Heavy rains, floods and what can be done in fruit and vegetable farms to protect crops
Just over a week ago more than 10’’ of rain fell in less than 24 hours in some parts of the state. Since then we have had more rain showers pushing some rain totals to over 12’’ over the last seven days. Average annual rainfall in most parts of Arkansas is 45-50’’. That means we got upward of a ¼ of our annual rainfall in one week. Many row crop farmers are hurting due to rains hitting early planted crops (see estimates of crop loss here: https://www.uaex.edu/media-resources/news/september2016/09-08-2016-Ark-Rain-Crop-Losses.aspx).
Some of our fruit & vegetable crops on lower ground have also been affected.
Here are a few considerations fruit and vegetable growers should make as we get a string of much needed sunny days over the next week.
1. Pre-plant fertilizer?
Is that nitrogen you put out a week ago, still there? The short answer is probably: No. Nitrogen is readily leached by water from the soil and nitrogen uptake into the plant is inhibited under saturated soil conditions. Growers will want to watch their crop development and may choose to side-dress or inject nitrogen fertilizers as soon as the soil dries out. Foliar applications of nitrogen are also an option if soils stay wet for extended periods of time that inhibit the use of fertigation. In flooded soils Nitrate based fertilizers are preferred over ammonium based fertilizers. Research at the University of Florida found potassium nitrate to help alleviate stress associated with saturated soils (Liu et al, Publication #SL 206). Potassium nitrate can be applied as a foliar spray. The age of the crop in question and plans for future fertilization should dictate the rate of nitrogen fertilizer applied now. A good recovery rate of nitrogen for most crops in the next week would be 4-5 lbs. of N per acre (or 30.7-38.4 lbs. of potassium nitrate).
2. Waterlogged Soils- Transplants
Plants should recover within 3-10 days after water drains from the field. As fields dry out and equipment can be brought back into the field light cultivation around young plants may help bring air back into the soil. . If crops were lost and immediate re-planting is not possible a short-term cover crop like buckwheat which can be planted and mowed in as short as 5 weeks may be a good option to provide short-term soil cover.
3. Waterlogged Soils- Plasticulture Raised beds
If water rises up over the shoulders of the bed it will quickly soak into the planting holes causing the bed to become saturated. Once saturated the beds can take a long-time to dry out which can lead to crop loss.
If soils stayed water logged for less than 48 hours most vegetable crops will recover. Perennial fruit crops may also recover if flooded for less than 48 hours but yields will likely be affected this year and possibly even into the following year. The longer the flooding the greater the chances that roots start to shut down due to the lack of oxygen in the soil that gets pushed out by the water.
Signs of damage to look for:
- Flower, leaf, or fruit drop are all symptoms of waterlogging stress on plants.
- Root crops may show areas of cell death that appear as dark areas. If the main tap root of the carrot is killed secondary fibrous roots will form which are not marketable.
- A higher incidence of Blossom end rot might be expected to show up on some of our early tomato, pepper or melon crops. Blossom end rot is when there is a lack of calcium in the plant that results in rot like symptoms opposite the stem end. During flooding the roots shut down and stop taking up water or nutrients which can lead to these symptoms.
4. Food Safety and Crop Loss Due to Rot
At this early stage in the season we do not have large quantities of harvestable crops state-wide, however some lettuces, squash, strawberries and other crops are being harvested and are also low growing crops that may come into direct contact with flood waters. There are two major concerns when flood waters come in contact with ripe produce: rot and food safety.
The incidence of rot will vary based on the type of produce with lettuces and strawberries being more susceptible to deterioration than squash due to it’s tougher skin.
Direct contact of flood water and produce that is ready for harvest can be a major food safety concern. Flood water from streams/ rivers is more likely to contain human pathogens than surface water. Ripe produce that has come in contact with flood waters should not be harvested for sale, this is a rule implemented by the Food and Drug Administration (FDA). Immature produce should be handled appropriately when harvested in the future including washing with chlorinated water.
5. Eyes out for disease
Wet conditions favor disease out breaks. Fungicide programs should be maintained for foliar and particularly root pathogens. Phytopthera and Pythium both thrive under wet soil conditions.
Strawberry growers in many parts of the state were at their peaks of harvest or just past when the rains hit last weekend. Red berries can quickly turn soggy with just an inch of rain but if growers were doing a good job of keeping the crop picked up to when rains started, clean up should be easier. Overripe and soft berries should be removed from the plants and ideally removed from the fields. Luckily we are mostly on the down-hill slope of the strawberry crop with 2-3 (or maybe 4 if the cool weather holds) more weeks of picking. Growers should keep an eye out for flare-ups of gray mold and anthracnose. Root rots could also become a problem in fields that stayed wet for extended periods.
6. Improving Water drainage in fields
Water drainage management is of particular concern in plasticulture bed systems where water sheds from plastic beds into the row middles. Growers should consider row orientation and if cutting drainage channels at the ends of rows will help the field shed water. Using a shank or sub-soiler between beds to help break up layers of compaction particularly in row middles that experience heavy traffic may help improve water infiltration into the soil. It is always important to keep in mind deep tillage usually doesn’t result in long-term improvements to soil structure and can rapidly deplete soil organic matter which actually helps improve water infiltration. Deep rooted cover crops, like sorghum sudan, can help to break up layers of compaction over time