Solid Forms of Nitrogen That Plants Can Take Up

Process

• Plants take up nitrogen dissolved in water when they absorb water through their roots and root hairs. When solid sources of nitrogen are applied to the soil -- dead leaves, for example -- the microlife of the soil processes the nitrogen into forms plants can take up, such as nitrate and ammonium. Nitrates move easily through soil moisture, while ammonium ions tend to be held by clay particles.

Byproducts

• Manure from dairy cattle, chickens, goats, llamas and similar animals is a common source for adding solid nitrogen to the soil. Field byproducts such as ground-up cornstalks and other leftovers after a crop has been harvested also add nitrogen when applied to the soil. Compost made from dead plants and vegetable trimmings includes the nitrogen those plants took up from the soil.

Cover Crops

• Planting cover crops in the fall that will be tilled into the soil in early spring is another way to add solid nitrogen to soil. Legumes such as fava beans, field or winter peas, hairy or common vetch and crimson clover fix nitrogen from the atmosphere, forming nodules on their roots. When they are turned under and decay, the nitrogen is released for the crops you plant.

Ammonium Nitrate

• Ammonium nitrate comes in granulated form and is most often used as an agricultural fertilizer, although it also is an ingredient in pelleted fertilizers formulated for the home garden. It has a 34 percent nitrogen content. Sprinkle it onto the surface of the soil and use a cultivator or garden rake to scratch it in. Water the area after applying. Ammonium nitrate is a favored solid nitrogen source for citrus.

Other Sources

• A byproduct of coke ovens, which remove ammonia from coal using sulfuric acid, ammonium sulfate is a solid nitrogen source that is 21 percent nitrogen. Other sources of solid nitrogen for plants include urea, 46 percent nitrogen; calcium nitrate, 15.5 percent nitrogen; and Cal-Nitro, a blend of calcium nitrate and ammonium nitrate, which is 26 percent nitrogen.