Phosphorus needs of plants
Phosphorus is important in forming root tissues. Phosphorus is very important in establishing seedlings, and then as plant matures about 50 to 75% of the plants' phosphorus is in the root. It is also known to be important for the development of fruit (Sprague). Phosphorus is needed to form many protein complexes.
Phosphorus deficieny in plants
< Phosphorous deficiency in corn shows as a purple cast
Phosphorus deficiency usually shows up first in older leaves and tissues. When phosphorus is deficient it can leave a dark purple cast to undersides of leaves and veins. The roots are also often poorly developed, and may have rusty brown lesions or spots in interior tissues. It also causes a black or brown inter-veinal necrosis and leaves curl upwards. With a phosphorus deficiency, fruit is small.
It is very important to root crops. A deficiency inhibits fruiting and causes a dark or purplish discoloration of leaves. P:N and P:Fe are both crucial. PO4+++ is available to plants. Only dissolved is available and in alkaline media it precipitates most phosphate as calcium or magnesium salts. Excess phosphorus precipitates with iron, reducing available iron. It becomes a part of many important organic compounds.
Phosphorus can become unavailable in high acid conditions, or dry media or soils. It should be at 200-300 ppm availability for plants and under 125 ppm it is probably deficient.
Phosphorus needs for humans
It is the second most abundant element in body 80-85% in bones. Bone undergoes remodeling and turnover.
A calcium:phosphorus ratio is important to a balanced diet recommended as 2:1 or 2.5 to 1( Kirschmann, J.D., 1975. The ratio is needed for minerals to be efficiently used by the body. Niacin and riboflavin cannot be digested without phosphorus.
About 70% of ingested phosphorus is absorbed by the body, but vitamin D and calcium must also be present for absorbtion. Insoluble phosphates can be formed with iron, aluminum and magnesium. About 800 mg/day is recommended, and an equal amount of calcium (Kirschmann, J.D., 1975).
Most calcium absorbed is stored in teeth and bones.
Blood plasma is 9 to 12 mg/ 100 g calcium. Whole blood is 35 to 45 mg P per 100 ml mostly in cells with phosphorus 4 to 9 per 100 ml in plasma. There is a continuous process of interchange of calcium and phosphorus between bone, blood supply and other parts of the body. Phosphorus is concentrated in the red blood cells, muscle and nerve tissues.
Phosphorus needs in animals
In horses, a phosphorus deficiency results in loss of appetite, which results in a craving for and chewing of bones, wood, hair, rocks, clothing and other materials.
Phytins are unavailable
Certain phosphorus compounds, phytins, are excreted unchanged. In cereals, total phosphorus content is not a correct measure of available available phosphorus. Phytin is also capable of depleting body of other minerals if a digestive enzyme is not present.
Some of the phosphorus content of foods may be unavailable for some people. Phytic acid on the outer husks of beans and grains is a digestive problem for people who lack a digestive enzyme called phytase. Phytic acid binds with calcium, magnesium and iron. Sprouting and leavening neutralizes the effects of phytic acid. Soaking beans and peas in water breaks down some phytic acid, but cooking does not.
Table 42 - Phytin content of foods containing phosphorus (McCance et al. 1935).
Food items |
Total P |
Phytin |
|
mg/100g |
mg/100g |
Barley, pearled |
354 |
78 |
Barley whole |
335 |
211 |
Bread brown |
198 |
82 |
Wholemeal |
237 |
87 |
Flour white |
102 |
15 |
Flour wholemeal |
355 |
166 |
Maize yellow |
363 |
210 |
Millet whole |
350 |
191 |
Oats w husk |
350 |
182 |
Rice polished |
99 |
41 |
Rice unpolished |
350 |
240 |
Beans, baked |
184 |
27 |
Beans broad boiled |
108 |
5.4 |
Beans butter, raw |
318 |
147 |
Haricot, raw |
309 |
154 |
Lentils |
243 |
93 |
Peas fresh |
105 |
11 |
Peas split |
268 |
124 |
Peanuts |
365 |
220 |
Carrots |
20 |
3.3 |
Jersalem articokes |
37 |
9.2 |
Potatoes, new boiled |
35.7 |
8.2 |
|