-
Why nutrients have been depleted from soil.
-
What sources of plant food can be used to help the plants
grow and produce.
-
How to tell what a plant needs. Soil testing, leaf samples,
etc.
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Determination of the kinds and quantities of fertilizers
required by crops.
-
When is the best time for the application of plant food.
-
Fertilizer application methods.
-
Crop production practices used for better utilization
of available nutrients in the soil.
Introduction:
All living things require food to sustain life (#1).
The kinds of food that different living things need to stay
alive is important for their health. People need foods such
as corn, beans, tomatoes, carrots, and meat (#2). Animals
need grasses and grain (#3).
Plants, on the other hand, get the food they need from the
soil they grow in, the air around them, and the water in the
soil (#4).
If there is not enough food or there is not the right kind
of food, people as well as plants may become weak and unhealthy,
and some will eventually die (#5).
Concept 1:
Why nutrients have been depleted from soil.
Plants have been grown on the soil for many, many, years
so people could have food. The food that plants use to grow
is beginning to run out from the soil and the plants become
smaller and smaller and weaker and weaker (#6). It is just
like going to the store or market and finding all the shelves
and tables bare, and nothing else to buy.
But plants can be made well and strong just like people if
they are fed the right things, at the right time, and in the
right way(#7).
The plant food we use is applied to the soil, so the roots
can take it into the plant and it is moved inside the plant
where needed (#8-9).
Concept 2:
What sources of plant food can be used to help the plants
grow and produce.
Plant foods may come from different sources. They may come
from animal manures. They may come from plant roots, stems
and leaves that died and are left in the soil. Or they can
be bought at the store--in bags of plant food or fertilizer
(#10).
But no matter where the plant foods come from, they must
supply what the growing, living plant needs and is not getting
from the soil.
Concept 3:
How to tell what nutrient plants need. Soil testing, leaf
samples etc.
How can you tell by looking at a growing plant what is needed
to feed it properly? Often that is very difficult, and the
best way to tell what a plant needs is to look at what food
is available in the soil for it to use. This could be accomplished
with a soil test. This kind of test tell us if there is not
enough of any nutrient a plant needs.
Soil testing, however, is not often available to many small
farmers. So we must look at the growing plant to see how healthy
it is and look for signs of stress on its leaves and stems
(#11).
If you see the following things about a plant it might be
caused by the lack of a plant nutrient (#12).
Nitrogen-deficiency plants seem normal but are small, weak
looking, and generally light yellow.
Phosphorous-deficiency plants look reddish or purple at older
leaves on a normal green plant. Plants also mature very late.
Potassium-deficiency plants will have a yellow or tan dry
look on older leaf edges.
Be aware that most of the time detecting a deficiency by
sight may be too late to cure. Usually damage to crop yield
has been done. The application of nutrients may not be much
good at this time, especially on slow releasing compounds
such as phosphates.
These nutrients will be the ones that plants will most often
use up over the years and are lacking in the soil.
Concept 4:
When is the best time for the application of plant food.
If you see some of these signs in your plants, how can you
give what is needed to make the plant healthy? Except for
nitrogen (N), there is little that can be done during the
cropping season. Most of the major plant nutrients except
nitrogen need to be put on the soil before the crop is planted.
Nitrogen may be applied before planting, after planting, and
during plant growth (#13).
Concept 5:
Crop production practices used for better utilization of
available nutrients in the soil.
What plant food can you use to make plants healthy?
For many farmers there are not many choices. Farmers must
consider animal manures or buy fertilizer in bags from a store.
This sometimes is either not available or too costly. Something
that every farmer can do--especially if he grows beans and
corn, for instance--is to use crop rotation (#14).
In crop rotation we plant beans and corn on the land one
year. Then the next year, plant the beans where the corn was
and the corn where the beans were. Rotations are good for
your soil and should be used all the time.
As you are rotating crops, you can also add fertilizer to the
crop. Fertilizer bought in bags in the store is easiest to use.
If you have access to manures, you can mix the fertilizer into
the manure and add the mixture to the crop. Remember that the
numbers on the bag of fertilizer tell you how much actual plant
nutrient you have (#15).
If you use a common fertilizer on corn, nitrogen probably
will be the most important crop nutrient to add in first.
Some nitrogen could be added at planting time. Also, when the
corn is knee high and just before tasseling (#16).
If you use a common fertilizer on beans, phosphorous will
probably be the most important crop nutrient to add in first.
Phosphorous should be placed in the bottom of where the seed
is to be planted. Then a little soil put over the phosphorous
and followed by placing the beans and covering them with soil.
Phosphorous needs to be below the bean seeds or any other
seeds it is used on, even corn. But, should not be in direct
contact with the seed to avoid damage (#17).
The amount of fertilizer to use with your crops will be discussed
with each crop in other lessons.
List of figures for lesson 1.5
(Click on the numbered links below to view and print
full-sized figures)
 1. Drawing of tree, corn, people, cereal,
bird, and horse.
2. People at meal with specific foods.
3. Annual grazing plants.
4. Plant food in soil, soil line.
5. Sick person, sick animal, sick plant.
6. Healthy plant, less healthy.
7. Draw plant broadly.
8. Drawing of plant showing N, P, K, Ca moving
to different parts.
9. Show nutrient swarm.
10. Drawing of fertilizer bag, manure, and
plants decomposing.
11. Drawing of man looking a plant sample.
12. Drawing of deficiency symptoms for N,
P, K.
13. Drawing of farmer fertilizing crop.
14. Drawing of crop rotation.
15. Drawing of a fertilizer bag.
16. Drawing of when to fertilize corn.
17. Drawing of where to apply phosphorous
fertilizer.
Lesson 1.5 Notes
SOIL FERTILITY AND CROP PRODUCTIVITY
Soil is a natural body made up of finely divided rock and
mineral particles mixed with varying amounts of humus and
plant residues. From the fertility standpoint, the humus and
smallest mineral particles (clay) are the most important parts
of soil. The silt and sand grains contribute little toward
fertility; but they help provide good tilth, necessary aeration,
and favorable water intake rates. No other natural or artificial
body provides such an ideal reservoir for holding and releasing
water and plant foods for crop growth. At the same time, the
soil provides a porous bed to anchor and feed plant roots.
Will Soil Last Forever?
Soils age and change gradually. A particular soil will likely
not be the same a thousand years from now. The soils in areas
of the world where people have lived for thousands of years
have also been growing crops to feed people. The soils no
longer have the nutrient supplying capacity they once had
and therefore must be enriched by having plant nutrients added
to them for the crops they are to grow. Good soil productivity
can be preserved indefinitely by good soil husbandry.
FERTILIZER PRODUCTS; THEIR DESCRIPTION AND USE
What is Fertilizer?
A fertilizer is a material containing one or more plant nutrients
that can be added to the soil to make the soil more productive.
To fertilize a soil means to enrich it. Fertilizer is added
to soil to insure against a shortage of plant nutrient elements
which would limit crop growth. Commercial products containing
the essential plant nutrients or plant foods are referred
to as commercial fertilizers. Used wisely, fertilizers increase
soil fertility, replace the nutrients removed in harvested
crops, and maintain high plant nutrient levels in the soil.
To provide adequate levels of plant nutrients in the soil
and maintain and increase crop production, fertilizer use
must be greatly increased. It is also important to understand
that proper crop rotation can improve soil nutrients. Animal
manures and crop residues (leaves, stems, roots) left or put
in the soil are also sources of plant nutrients for growing
crops.
What is a commercial fertilizer?
A commercial fertilizer is one that is manufactured and sold
with specific amounts of plant nutrients specified on the
container. The amount of fertilizer material is always expressed
in % of each element present. The major elements N, P, and
K are always listed in that order. This listing of available
plant nutrients establishes what is known as fertilizer "grade."
A fertilizer grade gives the minimum content of primary plant
nutrients in terms of percent and is expressed as:
N total nitrogen
P2O5 available phosphate
K2O water soluble potash
A grade may contain one or more of the three primary plant
foods. A grade which contains only one is called a single
carrier or sometimes a straight material. Examples of single
carriers are ammonium nitrate (33-0-0), concentrate superphosphate
(0-45-0) and sulfate of potash (0-0-50). Examples of mixed
fertilizer are 10-10-10, 30-10-0, and 16-20-0. 11-48-0. The
difference in weight between the total plant nutrients in
the bag and the total weight of the bag is made up of material
such as clay that act as a carrier or filler for the fertilizer.
For instance, a bag of 33-0-0 weighing 22 kg would contain
7.26 kg of N and 14.7 kg of filler material.
Why aren't fertilizers 100% plant foods?
Plants cannot use nutrients in the pure elemental form such
as nitrogen (N), phosphorus (P), or potassium (K). In the
elemental form nitrogen is a gas not available for plant use.
Four-fifths of the air we breathe is nitrogen in the elemental
form. Phosphorus (P) cannot be handled in the elemental form,
because it ignites when exposed to air. Similarly, potassium
burns when it contacts water. For these reasons it is necessary
to fertilize with compounds of the nutrient elements.
Where do the raw materials for fertilizers come from?
Nitrogen fertilizers are processed largely from nitrogen
in the air which is combined with hydrogen to make ammonia
(anhydrous ammonia). Ammonia may then be further processed
to make ammonium nitrate, urea, ammonium phosphates, ammonium
sulfate, and other fertilizers.
Phosphate fertilizers are obtained principally from
a phosphate rock, called fluorapatite. Phosphate rock contains
about 30-35% phosphate (P2O5), but all of this is in a form
that plants cannot use. Raw rock phosphate must be treated
with strong acids to remove undesirable elements and make
the phosphate available for plant use. After the rock ore
has been treated with acids, calcium phosphate and phosphoric
acid are obtained. The phosphoric acid--or so called "phos-acids"--may
be treated with ammonia to make several different grades of
"ammo-phos" fertilizers. In recent years, highly purified
and concentrated "polyphosphates" have been produced. These
new polyphosphates contain 65-85% available phosphate (P2O5).
They can be used to make high grade amorphous fertilizers--both
granular and liquid materials.
Potash (K2O). Potassium. Potash comes primarily from
mining in South America, Canada and Germany. The remaining
amount comes from the U.S. and Europe. Most of the potassium
mines are developed in naturally occurring chloride and sulfate
salts. These are refined or upgraded to satisfy fertilizer
requirements. Much of the potash fertilizer sold is in the
form of potassium chloride (KC1)--"Muriate of Potash." The
remainder is mostly potassium sulfate (K2SO4)--"sulfate of
potash."
Secondary plant foods--Calcium (Ca), Magnesium (Mg),
and Sulfur (S). These materials have minor roles as fertilizer
ingredients but are critical when needed. Most soils of arid
regions contain adequate calcium and magnesium. Sulfur deficiencies
will probably be restricted to localized areas. Sulfur is
often present as sulfate (SO4) in fertilizers like ammonium
sulfate, (21-0-0), ammonium phosphates (including 16-20-0)
and single superphosphates (0-20-0).
Micronutrients. The micronutrients can be used in
various forms including sulfates, oxides, and chelates. Zinc
(Zn), copper (Cu), manganese (Mn), and iron (Fe) are most
frequently combined with sulfates, and as such they are readily
soluble in water. Boron (B) and molybdenum Mo) are usually
sold as sodium borates or sodium molybdates, respectively.
Plant Foods Utilized by Various Crops and Sources of Supply
From the information in Table 1, it is easy to see why after
thousands of years of continuous cropping the soil would begin
to be depleted of plant foods. It is therefore necessary to
add materials into the soil to help crops grow and be healthy.
The amount of plant food (fertilizer) that will be needed
will depend on the crop that is grown and various management
factors associated with the crop. These things will be discussed
as part of the production package for each crop.
| Table 1. Plant Food Utilization
by Various Crops* |
| Crop |
Yield |
N (lbs./acre) |
P2O5 (lbs./acre) |
K2O (lbs./acre) |
| Field crops |
|
|
|
|
| Barley |
2.5 t. (104 bu) |
160 |
60 |
160 |
| Corn (grain) |
5 t. (179 bu) |
240 |
100 |
240 |
| Corn (silage) |
30 t. |
250 |
105 |
250 |
| Dry bean |
|
115 |
10 |
50 |
| Cotton (lint) |
1,500 lbs. |
180 |
65 |
125 |
| Grain Sorghum |
4 t. (143 bu) |
250 |
90 |
200 |
| Oats |
3,200 lbs. (100bu) |
115 |
40 |
145 |
| Rice |
7,000 lbs. |
110 |
60 |
150 |
| Safflower |
4,000 lbs. |
200 |
50 |
150 |
| Soybeans |
3,600 lbs. (60 bu) |
325 |
65 |
145 |
| Sugar beets |
30 t. |
255 |
60 |
550 |
| Wheat |
3 t. (100 bu) |
175 |
70 |
200 |
| Vegetable crops |
|
|
|
|
| Asparagus |
3,000 lbs. |
95 |
50 |
120 |
| Beans (snap) |
10,000 lbs. |
175 |
40 |
200 |
| Broccoli |
18,000 lbs. |
80 |
30 |
75 |
| Cabbage |
35 t. |
270 |
65 |
250 |
| Celery |
75 t. |
280 |
165 |
750 |
| Lettuce |
20 t. |
95 |
30 |
75 |
| Potatoes (Irish) |
500 cwt |
270 |
100 |
550 |
| Squash |
10 t. |
85 |
20 |
120 |
| Sweet potatoes |
15 t. |
155 |
70 |
315 |
| Tomatoes |
30 t. |
180 |
50 |
340 |
| Fruit and nut crops |
|
|
|
|
| Almonds (in shell) |
3,000 lbs. |
200 |
75 |
250 |
| Apples |
15 t. |
120 |
55 |
215 |
| Cantaloupes |
30 t. |
220 |
70 |
400 |
| Grapes |
15 t. |
125 |
45 |
195 |
| Oranges |
30 t. |
265 |
55 |
330 |
| Peaches |
15 t. |
95 |
40 |
120 |
| Prunes |
15 t. |
90 |
30 |
130 |
| Forage crops |
|
|
|
|
| Alfalfa |
8 t. |
480 |
95 |
480 |
| Bromegrass |
5 t. |
220 |
65 |
315 |
| Clovergrass |
6 t. |
300 |
90 |
360 |
| Orchardgrass |
6 t. |
300 |
100 |
375 |
| Sorghum-sudan |
8 t. |
325 |
125 |
475 |
| Timothy |
4 t. |
150 |
55 |
250 |
| Vetch |
7 t. |
390 |
105 |
320 |
| Turf crops |
|
|
|
|
| Bentgrass |
2.5 t. |
260 |
65 |
145 |
| Bermudagrass |
4 t. |
225 |
40 |
160 |
| *Total uptake in harvest
portion. |
Table 2 shows the value of animal manures as fertilizer for
crop plants.
While the amount of any given nutrient is quite low in even
a large volume of manure, still the addition of manure to
the soil of even small amounts is helpful for the plant.
| Table 2. Nutrient Content of Livestock
Manures |
| Manure Source |
N |
P2O5 |
K2O |
| % |
kg/Mt |
% |
kg/Mt |
% |
kg/Mt |
| Beef (feedlot) |
0.71 |
14.2 |
0.64 |
12.8 |
0.89 |
17.8 |
| Dairy cattle |
0.56 |
11.2 |
0.23 |
4.6 |
0.60 |
12.0 |
| Hog |
0.50 |
10.0 |
0.32 |
6.4 |
0.46 |
9.2 |
| Horse |
0.69 |
13.8 |
0.23 |
4.6 |
0.72 |
14.4 |
| Sheep |
1.40 |
28.0 |
0.48 |
9.6 |
1.20 |
24.0 |
| Chicken (no litter) |
1.56 |
31.2 |
0.92 |
18.4 |
0.42 |
8.4 |
| Table 3. Common Commercial Fertilizer
Formulations |
|
%N |
%P2O5 |
%K2O |
| Urea 46-0-0 |
46 |
0 |
0 |
| Ammonium Nitrate 34-0-0 |
34 |
0 |
0 |
| Ammonium Sulfate 21-0-0 |
21 |
0 |
0 |
| Treble Superphosphate 0-46-0 |
0 |
46 |
0 |
| Potassium Chloride 0-60-0 |
0 |
60 |
0 |
| Mixed 16-16-16 |
16 |
16 |
16 |
| Mixed 18-18-18 |
18 |
18 |
18 |
| Mixed 16-20-0 |
16 |
20 |
0 |
| Diammonium Phosphate 18-46-0 |
18 |
46 |
0 |
| Monoammonium Phosphate 11-48-0 |
11 |
48 |
0 |
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