Gray, Carl

Hipp, Billy W.

Hoverson, Richard R.

Pennington, H. Dale

Welch, Charles D.

Texas A&M University

L-1498
FIELD AND FORAGE CROP FERTILIZATION
IN THE LOWER RIO GRANDE VALLEY
Charles D. Welch, Carl Gray, H. Dale Pennington,
Richard R. Hoverson and Billy W. Hipp*
The Lower Rio Grande Valley is an important agri-
cultural region containing about 1. 5 million acres as
outlined in figure 1. Field and forage crops, vege-
tables, citrus, sugarcane and cattle grazing rangeland
are important agricultural land uses in this region.
SoIl characteristics
Surfac soils vary from coarse sands to clays. Sub-
soils also vary but most are high in clay. Due to low-
ered annual rainfall from east to west and its erratic
distribution, crop yield potential varies greatly in this
region. Most soils are alkaline and many contain free
calcium carbonate. Both physical and chemical soil
prop rties vary throughout the region. Inadequate
drainage, salinity, alkalinity, low nitrogen (N) and
phosphorus (P20 5) are problems which must be over-
come for profitable production in some areas.
Fig. 1. Location of Lower Rio Grande Valley land resource
regions
*Respectively, Extension soil chemists; Extension area agron-
omists; and associate professor, Texas A&M University Re-
search and Extension Center, Weslaco; all in the Texas A&M
University System.
12.12
Table 1. Percentage distribution of Rio Grande Valley soils in
five levels for calcium (Ca), magnesium (Mg), phosphorus (P) and
potassium (K) and five pH ranges (131 samples)
Percentage of samples
at each level for
Soil test Soil pH
level* Ca Mg P K range Percent
VL 0 9 0 Below 5.0 0
L 0 0 9 0 5.1-5.5 0
M 1 13 2 5.6-6.0 1
H 16 99 30 5 6.1-6.5 2
VH 83 39 93 Above 6.5 97
*From Texas Agricultural Extension Service Soil Testing Labora-
tory 1970-72. VL-very low; L-Iow; M-medium; H-high; and
VH -very high.
Soli fertility status
Soil characteristics, past fertilization and cropping
practices account for a WIde range of nutrient levels
throughout the regions. Soil test summary data are
available for each major crop-producing county and
are useful in identifying general soil fertility prob-
lems.
Distribution of soil samples in nutrient levels and
pH ranges is shown in table 1. Nitrogen levels are
not shown but generally are low, except after a fallow
period following a legume or high nitrogen fertiliza-
tion.
Phosphorus is deficient in some soils, but 69 per-
cent of the samples tested high or very high. This in-
dicates that, except for low rates of "starter" phos-
phorus, this nutrient is not always needed. To proper-
ly determine the phosphorus status of soils, test a
Texas Agricultural Extension Service. The Texas A&M University System. Daniel C. Pfannstiel, Director. College Station
Table 2. Rate of N to apply for grain sorghum, cotton and corn
at yield levels and soil conditions
sample from each field. Potassium (K) generally is
adequate in soils of the region, with 98 percent of the
samples testing high.
Rates of Nand P20S for major crops
The wide range in rainfall, soil fertility levels and
cultural and irrigation management practices in this
region causes considerable variation in rates of added
nutrients required for economical production. The
best guides to profitable fertilization are soil tests,
calibrated to express available nutrients, and corre-
lated with crop response and estimates based on re-
sults of previous research. Important criteria for
selecting the profitable rate of each nutrient are (1)
the level of available nutrient in the soil, (2) the ex-
pected yield or production potential and (3) previous
crop and fertilizer history.
Table 2 shows suggested rates of for cotton,
sorghum and corn at three yield levels when cropped
under various conditions. These estimates are based
on previous research and include conditions that have
the greatest influence on response under Rio
Grande Valley conditions.
Rates of P20 S at varying soil test levels and ex-
pected yields for cotton, grain sorghum and corn are
shown in tables 3, 4 and 5. Soil test levels are based
on Texas A&M University methods and calibration.
Unless a relationship has been established between
other methods and those used by Texas A&M labora-
tories, the use of suggested rates is not valid. Due to
the generally high level of soil K, none is needed in
the fertilizer. Any K fertilization should be based on
a deficient soil as indicated from a soil test.
*Can be applied one-half preplant and one-half sidedressed
Crop and yield level
Grain sorghum
Ib.lA.
3000
4500
6000
Cotton
Bales/A.
1
1%
2
Corn
Bu.lA.
60
90
120
Productive soil
that has been
fallow for 6
months or more
o
o
50
o
o
50
o
30
60
Areas cut for level-
ing, very sandy
soils and immediately
following
another crop
50
75*
100*
40
60*
80*
60
90*
120*
Table 3. Application rates of P20S for cotton at three produc-
tion levels
Soil
level %-1 bale/A. * 1% bales/A. 2 bales/A.
VL 30 40 60
L 20 30 50
M 0 20 30
H 0 0 0
VH 0 0 0
*Dryland or limited irrigation
An estimate of expected yield should be based
on past experience, anticipated rainfall and irrigation,
management, cultural practices and other factors that
affect yields. The expected yield should r flect the
best judgement of the producer and his advisors about
the potential for the production system.
Rates of and P20 S for other major crops are
shown in tables 6 through lL To use th stables,
locate the soil nutrient level in the left column and
the production level at the top and read th appropri-
ate rate in the table. For example, in tabl 6, a soil
low (L) in phosphorus with a 6-ton production poten-
tial would show 40 pounds of P20 5 per acre.
Sugarcane is a relatively new crop in the Rio
Grande Valley. Control of available nitrogen is es-
sential for the production of high yields with accept-
able sugar content. The objective in developing a
nitrogen fertilization program is to insure that ade-
quate nitrogen is available during the period of rapid
vegetative growth, but to allow the plant to b come
mildly deficient prior to harvest. Phosphorus is
needed for soils low in this nutrient. However, not
all soils in the Rio Grande Valley need phosphorus
fertilization. It is important to determine from a soil
test or estimate the level of nutrients in the soil prior
to planting or replanting sugarcane. Rates of nitrogen
and phosphorus to consider are shown in table 1L
Potassium has not been shown necessary because of
the generally high soil levels.
More information about sugarcane fertilization
can be obtained from Texas Agricultural Experiment
Station Information Report No. 75-5, Texas Sugar-
cane Growers Guide, available from the Weslaco Re-
search Center.
Potassium, calcium, magnesium and sulfur
Approximately 99 percent of the tested samples
rated high in calcium and magnesium. Thus, de-
ficiencies have not been reported. Calcium and mag-
nesium dominate the clay fractions and are respon-
sible for the alkaline condition (up to pH 8.3) of most
soils. Higher pH values generally are caused by ex-
changeable sodium.
Sulfur occurs in most irrigation water as the sul-
fat ion and deficiencies have not been identified on
crops in the Rio Grand Valley.
Mlcronutrients
Som micronutrient problems, principally iron
and zinc, ar found in the Rio Grande Valley. How-
ever, current information shows that such problems
are confined to localized soil conditions and are not
general throughout the region.
More information about micronutrient fertiliza-
tion can be found in publications L-721, Zinc De-
ficiencies and Fertilization, and L-723, Identifying
and Correcting Iron Deficiency in Field Crops, (Texas
Agricultural Extension Service) available from your
county Extension office.
Conversion factors
Fertilizers containing phosphorus and potassium
are labeled as percent P205 and K20. Soil test values
are reported in these terms. However, plant analyses
results usually are reported as percentages of the
element. Th refore, the following factors are helpful
in converting from one form to the other:
From P20 5 to P multiply P205 by .44
From P to P20 5 multiply P by2.3
From ~O to K multiply K20 by .83
From K to K20 multiply K by 1.2
Concern about nutrient losses
The objective of fertilization is to apply nutrients
to deficient soils for better plant growth. Rate, method
and time of application should assure efficient use of
the nutrients, since economic losses result from im-
prop r fertilization.
utrients are lost or removed by (1) erosion or
movement of soil particles, (2) leaching of soluble
nutrients, (3) denitrification or volatilization of nitro-
gen and (4) crop removal. So follow good soil man-
ag ment and cultural practices to minimize erosion
losses. Also, nitrogen rates and time of application
should be compatible with the crop growth require-
ments of the crop and soil conditions.
Salinity and sodium
A substantial acreage in the Rio Grande Valley is
affected by soluble salts (salinity) or sodium, or pos-
sibly both where reclamation is planned or correctiv
measures intended.
Salt-affected (salinity or saline) soil is one that con-
tains enough water-soluble salts to affect plant growth.
Improvement generally requires elimination of the
salt source, and leaching and diluting the salt in the
root zone. Obtain soil salinity tests from the Extension
Soil and Water Testing Laboratory at Texas A&M
University. For sampling instructions, obtain a copy
Table 4. Application rates of P205 for grain sorghum at three
production levels
Soil
level 3000 Ib.lA. * 45001b.lA. 60001b.lA.
VL 30 40 60
L 20 30 50
M 0 20 40
H 0 0 0
VH 0 0 0
*Dryland or limited irrigation
Table 5. Application rates of P20 5 for corn at three production
levels
Soil
level 60 bu.lA. * 90 bu.lA. 120 bu.lA.
VL 40 60 80
L 20 40 60
M 0 20 40
H 0 0 20
VH 0 0 0
*Dryland or limited irrigation
Table 6. Fertilization of dryland Coastal, African Star and other bermuda grasses, Klein, Buffel and Bell Rhodes grass - three produc-
tion goal levels*
Tons of 8 to 10% Crude Protein Hay
Soil 4 6 8
level N P20 5 K20 ** N P20 5 K 2O** N P20 5 K 2O**
VL 100 40 200 60 300 80
L 80 20 160 40 260 60
M 0 0 120 20 200 40
H 0 0 0 0 120 0
VH 0 0 0 0 0 0
*Results from fertilizer demonstrations in the area show that when these grasses have no fertilization history they will yield 111:2 to 2 tons
per acre each year depending on rainfall.
**Not needed
ofform D-616, Information Sheetfor Salinity Analysis
ofSoil Samples (Texas Agricultural Extension Service),
from your county Ext nsion office.
Sodium-alE cted soil is high enough in sodium
to cause compaction, poor aeration and other un-
desirable physical conditions. Improvement requires
addition of calcium, usually as gypsum, and leaching
to r mov the sodium. In some calcareous soils,
sulfuric acid or elemental sulfur can be used to pro-
duce calcium sulfate by reacting with calcium car-
bonate. Under such conditions more improvement
time is required due to the rate of chemical reaction
in the soil.
Before investing in reclamation practices for either
salt-affected or sodium-affected soils, make a thorough
study of the problem and its causes.
Table 7. Fertilization of irrigated Coastal, African Star and other bermuda grasses, Klein, Buffel and Bell Rhodes grass - three produc-
tion goal levels*
Tons of 8 to 10% crude protei n hay
Soil 8 10 12
level N P20 S K2O** N P20 S K20** N P20 S K2O**
VL 300 80 400 100 500 120
L 260 60 340 80 420 100
M 200 40 280 60 340 80
H 0 0 0 40 0 60
VH 0 0 0 0 0 0
*Results from fertilizer demonstrations show that these grasses will produce 1Y2 to 2 tons per acre each year without fertilizer depending
on rainfall.
**Not needed
Table 8. Fertilization of small grains for grain and grazing
Small grains for Small grains for grazing
Soil grain only
only or grazing plus grain
level N P20 S K2O* N** P20 S K2O*
VL 60 40 60-120 50
L 40 30 60- 90 40
M 30 20 60 30
H 0 0 0 0
VH 0 0 0 0
*Not needed
**Use the higher rate of nitrogen under irrigated production.
Apply one-half of nitrogen at planting and the remainder in
early February.
Table 9. Fertilization of spring wheat for grain
Soil Mexican spring wheat for.grain
level N* P20 S K20**
VL 80-120 50
L 60-100 40
M 40- 80 30
H 0 0
VH 0 0
*Use the higher rate on fully irrigated wheat.
**Not needed
Table 10. Application rates of nutrients for forage sorghums and
sudan-sorghum - dryland and irrigated
Soil Dryland Irrigated
level N P20 S K20* N** P20 S K20*
VL 60 40 150 80
L 40 30 100 60
M 0 0 50 40
H 0 0 0 0
VH 0 0 0 0
*Not needed
**Should be divided into 40-50 pound applications with one ap-
plication preplant and an additional similar application after
each hay cutting, or grazed down and just ahead or irrigation
Table 11. Application rates of nutrients for sugarcane
Soil First year Ratoon crop
level* N** P20 S K20*** N** P20 S K2O***
VL 120 80 150 40
L 90 60 120 40
M 60 40 90 40
H 0 0 60 0
VH 0 0 0 0
*Prior to planting
**May need to split into two applications
***Not needed
Educational programs conducted by the Texas Agricultural Extension Service serve people of all ages regardless of socio-economic
level, race, color, sex, religion or national origin.
Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United States
Department of Agriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, 1914, as amended, and June 30, 1914.
2M-9-76 AGR 11-1


Field and Forage Crop Fertilization in the Lower Rio Grande Valley.

Texas A&amp;M Repository

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Field and Forage Crop Fertilization in the Lower Rio Grande Valley.

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Field and Forage Crop Fertilization in the Lower Rio Grande Valley.

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