Strategies after heavy rain / floods

The recent heavy rain has had a significant impact on our land, pastures and crops ‐ while some of us just received heavy rain, others were flooded with land being covered with water for days or weeks. As it dries out there are a few rules which we should follow.

• Prevent severe soil compacting. Avoid driving trucks and heavy farm equipment over wet soils. Most soils are not dry enough for traffic or cultivation until the top 5 or 6 inches crumble, rather than slick over or pack. • Encourage the growth of cover crops such as rye or wheat. Any type of plant growth is effective in drying waterlogged soils. • Apply compost to soil that has lost topsoil and organic matter. • Take soil samples to determine new fertility levels. The fertility level of flooded soils is likely to have altered significantly. Do not guess at requirements. Now is the best time to take samples for pastures while fruit crops should be sampled at the end of summer/beginning of autumn

Many factors affect the extent of crop damage after a flood. Seasonal temperatures can be a majorfactor. During spring flooding, temperatures are colder, and plants can survive longer under water. Plants that encounter flash‐flooding along creeks where the water rises and recedes quickly are most likely to survive. They will experience less oxygen depletion than submerged plants. Other factors for survival include water movement and plant height. Standing water is more harmful than moving water. Plants with some leaves protruding from the water are more likely to live. Restoration of lucerne, irrigated pastures, perennials and hay will depend heavily on all of these factors, but it also depends on the steps you take toward recovery.

Strategies for this Year and Next Floods can affect weeds both the year they occur and in subsequent years. The biggest impact in the flood year will be the reduced competitive ability of the crop. Weeds will take advantage of stunted or failed crops and grow to maturity. In the year after a flood, any un‐germinated weed seed carried in may cause new problems, therefore mechanical and chemical methods need to be considered in both the flood year and subsequent years to manage weeds.

Water logging for prolonged periods often induces a process called de‐nitrification. This process acts under anaerobic conditions (lack of oxygen), where de‐nitrifying bacteria convert nitrate nitrogen to gaseous forms which are then lost to the atmosphere. Attempts to reverse nitrogen deficiency, (seen as yellowing crops, especially older foliage), by adding more nitrogen fertiliser to waterlogged soil may not be effective because the added nitrogen may be lost to the crop through de‐nitrification.

Tools to Help Combat the Effects of Waterlogging Nitrogen reacts with cations such as calcium and potassium in the soil solution and during heavy rainfall periods these nutrients can be easily lost due to leaching. Like nitrate, boron and sulphur also exist in the soil as anions and are particularly prone to leaching in waterlogged conditions. Boron is responsible for sap pressure and plays a huge role in flower viability, ensuring that trees achieve a good flower‐to‐fruit set ratio. Silicon is another element that is extremely useful to apply at this time because of its ability to physically strengthen plant cell walls. This means that plants strengthened with silica are more resistant to pest and disease attack while being less likely to lodge and wilt.