Liquid Fertilizers

inorganic substances, produced industrially and introduced into the soil in a liquid state. Liquid fertilizers include nitrogenous fertilizers, anhydrous liquid ammonia, aqueous ammonia, ammoniates, concentrated solutions of ammonium nitrate and urea, and complex fertilizers containing two or three basic plant food elements (nitrogen, phosphorus, and potassium) in various proportions.

In the USSR nitrogenous liquid fertilizers began to be used in 1956; in 1969 approximately 3 million tons of liquid fertilizer were used on kolkhoz and sovkhoz fields. The experimental industrial manufacture and use of complex fertilizers began in 1966. Liquid fertilizers are extensively used abroad. In the USA up to 50 percent of the nitrogenous fertilizers and about 10 percent of the complex ones are applied as liquids. Nitrogen liquid fertilizers are used in Czechoslovakia, Denmark, and other countries, and complex liquid fertilizers are used in France, Great Britain, and Canada.

Nitrogenous liquid fertilizers (ammonia solution 16.5–20.5 percent, anhydrous liquid ammonia 82.2 percent, ammonia liquors 35–45 percent) contain nitrogen mainly or exclusively in the form of ammonia (NH;}), which bonds firmly with the soil particles and is not washed out by rain or melted snow water. Thus, liquid fertilizers can be applied not only in spring but also in late summer (under a winter crop) and in the autumn (under the following year’s spring crop). Liquid fertilizers are introduced into the soil to a specific depth (to avoid ammonia loss) by trailer or tractor-mounted machines with plows or cultivators. Ammonia solution and liquors are introduced at a depth of 10–12 cm, and anhydrous liquid ammonia at 15–20 cm (depending on the mechanical state of the soil). Since ammonium nitrate and urea solutions (up to 30–32 percent) do not contain ammonia, they can be put in the top dressing and sprayed over the soil’s surface. Liquid fertilizer doses (in terms of nitrogen) are the same as those of solid nitrogen fertilizers.

Liquid fertilizer containing free ammonia is stored and transported in air-tight vessels. Steel tanks that can with-stand high vapor pressure reaching 2 meganewtons per sq m (20 atmospheres) are used for anhydrous ammonia. Tanks used for tractor fuel are suitable for aqueous ammonia. Ammoniates require vessels that are made of stainless steel, aluminum, or plastic or have an anticorrosion coating. Nitrogen liquid fertilizers are considerably cheaper than solid ones, and less labor is needed to apply them.

Complex liquid fertilizers are aqueous solutions containing up to 27 percent nitrogen, phosphorus, and potassium. With stabilizing additives (colloidal clay, bentonite) to prevent crystallization, it is possible to increase the concentration of food substances in the fertilizer to 40 percent. Since complex fertilizers do not contain free nitrogen they can be applied to the surface during plowing, cultivating, or harrowing, and during sowing in a drill row.