Ontario Grain Farmer April/May 2021

18 Water is a precious resource. The success of farm businesses and the health of our families depend on having a clean and abundant supply. Historically, agricultural technology has allowed us to manipulate the quantity and quality of water supplies to increase productivity. Today, this continues, with new technologies and a better understanding of natural processes. This article is the final in a series focusing on modern management of water for grain farms. Go to ontariograinfarmer.ca for more information and previous articles. LANDOWNERS CAN DIG down and find groundwater under their land, it seems to be amatter of how far one has to dig. Groundwater for some farms is a matter of keeping the level down to allow for planting while others may want to find it and use it as a water supply. Understanding the groundwater under the land may open up options for increasing yields using subsurface irrigation, controlled drainage, subsurface drip irrigation, or water supply choices in the event of a drought. Water management UNDERSTANDING GROUNDWATER John Warbick and Ian McDonald (OMAFRA), Nadia Marenco (MECP) Knowing why part of the field is wet or mushy at times, whether it is just a local wet spot or deep groundwater coming to the surface from far away can help with drainage choices and reducing compaction. Knowing how and where groundwater moves over time allows for predicting where excess nutrients or surface spills will migrate. The quality of groundwater varies in the subsurface and is influenced not only by surface activities but by the materials it migrates through as it picks up and dissolves minerals. In general, the longer groundwater stays in the subsurface and the further it travels, the more minerals it will pick up. This article provides an understanding of how groundwater works. Groundwater does not move the same in all locations, but varies with changes in Ontario’s soils, landforms, and bedrock. Ground water is a significant part of the water cycle. Previous articles in this Water Management series explained the basic water cycle. This article will detail how subsurface variability impacts groundwater. MOVEMENT Groundwater will move from areas of high elevation to areas of low elevation. The high areas are called recharge areas where precipitation water moves down to the water table and flows toward lower elevation areas. In discharge areas, groundwater is moving up and discharging at land surface or water surface. On a large scale, in excess of several kilometers, the groundwater may recharge in one area, flow down several 10s to 100s of metres in the soil and/or bedrock, move under small streams and rivers and discharge a significant distance away (Figure 1). The travel time for the water to discharge may be measured in thousands of years. In Figure 1, the regional system of groundwater flow is indicated by the red arrows. On a smaller scale, there may be groundwater flow which recharges in one Agronomy Water Table Level Silty Sand Clay Perched Water Table Wet Spot Bedrock Local System Local System Local System Intermediate System Regional System Local Recharge Local Recharge Local and Intermediate Recharge Regional Recharge Local and Regional Discharge Local and Intermediate Discharge Local Discharge Local Discharge FIGURE 1 (ABOVE): WATER CYCLE. ILLUSTRATION COURTESY OF OMAFRA. FIGURE 2 (BELOW) FIELD WET SPOT CAUSED BY PERCHED WATER TABLE. ILLUSTRATION COURTESY OF OMAFRA.