Cow Manure and Yellow Tomato Leaves

Fresh vs. Composted Manure

• While cow manure is largely good for plants, fresh manure isn't. Fresh manure contains extremely high amounts of nitrogen and ammonium as well as pathogens and bacteria, like E coli, which are all dangerous to plants. If these toxins make direct contact with tomato plant leaves, they burn and turn them yellow. Rather than enhance plant growth, fresh manure actually prevents germination, damages roots and discolors foliage, which results in diminished crop yields. Only use composted manure that has been aged six months or longer on tomato plants.

Composting

• There are two basic ways to compost manure: spread it on soil after the fall harvest or hot compost it. Selecting a method is typically a matter of preference; each one is effective. Apply a layer of fresh manure over the soil after you harvest the last crop of tomatoes in the fall. About one month before you plant tomatoes in the spring, incorporate the manure with the soil so that the now decayed manure thoroughly combines with the top 6 inches of soil. The alternative is to hot compost manure by letting fresh shallow heaps of manure rest for six months. The pile naturally heats to about 150 degrees Fahrenheit -- hot enough to burn off some of its nitrogen and ammonium content, in addition to harmful pathogens. Once it has been sufficiently aged, it's ready for use with tomato plants.

Nutrient Levels

• Although a cow's diet ultimately determines the exact nutrient amounts of its manure, on average a dairy cow's manure has nitrogen, phosphorous and potassium (NPK) levels of 25-15-25. The NPK rate is generally lower than the rates of chicken, sheep and steer manures. Cow manure's low NPK rate is also what makes it such a safe and versatile fertilizer for garden use. Use composted manure in unrestricted quantities to enrich soil and as topdressing.

Liquid Cow Manure

• Liquid cow manure provides the advantages of composted manure without the need to complete the aging process. It's available at most nurseries and garden centers in a concentrate form. Use it on tomato plants to increase nutrient intake. Plant roots are able to absorb the liquid quicker than composted manure matter and thus reap the benefits sooner.