Posts Tagged ‘flooding’

Observations After the Hurricane

Friday, September 2nd, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Hurricane Irene caused less damage than expected in the region. However, there were still significant impacts on crops in Delaware. The most obvious is lodging in field corn. On the vegetable side, lodging in sweet corn varied considerably from field to field, with many escaping damage.

High winds had the potential to batter many vegetables. The largest acreage currently in the field is lima beans and looking at many fields, they weathered the storm well with minimal pod drop and foliage damage. Cucurbit fields (watermelons, cucumbers, squash, pumpkins) were much more variable with significant foliage damage in many fields. Tomatoes, peppers, and eggplants also suffered considerable damage.

Peach and apple growers had considerable fruit drop and bruising of fruits due to wind and branch contact that will reduce marketable volumes.

Rainfall totals ranged from 6 to 14 inches depending on the site but flooding was much more limited than expected. However, wet fields have led to disease issues and quality problems in snap beans, tomatoes, pickles, and other crops with increases diseases such as white mold and Phytophthora. In pickles, excess soil makes washing much more difficult and has increased fruit rots. Excess water has caused severe cracking in tomatoes and cantaloupes with much of the late summer crop ruined.

The storm has affected later watermelons to a great degree. In 2010, because of the dry year, farmers were able to keep vines healthy and continue cropping past Labor Day in many fields. Later planted fields yielded well. This year, because of the extra heat stress in July and early August followed by Irene and the current cold night temperatures, vine health has declined greatly in many fields and growth has slowed, limiting late yields. Excess water has increased water-soaking in some varieties. Later plantings that were wind damaged by Irene have open canopies causing bleaching in some fields. Volumes are down, quality has suffered, and some buyers have left the region.

While it could have been worse, Irene has cost vegetable and fruit growers significant economic losses in the region.

Flooding and Vegetables

Friday, August 26th, 2011

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

There is still considerable acreage of watermelons, sweet corn, pumpkins, beans, cabbage, potatoes, and other fresh market vegetable crops in the field on Delmarva. On the processing side, the majority of lima beans have yet to be harvested and there are significant acres of pickles, snap beans, and other processing crops in the field. Many of these crops will be at risk in the coming days due to hurricane Irene.

A late summer hurricane or tropical storm with both wind damage and excess rain can cause major issues in vegetable crops, most notably:

● Damage due to flooded soils in all vegetable crops

● Increased disease incidence in all vegetable crops

● Lodging damage in crops like sweet corn

Other articles will address diseases in with excess rainfall. I will focus on flooding effects on the physiology of vegetable plants.

Flooded and Waterlogged Soils
In flooded soils, the oxygen concentration drops to near zero within 24 hours because water replaces most of air in the soil pore space. Oxygen diffuses much more slowly in water filled pores than in open pores. Roots need oxygen to respire and have normal cell activity. When any remaining oxygen is used up by the roots in flooded or waterlogged soils, they will cease to function normally. Therefore, mineral nutrient uptake and water uptake are reduced or stopped in flooded conditions (plants will often wilt in flooded conditions because roots have shut down). There is also a buildup of ethylene in flooded soils, the plant hormone that in excess amounts can cause leaf drop and premature senescence.

In general, if flooding or waterlogging lasts for less than 48 hours, most vegetable crops can recover. Longer periods will lead to high amounts of root death and lower chances of recovery.

While there has not been much research on flooding effects on vegetables, the following are some physiological effects that have been documented:

● Oxygen starvation in root crops such as potatoes will lead to cell death in tubers and storage roots. This will appear as dark or discolored areas in the tubers or roots. In carrots and other crops where the tap root is harvested, the tap root will often die leading to the formation of unmarketable fibrous roots.

● Lack of root function and movement of water and calcium in the plant will lead to calcium related disorders in plants; most notably you will have a higher incidence of blossom end rot in tomatoes, peppers, watermelons, and several other susceptible crops.

● Leaching and denitrification losses of nitrogen and limited nitrogen uptake in flooded soils will lead to nitrogen deficiencies across most vegetable crops.

● In bean crops, flooding or waterlogging has shown to decrease flower production and increase flower and young fruit abscission or abortion.

● Ethylene buildup in saturated soil conditions can cause leaf drop, flower drop, fruit drop, or early plant decline in many vegetable crops.

Recovering from Flooding or Waterlogging
The most important thing that you can do to aid in vegetable crop recovery after floods or waterlogging is to open up the soil by cultivating (in crops that still small enough to be cultivated) as soon as you can get back into the field. This allows for oxygen to enter the soil more rapidly. Nutritionally, sidedress with 50 lbs of N where possible.

In fields that are still wet, consider foliar applications of nutrients. According to Steve Rieners at Cornell “Use a low salt liquid fertilizer to supply 4 to 5 lb nitrogen, 1 lb phosphate (P2O5) and 1 lb potash (K2O) per acre. Since nitrogen is the key nutrient to supply, spraying with urea ammonium nitrate (28 % N solution) alone can be helpful. These can be sprayed by aerial or ground application. Use 5 to 20 gallons of water per acre. The higher gallons per acre generally provide better coverage”. As with all foliar applications, keep total salt concentrations to less than 3% solutions to avoid foliage burn.

Salt Water Inumdation, Fresh Water Flooding

Friday, May 16th, 2008

Gordon Johnson, Extension Ag Agent, Kent Co.; gcjohn@udel.edu

Salt Water Inundation
Significant acreage across the state has been damaged by flooding, both with fresh rain water, and with salt water along the coast. In fields along the marsh next to the Delaware Bay, significant acreage was inundated with salt water from the tidal surge over the weekend. The tidal surge also brought large amounts of debris into these fields.

Salt water inundation occurred where fields were flooded with sea water, brackish water, or tidal surge water from the Delaware Bay. Salt contaminated soils will have several effects on crops. The first is osmotic where high salt levels in the soil solution will draw water out of germinating seedlings and the roots of plants, causing desiccation. In less severe cases, elevated salt levels will make it more difficult for plants to take up water, thus increasing water stress and reducing growth. The second concern is the toxic effect of salt water constituents. Excess sodium is toxic to crop plants. In addition, chloride from salt water can be toxic to many crops.

Soils that have had salt water leach into them will have high osmotic conditions (high dissolved solutes) and high levels of sodium. Levels of overall salts, sodium, and chloride will be reduced with leaching from rainfall, but this may take a considerable amount of time, depending on the amount of rainfall, soil type, water table, and the presence or absence of salt water intrusion in the ground water. On a sandy loam soil, salt levels may be reduced to tolerable levels within a year’s period of time. On heavier soils and soils with high water tables, it may take several years for salt levels to drop to acceptable levels. In areas where salt water ponded for long periods of time, also expect effects to last for several years. Other problems include salt water mixing with ground water contaminating shallow wells and tidal overwash into irrigation ponds, contaminating irrigation water sources.

Field crops vary in their sensitivity to high salt and high sodium levels. Soybeans are very sensitive and will not tolerate much salinity. Soybeans will not survive in any fields flooded with tidal surge waters if planted this year. Corn has more tolerance (rated as moderate salt tolerance), but again will likely not grow this year in salt water inundated soils. Sorghum and small grains have higher salt tolerance. These will be future options as salt levels drop (if they fit into your crop rotation). A number of millets also have salt tolerance.

A quick test for soluble salts is the electrical conductivity (EC) of the soil: the higher the conductivity, the higher the salts. Call your county extension office if you want to have your soils tested for EC. For sodium levels, a laboratory soil test will be needed. The Kent County extension office has an electrical conductivity meter equipped with soil probe sensors for direct soil EC measurements if you want to confirm soluble salt levels or monitor salt levels directly in fields during the year.

To reclaim a waterlogged, salt-affected soil, the water tables must be lowered, excess salts must be leached out, and where sodium is very high, it should be replaced with a more desirable cation such as calcium. The following are some strategies to manage salt affected soils:

● Moldboard plowing can help to dilute salts by mixing with the soil. Continued tillage can help keep salt that evaporates at the surface mixed with the soil.

● Irrigation, where available, will help to move salts out of the surface soil so that crops may be established. This requires significant amounts of water being applied over a long period of time so good drainage will be necessary.

● Plant salt tolerant crops once enough leaching from rainfall or irrigation has occurred. Sorghum species, including grain sorghum, sudangrass, sweet sorghum, and sorghum/sudangrass hybrids, have some salt tolerance. Many millets also are salt tolerant with Japanese millet being a good choice for salt contaminated soils. Small grains have relatively high salt tolerance. There are several perennial species such as coastal panic grass, tall fescue, and bermudagrass that have good salt tolerance. Salt tolerant alfalfa varieties are also commercially available.

● Add low salt containing organic materials to the soil such as leaf compost or yard waste compost (do not use manure, sewage sludge, or mushroom soil based compost).

Sometimes gypsum is recommended to remediate salt affected soils. Application of gypsum may or may not be beneficial. Gypsum (calcium sulfate) is a salt itself, and may actually increase the salt content in the short term. Application of gypsum to high sodium soils will provide calcium to displace the sodium. However, you still need rainfall or irrigation to leach the displaced sodium down and internal drainage to allow downward movement out of the root zone. If either of these conditions is lacking, then gypsum application alone will not help.

Fresh Water Flooding
Other areas throughout the state were flooded for a period of time with fresh water from recent heavy rains and there have been a number of questions on the effect of fresh water flooding on corn.

The extent to which flooding injures corn is determined by several factors including plant stage of development when flooding occurs, the duration of flooding, and air/soil temperatures. Prior to the 6-leaf stage (when the growing point is near or at the soil surface), corn can survive only 2-4 days of flooded conditions. Once corn has reached the silking stage shallow depths of flooding will not cause any noticeable amounts of damage. If temperatures are warm during flooding (greater than 77° F) plants may not survive 24 hours. Cooler temperatures prolong survival. Iowa studies found that flooding when corn is about 6 inches in height for 72, 48, and 24 hours reduced corn yields by 32, 22, and 18%, respectively, at a low N fertilizer level (50 lb N/acre). At a high level of N (350 lb N/acre) these yield reductions ranged from 19 to 14% in one year to less than 5% the following year.

Research indicates that the oxygen concentration approaches zero after 24-hours in a flooded soil. Without oxygen, the plant cannot perform critical life sustaining functions – nutrient and water uptake is impaired, root growth is inhibited, etc. Even if flooding doesn’t kill plants outright it may have a long term negative impact on crop performance. If excess moisture in the early vegetative stages retards root development, plants may be subject to greater injury during a dry summer because root systems are not sufficiently developed to access available subsoil water.

If flooding in corn is less than 48 hours, crop injury should be limited. To confirm plant survival, check the color of the growing point (it should be white and cream colored, while a darkening or softening usually precedes plant death) and look for new leaf growth 3 to 5 days after water drains from the field.

Cold, wet weather conditions also favor development of seed rots and seedling blights. Seed treatments are usually effective but can provide protection only so long; if seedling development is slowed or delayed 2-3 weeks, soil-borne pathogens have a much greater opportunity to cause damage. Other disease problems which may become greater risks due to flooding and cool temperatures are corn smut and crazy top. The fungus that causes crazy top depends on saturated soil conditions to infect corn seedlings. There is limited hybrid resistance to these diseases and predicting damage is difficult because disease symptoms do not appear until later in the growing season.

Information on salt water flooding by Gordon Johnson, Extension Agriculture Agent, UD. Information on corn flooding from Peter R. Thomison, Extension Agronomist, the Ohio State University