. The physical processes associated with degradation include the loss of soil structure, crusting, compaction, erosion while chemical degradation is linked with nutrient depletion, elemental imbalance, acidification, and salinization, while biological degradation is caused by depletion of soil organic matter and reduction in the diversity and activity of soil microorganisms. Any change in the soil will begin the process of degradation and limit its ability to supply water and nutrients to plants. However, we assume that we can overcome these problems with the addition of nutrients to the soil and supplying water through irrigation. Unfortunately, we consider soil something to be managed around rather than properly managed to increase its capability to supply water, nutrients, and gases (oxygen for root growth) to a growing plant.
In the current climate change discussions, there is a large amount of attention given to the role soil management can play in terms of mitigating climate change. Sequestration of carbon into the soil and reduction of nitrous oxide emissions are often considered to be extremely significant roles for agriculture. However, these discussions often fail to consider the complete linkage in which the practices which decrease CO2 emissions are the same ones which can reverse soil degradation and ultimately lead to increases in soil water necessary to produce the food needed to meet the population demands. Likewise, the practices associated with N management responsible for reduced nitrous oxide emissions can also lead to improved crop production, higher quality of the product, and reduced water quality impacts.
Soil provides a foundation of efficient agricultural production; however, our current view does not acknowledge the critical role soil has in producing food, feed, and fiber for humankind. Erosion remains a major problem around the world and continues to degrade the soil. To combat this problem we are going to have to come to the realization that soil is a system composed of biology, chemistry, and physical structures not unlike what we have in our cities. Once we begin to understand the dynamics of this system then we can begin to understand how all of our adaptive strategies to cope with climate change will have to incorporate an understanding of the role of soil in supplying water and nutrients. There are large opportunities for soil science to feed the world and provide solutions to climate change. We have to recognize that a key component to the question can be found by looking down at our feet rather than into the stars.