Excess water in prairie soils: land management in an uncertain climate

Excess soil moisture occurs when a soil is unable to transmit water present on top of and within the soil prior to the onset of conditions harmful to soils and crops.The economic cost of excess soil moisture conditions can be very high -in 2006 the crop insurance claims in Saskatchewan alone for unseeded acres due to excess soil moisture exceeded $61 million.Three main sets of controls exist for excess soil moisture.The first controls are the hydrological ones, which control the delivery of water to the soil surface.The second controls are those that determine the partitioning of water between runoff and infiltration.The third controls are those that determine the transmission of water through the soil and sediment, including those that control the elevation of the groundwater table.Our focus in this paper is on controls that can be influenced by management and development of Beneficial Management Practices to achieve these management goals.The effects of excess soil moisture on soil chemical properties can cause both shortand long-term damage to soils.Recharge of water to the groundwater can cause an increase in the elevation of the groundwater table and the introduction of saline or sodic conditions into the rooting zone of crops.Decomposition and release of nutrients from crop residues is greatly slowed, and very high gaseous losses of nitrogen can occur through denitrification.Excess moisture can influence crop yield in two ways: 1) the inability to access the field and plant the crop at the right time (i.e., trafficability) and 2) damage to the crop due to lack of sufficient O 2 and biochemical processes triggered by the absence of O 2 (Figure 1).Trafficability issues most commonly arise in spring after snowmelt, and the inability to access the field early enough in the short growing season decreases the number of frost-free days available for plant growth and grain ripening.Seed germination, the earliest stage of plant growth, can be inhibited or even prevented by excess moisture because cell division and growth require O 2 to proceed.Where plant growth is established, excess moisture can have a significant negative impact on both root and shoot growth, eventually leading to the senescence of roots.Low O 2 concentrations limit root respiration and drastically reduce the energy available from the oxidation of glucose, with up to 95% reductions in ATP production, where ATP is the fuel for most cellular processes.Photosynthesis in waterlogging-sensitive plants also decreases rapidly under excess moisture.For many species, there is an interacting effect between the timing of excess moisture and plant growth stage, with

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