Michigan Right to Farm Act Irrigation Generally Accepted Agricultural Management Practices for 2013.
No major changes are proposed for the 2014 irrigation GAAMP.
The following were removed from the GAAMPs in 2012 and are provided there for educational purposes. This information is also presented in other parts of the web site. Planning and Preparation Irrigation is used to provide moisture for plants when natural rainfall, coupled with the soil’s capacity to store available moisture, is insufficient. Plants obtain needed moisture from water stored in the soil. The need for irrigation depends upon how much water the soil can store and how frequently rainfall occurs. In Michigan, the annual rainfall exceeds annual water use by plants, but the temporal distribution of precipitation is not sufficient to keep up with plant needs unless the soil can store several inches of available moisture. Where soils have high moisture holding capacity and crops with the capability of developing roots several feet in depth are grown, irrigation may not be necessary. Irrigation is beneficial and necessary for crops grown on sandy soils that have limited ability to store moisture. Planning for irrigation should include consideration of: · The soil/substrate and its moisture holding capacity · Crops to be grown and their rooting depths · Susceptibility of the crop to moisture stress · Available water supply for irrigation and other nearby users · The overall economics of investing in irrigation Water Supply: Planning for irrigation includes not only determining whether irrigation would be beneficial based upon soil, plant, and economic characteristics, but also the assessment of whether an adequate water supply capable of providing the quantity of water needed in the driest years exists. In most areas of the state where irrigation is practiced, the water supply is more than adequate. Groundwater supplies are sufficiently abundant for irrigation and other uses in most of Michigan, even in exceptionally dry years. However, there are some areas where groundwater may not be sufficient for all uses, even in years of average precipitation. As a general rule, irrigation systems in Michigan should be capable of keeping up with a plant water use rate of about 0.25 inches per day over the entire irrigated area. The flow rate required will depend upon the percentage of the total time the irrigation system can be expected to operate considering the necessary downtime for maintenance and making new irrigation sets. For example, center pivot irrigation systems can be expected to operate nearly 24 hours per day, but other systems such as ‘traveling big guns’ require downtime for making new sets. System capacity planning must take into account that less than 100 percent of the water applied is actually stored in the root zone. Procedures for planning irrigation water needs are outlined in detail in MWPSâ€‘30 (1999). Water supplies for sprinkler irrigation systems that wet the entire surface area must be capable of providing at least five gallons per minute for each irrigated acre. Requirements for drip (trickle) irrigation used for trees or other crops, and irrigation practices where the plant foliage and the wetting process does not cover the entire area, may be less. Water for irrigation may come directly from groundwater or surface water sources, or in some cases of turf and landscape or nursery production, from municipal supplies. Procedures for evaluating surface water sources to determine adequacy for irrigation are provided in MWPS-30 (1999). Some surface water, such as streams, lakes, and wetlands, may be sensitive to large withdrawals of groundwater for irrigation. Nearly all groundwater naturally flows out to surface water. Groundwater removed from an aquifer for irrigation may reduce this flow to surface water. Plants and animals in surface water depend upon groundwater, which help to maintain stable temperature, chemistry, and flow. Surface waters that may be most affected by nearby irrigation from groundwater are smaller lakes, wetlands, and headwater streams. The irrigation season is typically a time period when these smaller surface-water bodies are most reliant upon groundwater. Aquifer Monitoring: Irrigation with groundwater also has the potential to lower water levels in nearby wells. It is difficult and expensive to determine a potential affect prior to installing a new irrigation well. Well drillers, nearby irrigators, extension agents, universities, , MDARD, MDEQ, or USGS, may have information about potential effects of irrigation on nearby wells. In areas where there is a known potential to lower water levels in nearby wells, an irrigator may wish to install one or more monitoring wells. Such wells should be drilled to the same aquifer as potentially affected wells. They should be located between the irrigation well and potentially affected wells and as far away as possible from the irrigation well. All well work should be performed by a licensed, Michigan, water well drilling contractor. Irrigation well design should include drilling and test pumping of a test well prior to installing the irrigation well. By carefully monitoring the water level in a test well during an appropriately long period of pumping, the driller will be able to predict the performance of the irrigation well. Water levels in an irrigation well should be monitored, both to determine the effect of pumping on the aquifer and to determine if the well is approaching a need for maintenance. The irrigation well should be set up with monitoring equipment so that it is easy to monitor the water level in the well. An air line and specially calibrated gauge may be installed on the well for this purpose. Measurements of water level should be made prior to the irrigation season, approximately midway through the irrigation season, and after the irrigation season. For monitoring the long-term conditions in the aquifer, these measurement dates should be on about the same date every year. Water level measurements prior to and after the irrigation season should be made when the pump has been off for several days. Water level measurements during the irrigation season should be made while the pump has been operating for some time (for instance, just prior to shut-off), and when the pump has been off for some time (for instance, just prior to irrigating). Long-term records should be kept on these measurements to provide data on any change of aquifer level or lack thereof. Dynamic pumping levels can reveal a change in well efficiency that may indicate a need for service. If both pumping and non-pumping levels are measured annually, these records are useful for system maintenance. They can be used to detect any change in well efficiency or pump performance. If the drawdown, the difference between non-pumping and pumping level, increases, it is an indication that the well screen or the formation around the well is becoming plugged and may need maintenance. If the drawdown decreases, it may be an indication that the pump is not pumping as much and may be becoming worn, or there is a severe restriction to flow somewhere. If an irrigator is using monitoring wells to determine impact on the aquifer, they should be measured more frequently. During the irrigation season, water levels should be measured as frequently as possible, but not less than once a week. During the remainder of the year, water levels should be measured not less than once a month. Preferably, all measurements should be taken at about the same time of day. In all monitoring, either of the irrigation well or monitoring wells, care must be taken to avoid aquifer contamination. “To protect the aquifer from contamination, Part 127, PA 368 of 1978, as amended, requires all wells be properly plugged upon abandonment of the well. Technical assistance on the proper closure of wells may be obtained from the soil conservation district office.” Irrigation Equipment: There is a variety of irrigation equipment available. Most irrigation systems in Michigan are overhead sprinkler systems. Where crop foliage does not develop to provide complete ground cover, drip or micro-sprinkler irrigation systems may provide greater water use efficiency. The application characteristics of the irrigation system should be matched to the intake characteristics of the soil. Information on soil intake rates is available from NRCS soil survey data and should be consulted in choosing the sprinkler package or specific sprinkler system to be utilized. Water that does not infiltrate during application is not beneficial. Water that runs off one spot may move to another, causing over infiltration resulting in nutrient and pesticide leaching and inefficient water use. It may also result in water leaving the field and entering a waterway resulting in potential water quality impacts. The "Planning and Preparation", "Water Supply", and "Irrigation Equipment" sections above are referenced in GAAMPs. There were removed from the GAAMPs in 2012 and are provided there for educational purposes.