AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335
Fall 2001, No. 8
CROPS NEED PHOSPHORUS ALL SEASON LONG
If crops could talk, what would they say about phosphorus? For sure, their position would be clear on at least two issues. The first is that they are capable of helping to resolve some of the issues relating phosphorus with the environment. Secondly, they would advise us of their requirements for a readily available source of phosphorus from their seedling stage to their approach to maturity.
Determining crop need for supplemental phosphorus has changed little during the era of environmental concern. Sources available and timing and method(s) of application have changed some and are under continued assessment … for their interaction with the environment and for their success in meeting crop needs for growth and quality. The management objective for phosphorus should be to establish a crop’s need and then deliver that need in an agronomic, economic, and environmentally sound manner. It can be done.
A first step is to properly sample and analyze the soil from each site-specific management zone in a field. The soil test becomes the foundation upon which the phosphorus recommendation is built. It provides a measure of phosphorus in the soil reservoir that is normally available to a growing plant. However, availability can be altered by several soil conditions and crop management practices. Following are a few points that deserve attention in the development of site-specific phosphorus recommendation for a crop.
Thus, soil tests alone cannot establish crop needs for phosphorus. They must be coordinated to fit with other key crop management practices. Research has documented why phosphorus is an essential component of every crop nutrient management plan. It allows seedlings to develop rapidly and give early ground cover. It helps to generate the huge quantity of crop residue essential for a successful conservation tillage program. It aids in the efficient use of nitrogen, water, and other crop needs. It manages energy so vital to photosynthesis, sugar movement, seed formation, and other functions essential for optimum crop productivity, profitability, and environmental stewardship.
- An increase in soil acidity can reduce the availability of phosphorus to the crop. Incorporate aglime, if possible, well ahead of the planting season to attain desired soil pH level.
- Root growth restrictions, such as soil compaction or injury from soil insects, can reduce root growth, root exploration of the soil, and crop uptake of phosphorus.
- Conservation or reduced tillage is an excellent practice, but it can result in an increase in soil acidity and an accumulation of phosphorus in the upper layer of soil. These conditions develop over time and can render surface soil phosphorus positionally unavailable during periods of crop drought stress.
- Early planting in heavy residue-covered soils often increases the need for supplemental phosphorus. This is due to the cool, moist soil environment around the seed.
- Nutrient requirements change with plant growth stage and with the level of production. These values are known for most crops. Phosphorus must be readily available to the growing crop from the soil reservoir and from supplemental phosphorus applied from fertilizer sources.
For more information, contact Dr. Noble R. Usherwood, Southeast Director, PPI, 233 Kenilworth Circle, Stone Mountain, GA 30083. Phone: (404) 294-0137. E-mail: email@example.com
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