Irrigation Managment Guide to Best Practices Spud Smart Winter 2011

Irrigation Management:
A Guide to Best Practices

Best management practices mean striking a balance between ideal crop conditions and environmental protection.

POTATOES ARE a water-sensitive crop, and are often considered to be a water-intensive crop. This is partially true but needs to be taken in context. Although potato plants need a fair amount of water during the growing season to produce at their optimum levels, their prime need is not only total volume of water, but also the frequency at which water is available to the plants once the soil dries out.

Potatoes have a relatively shallow root system. The crop is most often planted on sandier soils with low capacities for water retention, and responds negatively to even short periods of inadequate water availability in the root zone, which means a potato crop should receive a regular replenishment of soil moisture throughout the growing season. Although total volume of water is important, the frequency of watering is of similar importance.

All of these factors when taken into consideration are, in most cases, the reason why a large majority of potato growers choose to invest in an irrigation system for successful potato production. In most areas where potatoes are cultivated in Canada, rain, in and of itself, cannot at all times fulfill the water needs of a potato crop; although in some regions it does not make economic sense to irrigate since the return on investment over time is not good enough to warrant the installation of an irrigation system.

Having the means available to irrigate a potato crop (be that a pivot system, solid sprinkler set or other equipment) is the very beginning of the road on the journey toward successful irrigation and a favourable crop outcome at harvest time. Management of the irrigation system is what it’s all about, as most potato growers know from experience. Furthermore, management, as such, is one thing—best management is the real challenge.

Strike a Balance

Best management practices for potato irrigation are the eventual outcomes of a grower’s common sense, attention to detail and proven agronomic facts (as determined by researchers and other crop experts). In order to “best manage” an irrigation system during the growing season, a potato grower needs to know the answers to the following questions: When? Where? How much?

In a nutshell, it comes down to knowing what your crop requirements are for water, and fulfilling those needs at the right time, in the right place, and with the right amount to grow and produce high-quality yields.

Irrigators who have clear answers to these questions have a good chance of making a success of their irrigated crops. Also—and at the core of BMPs—growers must think and act beyond producing a great crop: they should also keep in mind the effect their practices have on the environment. This is the reason potato irrigation specialists Andre Pereira and Clinton Shock in their research paper Development of Irrigation Best Management Practices for Potato from a Research Perspective in the United States define BMPs as “the proper management of irrigation applications to meet the water requirements of the crop, without wasting water, soil or nutrient resources.” BMPs for potato irrigation are designed to strike a balance between ideal crop conditions and environmental protection.

The following information focuses on a few of the most crucial principles potato growers should bear in mind when striving to irrigate their crops according to the requirements of BMPs.

Know Your Source

It is of great importance that a grower is familiar with the water source used for irrigation. The main principle is to know your source. Growers must be able to answer the following questions:

• How much water, in total, is available for irrigation use without causing harm to the environment while ensuring enough water is available to see the crop through a worst-case scenario of prolonged drought?

• How sustainable is the source? Will it last for the duration of the season?

• What is the quality of the water (based on a lab analysis completed before the start of irrigation)?

Understand Your System

A grower needs to be familiar with the particular irrigation system in use. An important principle is to understand your system. Continuous maintenance to irrigation systems is necessary to ensure the most efficient use of the water that is being applied. Growers should consider the following questions:

• How much water can the system deliver during a particular period of time?

• How much energy does it use during a typical irrigation session?

• Has the system been professionally serviced before and after the season?

• What parts of the equipment might typically cause problems during the season?

• Are spare parts readily available or in stock at the farm and/or supplier for the most crucial elements of the system that may need replacement or repair during the season?

• Is the main operator of the system familiar with the mechanics and capabilities of the system?

• Is there a backup plan in place in case the system becomes inoperative during a crucial period of the growing season?

• Are efficient winterization practices in place?

Understand Your Soil

Growers need to be familiar with the type of soil in their fields when irrigating. The core principle is to analyze and understand your soil. It is near impossible for growers to do accurate irrigation scheduling if they are not totally familiar with the nature of the soil profile; this is at the heart of an irrigation schedule. The more detailed knowledge a grower has of the soil in the field, the better. Consider the following:

• What is the water-holding capacity of the soil?

• What is the permeability of the soil (a measure of the ability of air and water to move through it)?

• What is the nature of the soil structure and texture?

• How long does it take the soil of a particular field to dry out after an irrigation cycle when no rain falls during a certain period of time? How long for the soil to dry out if a particular amount of rain is received?

Know Your Field

Growers need to be familiar with the fields to be irrigated to compensate for potential problems that might arise due to the individuality of those fields. The principle at stake is to know your field. This knowledge can only be determined by applying the dirty boots concept—being there in the field, in person. Answers to the following questions should be considered:

• Are there hollow areas where water can potentially accumulate and cause problems when irrigating?

• Are certain areas in the field prone to over- or under-watering due to soil structure and texture?

• Is there a danger that overwatering might cause significant erosion in certain parts of the field?

• Is the field structure completely suitable for the specific piece of equipment used for irrigation or will another field be better, or might a different system be more suitable?

Potato Varieties and Water Requirements

It is a fact that different potato varieties have different water requirements. The principle is for growers to know how much water does the irrigated variety typically need. This need must be considered with respect to the growth stage of the variety at specific times during the growing season.

Irrigation Scheduling

A grower has to define a basic irrigation schedule at the start of the season and be ready to amend that schedule based on practical realities, which will only become apparent as the season progresses in terms of the crop’s water requirements at specific time periods. Growing a crop of potatoes typically requires 400–500 millimetres (16–20 inches) of water depending on prevailing weather and variety. This includes the available soil moisture in the spring, which varies depending on soil type. The crucial principle related to an effective schedule is to have a basic scheduling plan ready and adapt as you go.

• Is the irrigation schedule based on practical experience as well as advice provided by an agronomy specialist?

• Is the schedule based on facts obtained from scientific data related to the nature of the soil, the variety type, prevailing weather, capacity of the water source, the technical abilities of the equipment, and so forth?

• Are sufficient and appropriate technological tools in place to assist with decision making; for example, soil moisture blocks using electrical resistance, time-domain reflectrometry equipment, or electrical capacitance-based products?

• Have these tools been calibrated for the soil type and variety under irrigation?

If no tools are used, is the grower familiar and comfortable with applying the “feel and appearance” method of measuring soil moisture?

Use, Don’t Abuse

Water availability and water quality issues have become predominant public environmental concerns during the last decade. Groundwater in many areas has become contaminated with nitrate and pesticide residues due to leaching caused by irrigation—especially over-irrigation. Growers irrigating their fields should take note of contamination issues and ensure that their management practices aim to minimize environmental risks. The core principle is to use, but don’t abuse.

When planning for the coming growing season, growers should consider taking another look at their current irrigation practices; with a little tweaking, current practices may be altered to fit better with the principles of acceptable BMPs.

Lukie Pieterse