بازدهی استفاده کود فسفره(زبان اصلی)

[محمد بهبود]

Essential Role Of Phosphorus (P) In Plants
Phosphorus is an essential nutrient both as a part of several key plant structure
compounds and as a catalysis in the conversion of numerous key biochemical reactions
in plants. Phosphorus is noted especially for its role in capturing and converting the
sun’s energy into useful plant compounds. The two examples that follow illustrate how
vital phosphorus nutrition is to normal plant development and production.
Phosphorus is a vital component of DNA, the genetic "memory unit" of all living things. It
is also a component of RNA, the compound that reads the DNA genetic code to build
proteins and other compounds essential for plant structure, seed yield, and genetic
transfer. The structures of both DNA and RNA are linked together by phosphorus
bonds.
Phosphorus is a vital component of ATP, the "energy unit" of plants. ATP forms during
photosynthesis, has phosphorus in its structure, and processes from the beginning of
seedling growth through to the formation of grain and maturity.
Thus phosphorus is essential for the general health and vigor of all plants. Some
specific growth factors that have been associated with phosphorus are: stimulated root
development, increased stalk and stem strength, improved flower formation and seed
production, more uniform and earlier crop maturity, increased nitrogen N-fixing capacity
of legumes, improvements in crop quality, and increased resistance to plant diseases.
Phosphorus deficiency is more difficult to diagnose than a deficiency of nitrogen or
potassium. Crops usually display no obvious symptoms of phosphorus deficiency, other
than a general stunting of the plant during early growth, and by the time a visual
deficiency is recognized it may be too late to correct in annual crops. Some crops, such
as corn, tend to show an abnormal discoloration when phosphorus is deficient. The
plants are usually dark bluish-green in color with leaves and stem becoming purplish.
The degree of purple is influenced by the genetic makeup of the plant, some hybrids
showing much greater discoloration than others. The purplish color is due to
accumulation of sugars which favors the synthesis of anthocyanin (a purplish colored
pigment) that occurs in the leaves of the plant.
Phosphorus is highly mobile in plants and when deficient it may be translocated from
old plant tissue to young actively growing areas. Consequently, early vegetative
responses to phosphorus are often observed. As a plant matures, phosphorus is​

Efficient Fertilizer Use —

Phosphorus: Dr. Bill Griffith​

2​

Soil Temperature/Aeration/Moisture and Compaction​

Phosphorus absorption by the plant is decreased by low soil temperature and poor soil​

aeration. Starter fertilizers containing water-soluble phosphorus are much more likely to​

Efficient Fertilizer Use — ​

Phosphorus: Dr. Bill Griffith​

5​

increase crop growth during cool weather. Excessive soil moisture or soil compaction​

reduces the soil oxygen supply and decreases the ability of the plant roots to absorb soil​

phosphorus. Compaction reduces aeration and pore space in the root zone. This​

reduces phosphorus uptake and plant growth. Compaction also decreases the soil​

volume that plant roots penetrate, limiting their total access to soil phosphorus.​

Soil Test Phosphorus Levels​

Crop responses to fertilizer phosphorus will be greater and occur more frequently on​

soils testing low in phosphorus than on high testing soils. However, yields on soils with​

high P soil test levels usually are higher. The response to phosphorus fertilizer on high​

testing soils is increasing and it is important to maintain high soil phosphorus levels to​

support optimum crop production.​

Fertilizer Phosphorus Management Considerations​

Conservation Tillage​

Conservation tillage practices are increasing. Factors associated with the various​

conservation tillage practices are a lower soil temperature at planting, a higher soil​

moisture content, an increased possibility of soil compaction, and an accumulation of​

soil acidity near the soil surface. Each of these factors increase the possible response​

of fertilizer phosphorus, especially starter phosphorus. This occurs even at high soil test​

levels. Adequate phosphorus fertilization is essential for rapid early growth and high​

yields when using conservation tillage systems. Responses to applied phosphorus at​

high soil test levels have been noted in numerous research studies conducted on​

several crops.​

Table 6.2: Response to Applied Phosphorus at High Soil Test Levels​

Yield​

Location Crop​

Soil​

Test​

P Level Without P With P​

Louisiana Cotton High 949 1,073 lb/acre lint​

Arkansas Cotton High 1,402 1,638 lb/acre lint​

South​

Dakota Corn High 124 145 bu/acre​

Wisconsin Corn High 122 149 bu/acre​

Minnesota Corn High 89 100 bu/acre​

Kansas Wheat High 23 41 bu/acre​

New York Barley High 70 100 bu/acre​

Efficient Fertilizer Use — ​

Phosphorus: Dr. Bill Griffith​

6​

Early Planting​

Earlier planting dates for corn and some other crops increase yield potential. More and​

more farmers can benefit from this advantage as they have upgraded equipment and​

reduced the number of trips over the field prior to planting. Earlier planting dates means​

cooler soils and less movement of soil phosphorus and a higher potential for response​

at high soil test levels.​

Soil Drainage​

Crops on poorly drained soils often show phosphorus response even at high soil test​

levels. Low oxygen availability in poorly drained soils reduces root growth rates and​

limits their ability to absorb and translocate phosphorus. The higher soil moisture​

content also tends to keep these soils cooler in the spring, further reducing phosphorus​

uptake.​

Balanced Nutrition​

Balanced nutrition is a must for realization of the full phosphorus response potential of​

crops. Insufficient levels of other nutrients can substantially reduce response to​

phosphorus. For example, a long-term Kansas study showed that response of irrigated​

corn to phosphorus continually increased with increasing nitrogen rate until the optimum​

nitrogen level was reached. Using soil tests to maintain adequate levels of all nutrients​

plus lime requirements helps maintain phosphorus efficiency.​

Table 6.3: Response Of Irrigated Corn To Phosphorus​

Annual P​

2O5, lb/acre​

Annual​

N Rate 0 40​

Average​

Response​

lb/acre​

(10-Year Average Corn Yield,​

bu/acre) bu/acre​

Phosphorus Placement​

If a grower is looking for maximum return from high phosphorus investment on low​

testing soils, band application is best. Where conservation tillage is practiced,​

combinations of both band and broadcast applications of phosphorus may be needed.​

This insures an early, accessible phosphorus supply for developing seedlings and a​

nutrient reserve later in the growing season when phosphorus demands remain strong.​

Efficient Fertilizer Use — ​

Phosphorus: Dr. Bill Griffith​

7​

Several advantages for broadcast/plowdown phosphorus applications are; (1) High​

rates can be applied without injuring the plant; (2) Nutrient distribution throughout the​

root zone encourages deeper rooting, while band placement causes root concentration​

around the band; (3) Deeper rooting permits more root-soil contract, providing larger​

reservoir of moisture and nutrients; (4) A practical way to apply fertilizer to forages; and​

(5) Helps insure full-feed fertility to help the crop take full advantage of favorable growth​

conditions throughout the growing season.​

Dual application of anhydrous ammonia and ammonium polyphosphates at seeding of​

wheat has been found to be superior to broadcast or band applications of ammonium​

polyphosphates.​

Placement directly under the drill row (band seeding) for forage crops has proven​

superior to broadcast or side placement. Tomatoes and onions have responded best to​

phosphorus placed directly below the seed or set.​

Diammonium Phosphate (DAP) 18-46-0​