5.7: What Comes From the Sky- The Lifeblood of Ecosystems

We need to take a short diversion from our focus on soils and briefly discuss climate. Various characteristics of precipitation affect the potential for crop production and the losses of water, sediment and contaminants to the environment. These include the annual amount of precipitation (for example, an arid versus humid climate); the seasonal distribution and relation to the growing season (wet seasons and dry seasons; can rainfall supply the crops or is irrigation routinely needed?); and the intensity, duration and frequency of rain (regular gentle showers are better than infrequent intense storms that may cause runoff and erosion).

Precipitation patterns are hardly ever ideal, and most agricultural systems have to deal with shortages of water at some time during the growing season, which remains the most significant yield-limiting factor worldwide. Water excess can also be a big problem, especially in humid regions or monsoonal tropics. In that case the main problem is not the excess water itself but the lack of air exchange and oxygen. Many management practices focus on limiting the effects of these climatic deficiencies. Subsurface drainage and raised beds remove excess water and facilitate aeration; irrigation overcomes inadequate rainfall; aquatic crops like rice allow for grain production in poorly drained soil; and so forth. (See Chapter 17 for a discussion of irrigation and drainage.) So, climate affects how soils function and the processes occurring in soils. What is perhaps less understood is that good soil management and healthy soils are important to reducing susceptibility to climatic vagaries and making soils and crops more resilient to weather extremes. The Great Plains area of the United States learned this during the Dust Bowl era of the 1930s, when a decade of drought and unsustainable soil management practices resulted in excessive wind and water erosion, crop failures, the collapse of the agricultural industry, and massive human migrations out of the region. That devastating experience gave birth to the soil conservation movement, which has achieved much; but most soils, even in the United States, are still in need of protection from erosion, which requires good soil management practices.

Climate Risk and Resilience

The concept of risk integrates the cost of an adverse event with the chance of it occurring. With increasing frequency of weather extremes, the risk of costly or catastrophic events affecting farms and communities goes up. Their vulnerability is characterized by three aspects:

• Exposure: weather-related challenges you are likely to face
• Sensitivity: how and to what degree those events threaten your operation
• Adaptive capacity: how well you can minimize weather-related damage and take advantage of new opportunities

Generally, exposure to extreme weather events is a given, although farmers can help reduce overall greenhouse gas emissions through better cropping systems and nutrient management. Sensitivity to adverse weather events can be addressed through many of the practices we discuss in this book, as well as through other strategies, such as building soil health and thereby enhancing crop vigor while reducing runoff and crop drought stress; diversifying crop and livestock systems to spread risk from an extreme event; incorporating climate risk management into farm planning; building skills and experience with farm staff; installing physical infrastructure like irrigation or drainage; building social networks that allow you to respond better to adverse events; and managing finances and insurance to absorb setbacks.

By building an overall resilient farm operation you reduce potential damages and allow for faster recovery from weather-related disruptions. Still, after-the-fact adaptations still need to be anticipated, like growing an alternative crop when your initial crop was lost and using a weather-adaptive nitrogen management tool.

Adapted from Lengnick (2015)

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