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4: Plants and Water

Finley, S. CABI PDF

4

Plants and Water

Water availability is a principal limiting factor to plant development and crop yield. In laboratory studies, the total dry matter production of crop plants has been shown to have a linear relationship to water uptake: the more water used, the more yield produced, up to the point where the full plant water requirement is met.1

Water plays several roles in plant development and crop production:

1. Water is the principal transport mechanism for moving essential nutrients, minerals and dissolved carbohydrates through plant tissues. Water moves from regions of low to high potential, pulling it from the soil into roots, upward through plant tissues, and out through the leaf surface into the atmosphere in a continuous sequence driven by transpiration. As it moves through the plant, water delivers essential elements from roots to shoots and leaves where they are used in plant metabolic processes.

2. Water is a critical reactant in chemical reactions occurring in plant cells.

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6: Soil-focused Strategies: Reducing Water Loss

Finley, S. CABI PDF

6

Soil-focused Strategies:

Reducing Water Loss

Chapter 2 introduced the concepts of productive and unproductive water uses within the overall farm water budget. Recall that the only fully productive use of water is crop transpiration (T), which is supplied by readily available soil water stored within the root zone. Typically, the percentage of rainfall that ultimately translates into transpiration is very low, in most cases between 15% and 30%.1 Unproductive water uses, including e­ vaporation, runoff, weed growth and deep percolation result in the loss of the remaining portion of the water budget. Loss percentages vary widely by context – in extreme cases, the combined forces of evaporation, runoff and deep percolation can consume more than 90% of the rainwater falling on the field.2

In order to improve rainwater productivity, farm management practices must seek to shift the way that water inputs from rain are partitioned among these competing uses. The goal is to promote infiltration and reduce water losses as much as possible, leaving more water available for use in crop transpiration.

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3: Soil and Water

Finley, S. CABI PDF

3

Soil and Water

More than anything else, the key to enhancing resilience and promoting water availability for crop growth lies in the proper care of farm soils. In fertile regions, the native soil underlying forests, brush or grasslands tends to be naturally ‘healthy’, that is, rich in nutrients with good structure and organic matter content. When land is cleared for farming, soil can quickly lose its ‘healthy’ qualities, especially if farming practices employed do not encourage its regeneration. Without proper management, agricultural soils can become completely depleted in as little as a few decades or even a few years after clearing, depending on the nature of the land and its use.1

Some negative effects that agriculture can have on the soil include:

nutrient mining (continual removal of nutrients without renewal); breakdown of organic matter; loss of water holding capacity; compaction; erosion; surface sealing (crusting); and deterioration of natural habitat for soil organisms (microorganisms, insects, and worms).

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1. The Unique Characteristics of Water and Water Rights in Texas

Porter, Charles R. Texas A&M University Press ePub

THE UNIQUE CHARACTERISTICS OF WATER AND WATER RIGHTS IN TEXAS

Determining a water right in Texas depends on which of three geological containers holds the water.1 The first container is surface water, or water that flows on the surface of the ground in a watercourse.2 The State of Texas owns the water in a watercourse. The assessment of what makes up a watercourse can be complicated, so the safest way to look at ownership of surface water is to consider all water flowing in any stream or area with bed and banks to be surface water. Surface water is not yours to own but, except in unique situations, is owned by the State of Texas. Knowing this may save you many dollars in fines and hours of angst. If you have a question about surface water ownership on real property you own or are considering purchasing, ask the Texas Commission on Environmental Quality (TCEQ) for a determination.

The second geological container is known as diffused surface water, or rainwater that runs off your roof or over the surface of your land without flowing in a stream or channel. The water in this container is owned by the landowner.

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2: Goals of Agricultural Water Management

Finley, S. CABI PDF

2

Goals of Agricultural Water

Management

Water is a vital component of every agricultural project. In addition to supporting plant growth, water is critical to maintaining soil health and promoting the overall ecological well-being of the land, which are essential in ensuring the long-term viability of the farm. In this book, the term soil and water management practices is used to designate the range of farming practices that influence the way in which water flows through the farm environment and is transformed into crop yields. This category includes methods of water application, but also cropping systems, soil management practices, and land use patterns. The purpose of this publication is to define and explain sound practices for managing water in the cultivation of field crops. While the management of soil and water resources is equally important in other agricultural categories such as livestock rearing, aquaculture and forestry, these remain outside of the scope of this book.

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