Applications of Phosphorous Acid in Agriculture

Phosphorous acid can effectively activate micronutrients such as calcium, iron, zinc, copper, and manganese in the soil. The resulting inorganic salts make these elements easier for plant roots to absorb, correcting nutrient deficiencies. It is important to note that there is a crucial issue of maintaining a proper ratio during the chelation of micronutrients. If this ratio is not properly controlled, precipitation or antagonism can easily occur, preventing crop absorption and potentially causing soil compaction and fertilizer ineffectiveness.Phosphorous acid is also a raw material for synthesizing some organophosphorus pesticides. As a strong dibasic acid, it cannot be used directly in agriculture. Direct spraying onto crops would cause severe corrosive damage and is extremely unsafe for operators. The main agricultural applications of phosphorous acid are the synthesis of potassium phosphite, calcium, copper, and zinc salts. Different phosphites have completely different applications and effects on crops. Trivalent phosphorus is highly effective against diseases caused by oomycetes, such as downy mildew, late blight, Phytophthora root rot, and scab. It works by inhibiting fungal cell wall synthesis and spore germination. Long-term use can stimulate crops to produce phytoalexins and lignin, enhancing their resistance to fungal and bacterial diseases.

Phosphorous acid can be used in fruit trees, vegetables, grains, and cash crops, playing an increasingly important role in disease control, growth promotion, and quality improvement. Spraying potassium phosphite 1-2 times each during the flowering and young fruit stages of Wogan tangerines can reduce the disease incidence to 5%. Spraying potassium phosphite 3 times during the grape fruit expansion stage increases grape sweetness from 15 degrees to 18 degrees Brix and improves color uniformity by 40%. Using a combination of amino acid-containing potassium phosphite and mancozeb for integrated control of grape downy mildew also reduces the impact of downy mildew on grape yield. A combination of potassium phosphite spraying and trunk spraying was used to control kiwifruit canker. Spraying began when the temperature was consistently below 15℃ and continued for 4-5 applications. This approach avoided chemical pesticide residues and effectively controlled the spread of canker, resulting in significant and environmentally friendly control. Foliar spraying of potassium phosphite during the potato seedling, tuber formation, tuber enlargement, and starch accumulation stages effectively prevented late blight and extended the potato growing season. It also significantly increased plant height, stem diameter, number of tubers per plant, and fresh root weight, resulting in yield increases of 15.37% and 21.51% per mu, respectively. Its effects were similar to those of fungicides such as mancozeb and metalaxyl; after 9 months of storage, the rot rate was only 0.50%. The combination of 4% tetraflufenicol emulsifiable concentrate and potassium phosphite aqueous solution containing amino acids achieved a control effect of 89.9% against powdery mildew in melons. Moreover, this combination is safe for melon growth and will not cause phytotoxicity. It not only solves the problem of powdery mildew, but also ensures the normal growth of melons.