Spoon Feeding Crops

 

Crops are starting to grow faster with warmer temperatures after a cool wet spring with entering rapid nutrient uptake and plant growth. Most plant nutrients are absorbed through the roots. Some nutrients get locked up in the soil making them unavailable to the plant. There are many factors that contribute to nutrient soil immobilization. If the fertilizer solution pH is too high or too low, nutrient deficient, or excessive; some nutrients might not be absorbed. Low soil organic matter, reduced microbial activity, damaged root systems, excessive water or a lack of water can all lead to lower rates of plant nutrient uptake and absorption. Many farmers regularly use some foliar feeding with herbicides or fungicides to enhance crop growth and yield.

The leaves, and sometimes even the stems, of many plants are equipped with tiny, pore-like structures called stomata. Stomata open and close at certain times of the day. Stomata have two major functions. Stomata allow oxygen and water vapor to leave the plant to cools the plant. This process called transpiration allows for water and nutrients to flow from the roots to the leaf cells. Stomata also absorb carbon dioxide for photosynthesis. Stomata can also be a plant opening for absorbing liquid plant nutrients, however timing is critical.

Stomata opening and closing is affected by environmental conditions. Stomata are generally open during periods of high light intensity which allows carbon dioxide in for photosynthesis. Stomata also open during times of high humidity, when water is plentiful and plants don't need to conserve water. However, stomata remain closed when conditions are exceedingly hot (above 80°F) or very dry, when a plant will keep its stomata closed to conserve water. For foliar feeding in hot summer months; spray in the morning or early evening and in sunlight when the weather is still relatively cool. Here are some foliar feeding tips.

First, the ideal nutrient spray pH is right around 7.0 or neutral. In the spray tank, agitation may be necessary to keep nutrients from precipitating to the bottom. Avoid foliar feeding when temperatures are above 80°F. In the summer it's best to spray either in the morning or early evening, when temperatures are lower (72°F is best). Spray between 7AM and 10AM or after 5PM for best results. Avoid foliar feeding during the hottest part of the day when the stomata are closed. Foliar feed when weather conditions are more humid for better results.

When mixing foliar nutrients, remember that nutrient solution mixes should be more diluted than you would for root feeding. Excess salts (positive and negative ions) in fertilizer can harm plants. Finer and smaller nutrients enter stomata and leaf cuticle pores easier than large forms. For most micronutrients, the sulfate form tends to be water soluble and the easiest to get into solution. Use sprayer tips that create fine mists to get an even leaf spray pattern.

Wetting agents, surfactants, and fulvic acid improve performance. High surface tension in water causes it to bead up and reduces water absorption when sprayed. A wetting agent or surfactant lowers water's surface tension, allowing for smaller water molecules to be absorbed or use rain water or structured water for best results. Fulvic acid aid micronutrients movement into a plant leaves, stems, and roots. Spray both the tops and bottoms of the leaf until they are completely covered, if possible. Do not apply foliar fertilizer so that droplets form on leaves. This may cause leaf burn.

Minnesota research shows that nutrients may be taken in though the leaf cuticle. Leaf cuticles contain many micro-pores (< 1 nanometer) which are lined with negative charges that are attracted to positively charged elements. Calcium, magnesium, potassium and many micronutrients (iron, zinc, copper, manganese) are all positively charged. Negatively charged anions like phosphorus and sulfur are more difficult to move into the plant because they are repelled. Movement through the cuticle is dependent upon many factors including nutrient concentration, molecular size, nutrient form, etc. If you suspect a particular nutrient deficiency, cut a leaf and dip in a foliar nutrient solution. If the nutrient is needed, the cut leaf color should improve. Generally, on a whole plant leaf, if successful; color changes and improved growth may occur within 24-48 hours after foliar application.

Foliar feeding can be effective method to supply a plant with micronutrients and as a short-term solution to many different nutrient deficiencies. However, if fields nutrient deficiencies occur on a consistent basis, foliar feeding is not the answer. A majority of plant nutrition comes from the soil. Foliar feeding is often a temporary fix instead of a permanent solution; labor intensive, and rather expensive on a large scale.