Maintaining optimal crop health is essential for improving lettuce productivity and quality. Having the right balance of plant nutrients available during the growing season is critical for their defense against plant pathogens and overall plant health. When lettuce crops are not receiving proper nutrition, they are more susceptible to a variety of abiotic and biotic stresses.
The link between crop nutrition and plant health has been studied for several years. For example, calcium is an essential component in maintaining the cell wall structure of a plant. When poor calcium nutrition occurs, the crop is more susceptible to fungi that will enter the xylem, dissolve cell walls, and cause the plant to wilt.
Dr. Rob Mikkelsen, Yara Director of Agronomic Services, summarized the mechanisms where proper fertilization can affect disease control into these main categories:
For example, crop nutrition and in particular the use of specific nitrogen fertilizer forms, can impact two resistance mechanisms that reduce the incidence of Fusarium in vegetable crops:
Nitrate nutrition (Fig. B) promotes healthier plants by reducing Fusarium disease severity compared with ammonium. Ref: Duffy and Défago - Tomatoes.
During this growing season, the local team at Yara is further exploring the additional benefits of proper crop nutrition for lettuce and the incidence of important plant health issues we are experiencing. Studies show that certain fertilizer choices encourage soil pathogen proliferation (Fusarium, Pythium, Phytophthora, Rhizoctonia) and these disease organisms may exacerbate the challenging INSV (Impatiens Necrotic Spot Virus) condition affecting lettuce in our region.
While proper fertilization does not eliminate the risk of diseases, the use of a balanced crop nutrition program for lettuce will assist in achieving productive crops despite adverse conditions. Some key components of the comprehensive crop nutritional program for lettuce include:
Nitrate is the preferred form of nitrogen fertilizer for lettuce. Studies show that susceptibility to several pathogens is much greater in the presence of ammonium nitrogen compared to nitrate nitrogen. Also, many soil pathogens are favored by acidic soil conditions and all ammonium-based nitrogen fertilizers create sites of acidity which increase the risk of several pathogen infections. YaraLiva Calcium Nitrate does not induce a residual acid reaction in the rhizosphere and thus can help suppress disease development. Calcium is essential in formatting disease-resistant cell membranes and stable cell walls. It also inhibits lettuce disorders such as tip burn. When calcium is deficient, the membrane can leak sugars and amino acids, which can stimulate the infection by pathogens.
Calcium nitrate strengthens the root cells against fungal attacks compared to other nitrogen fertilizers.
YaraTera® NITRAKAL™ is a calcium and potassium nitrate fertilizer. Plants that are deficient in potassium have impaired protein synthesis and therefore accumulate simple N compounds (amides), which are used by invading plant pathogens. Potassium can also prevent disease attacks by promoting the development of thicker outer walls in epidermal cells. Potassium adds caliper and thickness to lettuce leaves.
A balanced crop nutrition program should include both foliar and fertigated applications. An orthophosphate product like YaraVita® MAGPHOS™ (0-29-5, 4Mg) supplies foliar phosphorus to the crop for all energy reactions within the plant. Added magnesium and potassium help in photosynthesis and metabolism.
A deficiency of any nutrient, including micronutrients, will create plant stress and potential plant health problems. Foliar supply of micronutrients have shown to improve plant health while also keeping photosynthesis, carbohydrate production and plant growth at a high level.
For more information about Yara products, contact your local Yara representative