   Organic Fertilizers - March 15, 2000 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County As you prepare for spring planting, think about the nutritional needs of the crops you will plant. Unlike other plants in our landscapes, most vegetables and flowers are annual plants (i.e., they germinate, grow, and produce fruit or seed in one year or less). Furthermore, vegetables and annual flowers are not well adapted to our local climate. If we expect them to perform well, then we must give them all of the nutrients they need prior to planting. Increasingly, backyard vegetable growers are using organic fertilizers. Organic fertilizers supply the same essential plant nutrients as manufactured (non-organic) fertilizers. The major differences are in their availability and concentration. Manufactured fertilizers contain nutrients that are available immediately and highly concentrated. Conversely, organic fertilizers are not as readily available and less concentrated. To become available, they require moisture, warm soil temperatures (50 degrees F or greater), and some assistance from resident soil microorganisms to release the nutrients they contain. For vegetables and flowers, nitrogen and phosphorus are the most critical nutrients for garden success. Nitrogen is needed for all stages of growth and development. Phosphorus is needed for juvenile root growth and reproduction (flowering and fruiting). Manufactured fertilizers most often contain only the essential plant nutrients listed on the container. Organic fertilizers often contain small amounts of other nutrients that may or may not be listed specifically on the container. Think about it: organic fertilizers come from recycled plant and animal wastes. Those plants and animals consumed and contained many nutrients other than nitrogen, phosphorus, and potassium to survive. Before we start reviewing individual materials, remember the three numbers on a fertilizer package stand for percent composition (guaranteed analysis) of nitrogen, phosphorus, and potassium (N-P-K). Don=t worry about potassium because we generally have adequate amounts in our native soil. My personal preference is to use separate materials to supply additional nitrogen and phosphorus. I add nitrogen fertilizer to the entire row or bed and to place phosphorus fertilizer strategically close the root zone (banding). There are several choices available for organic nitrogen fertilizers. I have included approximate guaranteed analysis figures for each material. Blood meal (13-1.5-0), hoof and horn (14-0-0), fish emulsion (5-1-1), and fish scrap (9-7-0) are made from animal by-products. Plant-based materials include cottonseed meal (6-2.5-2), alfalfa meal (2.5-0.5-2), and kelp meal (1-0.5-9). Manures are also an excellent source of nitrogen. Some commercially available manures are from cattle (0.5-0.3-0.5), horse (0.6-0.3-0.5), sheep (0.9-0.5-0.8), and chicken (0.9-0.5-0.8). Human waste is also available, but not recommended for vegetable gardens (unless you are very familiar with the source). Bat guano (6-9-3) and bird guano (13-11-2) are high in phosphorus (and tend to be expensive due to harvesting practices and shipping distances). Rock phosphate (0-3-0) and bone meal (4-22-0) contain moderate amounts of phosphorus but are not very soluble in our alkaline soils. If you use either of these products, it is critical to band them near the roots and mix them with soil sulfur to help acidify the band. Organic fertilizers can provide the nutrients plants need if applied correctly. It is difficult to add too much organic fertilizer and easy to add too little. If using uncomposted manure, incorporate it into the soil several weed prior to planting to let the microorganisms start to break it down. When deciding on an organic fertilizer, calculate the cost per pound of nitrogen or phosphorus. For example, if a five-pound bag of blood meal (13-1.5-0) costs $8.00, then the entire bag contains 0.65 pounds of nitrogen ($12.31 per pound). This may help you choose the organic fertilizer to purchase. More likely, it will convince you to borrow a truck, haul manure from the stable, and build a huge compost pile and worm bed. The University of Arizona Cooperative Extension has publications and information on vegetable gardening and composting. Also visit our web site at (http://ag.arizona.edu/yavapai/). If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. |