The Agronomy of Water
Figure 1 – Crop yield and quality are strongly influenced by the agronomy of water and the quality of applied irrigation and spray water. The factors that make up a good water quality management strategy include salinity management, nutrient management, irrigation system management, and pesticide spray water quality.
Introduction
Water ties all aspects of crop production together and is the largest input on most farm operations on a per acre basis. Water quality is important to four categories of farm management: 1) salinity control, 2) nutrient management, 3) irrigation efficiency and distribution uniformity, and 4) pesticide (agricultural chemical) efficacy (Figure 1). It is essential to consider “the agronomy of water” and develop a water sampling program for an operation. Also, note the utility derived from water sample data and the periodic inspection of irrigation systems for managing this important natural resource. Remember, a water sample can help inform the management strategy of the four categories described below, often in the same analysis! Thus, a water sample often allows you to “quadruple-dip”for the price of one analysis.
Salinity Management
Soil salinity is often caused by the application of irrigation water that is high in dissolved salts, particularly sodium, chlorine, and boron. These ions can cause a loss in crop yield due to specific ion toxicities (e.g., boron toxicity) and, in the case of sodium, can drive a loss of soil structure, impairing drainage and impeding water penetration and infiltration. In a study from 2000, it was estimated that roughly half of all total arable acres in California were negatively influenced by saline soils and irrigation water to some degree and that this problem could get worse if not treated. A water sample can help quantify your risk of salt damage to your fields and crops and help you formulate a proactive reclamation plan.
Nutrient Management
All irrigation water contains dissolved ions. Most often, we think of the ions that cause salinity issues and toxicities, as described previously. However, due to recent regulation, we now have to think about the nutrient content of water applied to field to help mitigate groundwater pollution risk. A water sample can help estimate the presence of nitrates in your irrigation water and contribute to an improved understanding regarding on-field nutrient compliance.
Irrigation Efficiency and Distribution Uniformity
Ok, so you have the water, now you just have to apply it to the crop, right? Not so fast! Ions in the water can interact with each other and form solid precipitates in the drip emitters, sprinkler heads, and other types of nozzles. Once these precipitates clog your system, you may have to use more water and power to deliver the same irrigation set to your thirsty crops. The over- or under application of water, relative to crop needs, can result in reduced irrigation efficiencies. Furthermore, the clogging of lines can impact some parts of the field more than others, causing an issue with the distribution uniformity, which is the spatial variation of your water delivery. A water sample can help you understand drip system clogging risk and help formulate a plan to deal with it. Further fieldwork is required to quantify changes in distribution uniformity across a field but it can be beneficial for improving overall irrigation efficiency. A review of the irrigation schedule can help resolve irrigation inefficiencies.
Agricultural Chemical Efficacy
How good is your spray water quality?This simple question demonstrates the connection between your pesticide programs (e.g., agricultural chemical) and the most common mechanism for conveyance (e.g., water!). However, the constituents of the water can have severe impacts on the overall pest control wrought by your agricultural chemical spray (e.g., efficacy). A pesticide spray that controls a pest to a high degree per application has high efficacy. An agricultural chemical spray that doesn’t quite do the job has low efficacy. Efficacy is strongly influenced by the interaction between the active ingredient in your applied pesticide and the water it is mixed with (e.g., spray tank, chemigation, etc.). Five main physical components of water can have a negative influence on efficacy: pH, bicarbonates, hardness, total dissolved solids, and turbidity. Some pesticides are more strongly influenced by these components than others and management programs should work to improve efficacy on a case by case basis. A water sample can help you determine how your agricultural chemical sprays interact with water quality and help you put together a water conditioning and adjuvant plan to help improve the overall activity and control of your pesticide programs.
Take a Water Sample!
The importance of understanding your water supply cannot be understated, and a water sampling program will help you form a solid foundation of “water” agronomy and will produce tangible benefits for most farm operations. Ironically, as water is often the largest farm input, a water sample can be one of the cheapest inputs (e.g., $/acre) around as one water source can serve multiple acres on a given ranch. However, many folks do not pay close attention to aspects of water quality and do not have a regular water sampling program in place. Talk to your Helena representative today about starting a water sampling program and how we can partner to improve the agronomy of water on your farm operation across the four categories described above.
Suggested Reading
1) Irrigation Water Salinity and Crop Production – http://anrcatalog.ucanr.edu/pdf/8066.pdf
2) The Impact of Water Quality on Pesticide Performance - https://www.extension.purdue.edu/extmedia/ppp/ppp-86.pdf
3) Water Quality for Crop Production - https://ag.umass.edu/sites/ag.umass.edu/files/book/pdf/ghbmpwaterqualityforcropprod.pdf
- Dr. Karl Wyant, Lead Agronomist – Western Division