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Forage sorghum growth and nutrition as affected by soil variability

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Title:
Forage sorghum growth and nutrition as affected by soil variability
Creator:
Lilly, Donald Paul, 1962-
Gallaher, Raymond N
University of Florida -- Agronomy Dept
Place of Publication:
[Gainesville Fla
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Agronomy Department, IFAS, University of Florida
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English
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7, [11] leaves : ; 28 cm.

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Sorghum -- Field experiments -- Florida ( lcsh )
Soil fertility -- Florida ( lcsh )
Forage plants -- Florida ( lcsh )
City of Gainesville ( flgeo )
Nutrients ( jstor )
Forage ( jstor )
Soils ( jstor )
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bibliography ( marcgt )

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Bibliography:
Includes bibliographical references (leaves 6-7).
General Note:
Chiefly tables.
General Note:
Agronomy research report - University of Florida Agronomy Department ; AY 89-09
Statement of Responsibility:
D.P. Lilly and R.N. Gallaher.

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University of Florida
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62574444 ( OCLC )

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Agronomy Research Report
AY-89-09



Forage Sorghum Growth and Nutrition
As Affected by Soil Variability



D.P. Lilly and R.N. Gallaher
Graduate student and professor, Agronomy Dept.,
IFAS, Univ. of Florida, Gainesville, FL 32611










Agronomy Research Report AY-89-09


Forage Sorghum Growth and Nutrition
as Affected by Soil Variablilty

D.P. Lilly and R.N. Gallaher
Graduate student and professor, Agronomy Dept.,
IFAS, Univ. of Florida, Gainesville, FL 32611


Abstract

A field experiment with forage sorghum (Sorghum bicolor L.
Moench) cultivar 'FS 25-A' was conducted on an area dominated by
Arenic and Grossarenic Paleudults where a clay gall was present.
Soil and plant samples were taken 41 days after planting to
determine and illustrate the effect of soil texture variability
and residual soil fertility on the growth and mineral nutrition
of forage sorghum. Five treatments with three replications were
designated as 0.25, 0.50, 0.75, 1.00, and 1.25 m plant heights in
a randomized complete block design. Soil samples were analyzed
for texture, pH, organic matter (OM), N, P, K, Ca, Mg, Cu, Fe,
Mn, Zn, and Al. Plant samples were analyzed for dry matter, N,
P, K, Ca, Mg, Cu, Fe, Mn, and Zn concentrations. Soil samples
increased in clay, OM, and extractable nutrients from the 0.25 to
the 1.25 m plant height treatments. Plant samples increased in N
and K concentration but decreased in Ca and most micronutrients
as plant height increased from 0.25 to 1.25 cm. These data show
the strong influence of soil variability on growth and nutrient
relationships in forage sorghum.


Key Words

Percent clay, soil texture, N, P, K, Ca, Mg, micronutrients, clay
gall.


Introduction

Agronomists have long known that there is a relationship
between the texture and fertility of a soil, and that the
fertility of a soil affects the growth and nutrition of the crop
grown on that soil. They have worked to predict the optimum
amount of fertilizer for the optimum yield of a crop. They have
also worked to establish the critical nutrition levels of the
plant requiring elements needed to obtain optimum yield. Lockman
(1972) has established nutrient sufficiency levels for grain
sorghum (Sorghum bicolor L. Moench) which are useful in
monitoring the nutrition status of the crop at different stages.
The objective of this experiment was to observe the growth and
nutrition of forage sorghum during the late vegetative stage in a


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sandy field plot which had varying residual soil fertility and
varying soil texture due to the presence of a clay gall.


Materials and Methods

A field experiment was conducted at the Green Acres Agronomy
Farm located 12 miles west of Gainesville, Florida on an area
dominated by Arenic and Grossarenic Paleudults (loamy, silicious,
hyperthermic) (Soil Survey Staff, 1984) where a clay gall was
present. Forage sorghum cultivar 'FS 25-A' was planted on 11
August 1988 at the rate of 28 kg seed ha-I in a no-tillage
system. Glyphosate [N-(phosphonomethyl) glycine] was applied 10
days before planting at the rate of 4.68 L ha-1. No fertilizer
was applied to the crop. The previous crop was wheat (Triticum
aestivum L.) and crimson clover (Trifolium incarnatum L.)
intercropped in a conventional tillage system.

Sorghum plants were sampled 41 days after planting (DAP) in
a randomized complete block design with three replications and
five treatments. The five treatments consisted of sorghum plants
at heights 0.25, 0.50, 0.75, 1.00, and 1.25 m and the soil
adjacent to the plants. For each treatment and replication, the
youngest mature leaf (yml) was removed from 10 plants in each
square meter and then the above ground portion of all the plants
in one square meter was removed.

Plant samples were washed with water to remove soil from the
field and then dried in a forced air oven at 70 C. Dry whole
plant samples were weighed to the nearest g and dry yml samples
were weighed to the nearest hundredth of a g. Whole plant
samples were chopped in a hammermill and a representative sample
was removed and ground in a Wiley mill with a 2 mm stainless
steel screen. Youngest mature leaf samples were ground
similarly. Ground plant samples were stored in air tight
plastic bags.

Both whole plant samples and yml samples were dried for at
least four hours at 70 C prior to mineral and N analysis. For
mineral analysis, 1.0 g samples were weighed, placed in pyrex
beakers, and then dry-ashed at 480 C for a minimum of 6 hours. A
small amount of deionized water and 2 mm of concentrated HC1 were
added to the ash and this mixture was boiled until dry. This
procedure was repeated a second time except that ash solutions
were removed and allowed to cool when they began to boil. The
ash solutions were diluted to 100 ml and stored in a plastic vial
prior to analysis. Plant P was analyzed by colorimetry,
plant K was analyzed by atomic emission spectrophotometry and
plant Ca, Mg, Cu, Fe, Mn, and Zn were analyzed by atomic
absorption spectrophotometry.










For N analysis, between 0.1000 and 0.2000 g samples were
weighed and placed into a 75 mm pyrex test tube along with 3.4 g
of a prepared catalyst (90% anhydrous K2S04 and 10% anhydrous
CuS04), 10 mm concentrated H2S04, and two or three boiling chips.
The test tube contents were mixed and 2 mm of 30% H202 was added
in 1 mm increments. Small funnels were placed into the top of
the test tubes to allow refluxing during digestion. Samples were
digested on an aluminum block digester (Gallaher et al., 1975) at
385 C for 4 hours. After cooling, samples were simultaneously
mixed and diluted with deionized water and then brought to 75 ml
volume with deionized water and stored in plastic vials. Plant N
was analyzed on the Technicon Autoanalyzer II System.

Soil samples were collected from the top 15 cm of the soil
profile within the one square meter area where the plant samples
were collected. Soil samples were air dried, ground, and sieved
to pass through a 2 mm stainless steel screen. Soil pH was
measured with a glass electrode using a 2:1 water to soil ratio.
Percent clay in the soil was determined by mechanical analysis
using a soil hydrometer (Bouyoucus, 1936 and Day, 1965). Percent
organic matter in the soil was determined using the Walkley-Black
method (Walkley, 1935). Four g of each soil sample were used for
analysis of P, K, Ca, Mg, Fe, Cu, Mn, Zn, and Al using the
Mehlich I double-acid extraction method (Mehlich, 1953). Soil P
was analyzed by colorimetry, soil K was analyzed by atomic
emmision spectrophotometry, and soil Ca, Mg, Fe, Cu, Mn, Zn, and
Al were analyzed by atomic absorption spectrophotometry. Two g
of each soil sample were used for N analysis using the modified
Kjeldahl N analysis procedure discussed under plant N.

Whole plant nutrient contents were derived by adding
nutrient contents for the whole plant and yml together. Nutrient
concentrations were multiplied by the dry matter weights of the
whole plant and yml to obtain contents. Analysis of variance and
means separation as determined by LSD were obtained using MSTAT
on the Tandy 1000 microcomputer.


Results and Discussion

The field plot had sorghum plants which varied in appearance
from pale green to dark green as the level of clay present in the
soil and the soil fertility increased. Table 1 shows the means
of the soil pH, percent clay, and percent organic matter for the
corresponding plant height treatment. Soil pH did not vary much
between plant height treatments. Percent clay in the soil
increased from 5.6% to 15.6% as the soil texture changed from
sands to sandy loams. Percent organic matter in the soil also
increased significantly among the five plant height treatments.










The highest values for nutrient concentrations in the soil
were always found at the 1.25 m plant height treatment (see
Tables 2 and 3). Soil N concentration increased from the 0.25 to
the 1.00 plant height treatment before leveling off. Both soil P
and Ca concentrations increased gradually before increasing
significantly at the 1.25 m plant height treatment. Soil K
concentration increased only slightly and soil Mg increased
gradually from the 0.25 to 1.25 m treatment. No significant
increase in soil Cu concentration was present in the five
treatments and little significant increase was present in soil Zn
concentration. Soil Fe concentration increased in all treatments
but the increase leveled off in the 1.25 m treatment. Soil Mg
and Al increased in each treatment although not all increases
were significant.

Whole plant dry matter increased from the 0.25 to the 1.00
plant height treatment before leveling off (see Table 4). Dry
matter for the yml increased with each successive treatment.

The yml nutrient concentrations of the five plant height
treatments are given in Tables 5 and 6. Leaf (yml) N
concentration increased gradually from the 0.25 to the 1.25 m
plant height treatment. Leaf P concentration did not increase
significantly throughout all five treatments and leaf K and leaf
Mg concentrations flucuated without a very significant increase
among the five treatments. Leaf Ca concentration decreased
significantly in the 0.25, 0.50, and 0.75 m treatments before
leveling off. Leaf Fe and Zn concentrations decreased from the
0.25 to the 1.00 m treatments before increasing in the 1.25 m
treatment. Leaf Cu concentration decreased from the 0.25 to the
1.25 m treatment and leaf Mn concentration decreased in the 0.25
to 0.75 m treatments before increasing last two treatments.

There was very little significant difference in the whole
plant nutrient concentrations throughout the five treatments
(see Tables 7 and 8). This is due to a dilution effect which
resulted in very little increase in nutrient concentrations or
resulted in a decrease in nutrient concentrations. Plant (whole
plant) N, Ca, Mg, and Fe concentrations did not increase or
decrease significantly in the five plant height treatments.
Plant P concentration decreased from the 0.25 to the 0.75 m
treatments before increasing slightly. Plant K concentration
flucuated in the 0.25 to the 1.00 m treatments before increasing
at the last treatment. Plant Cu decreased from the 0.25 to 0.75
m treatment before leveling off and plant Zn concentration
decreased from the 0.25 and 0.50 m treatments to the 0.75 to 1.25
m treatments. Plant Mn concentration flucuated in the first four
treatments before increasing to the highest concentration at the
1.25 m treatment.










Lockman (1972) established critical nutrient levels in
sorghum for the third leaf during the vegetative stage and for
the whole plant at approximately 23 to 39 days after planting
(DAP). Comparisons of nutrient concentrations in the yml and
whole plant were made with Lockman's critical nutrient levels in
sorghum. Leaf (yml) N and K concentrations were low at all
treatments but approached sufficiency levels at the 1.25 m plant
height treatment. Leaf P, Ca, and Mg concentrations were
sufficient at all five plant height treatments as were leaf Cu,
Fe, and Mn concentrations; however, leaf Cu concentrations were
just barely above sufficiency levels (Lockman, 1972). Leaf Mg
concentrations were also sufficient according to sufficiency
levels found by Gallaher et al. (1975) of the fourth leaf at late
pollination stage. Leaf Mn concentrations were adequate by
critical Mn nutrient levels found by Ohki (1975). Leaf Zn
concentrations were below sufficiency levels for all treatments
but the 0.25 m plant height treatment was close to sufficiency
levels (Lockman, 1972).

Plant (whole plant) N, K, and Ca concentrations were below
sufficiency levels at all treatments but plant P and Mg were
above sufficiency levels as provided by Lockman (1972). All
plant micronutrient (Cu, Fe, Mn, and Zn) were below sufficiency
levels of the critical nutrient levels by Lockman (1972).

Plant (whole plant) N content, as shown in Table 9,
increased from the 0.25 to the 1.00 m plant height treatment
before leveling off as did plant P, Ca, and Mg contents. Plant
Cu, Fe, Zn, and Mn content (Table 10) increased in the 0.25 to
1.00 m plant height treatments before leveling off in the 1.25 m
treatment. Plant K content significantly increased at each
successive plant height treatment from .25 to 1.25 m. Pal et al
(1982) published the whole plant content of grain sorghum
cultivar 'CSH-1' grown with supplied N and P fertilizers (120 kg
N ha-i and 26 kg P ha-1) during the entire growing season. If
comparisons are made with 'CSH-1' at 42 DAP, N, P, and K contents
were adequate or above adequate at the 1.00 and 1.25 m plant
height treatments.


Conclusion

There were high correlations between the amount of clay
present in the soil and the soil test extractable nutrients,
plant dry matter, nutrient concentration of the yml, and nutrient
content of the whole plant. The sandy areas of the plot were low
in residual fertility and contained a less measurable amount of
soil nutrients. This resulted in short, stunted forage sorghum
plants which were visibly deficient in plant nutrients. This can
be compared to the areas of the plot where the clay gall was
present. Plants were between 2 to 4 times taller and showed few
if any deficiency symptoms. Residual fertility of the soil in










these areas was much higher.


The 1.00 and 1.25 m plant height treatments were growing in
soil which supplied or almost supplied the nutrients needed for a
productive forage sorghum crop. Generally speaking, N, P, and K
were adequately supplied by the soil although P levels were much
higher than required and N aqd K soil levels could have been
higher. All other nutrients were supplied adequately as well
with the exception of Zn and possibly Cu.

The best diagnostic plant samples in this experiment were
the yml samples. These plant samples more accurately revealed
the current nutrition of the sorghum whereas whole plant nutrient
concentrations provided misleading values due to the dilution of
the nutrient concentrations in the plant. Whole plant contents
derived from dry matter weights and yml and whole plant nutrient
concentrations provided a clear picture of which plants were
growing in more fertile soil and with adequate rates of
fertility. Correlations between whole plant contents and plant
dry matter were all high. (Correlation coefficients of whole
plant contents and whole plant dry matter are found in Table 11.)

This experiment points out the importance of considering all
the variables involved in field plot research. Results from
research can be confounded by varibles which are overlooked or
not observed closely enough. In this case, the failure of a
researcher to observe the significant change in texture, OM, and
fertility status of the soils in this field plot would confound
his results.


Literature Cited

Bouyoucus, G.J. 1936. Directions for making mechanical analysis
of soil by hydrometer method. Soil Sci. 42(3).
Day, P.R. 1965. Particle fractionization and particle size
analysis. In C.A. Black (ed) Methods of soil analysis, part I.
Soil Sci. Soc. Amer., Madison, Wis. pp. 545-567.
Gallaher, R.N., H.B. Harris, O.E. Anderson, and J.W. Dobson, Jr.
1975. Hybrid grain sorghum response to magnesium fertilization.
Agron. J. 67:297-300.
Gallaher, R.N., C.O. Weldon, and J.G. Futral. 1975. An aluminum
block digester for plant and soil analysis. Soil Sci. Soc
Amer. Proc. 39:803-806.
Lockman, R.B. 1972. Mineral composition of grain sorghum plant
samples. Part III: Suggested nutrient sufficiency limits at
various stages of growth. Comm. Soil Sci. Plant Anal. 3:395-
403.
Mehlich, A. 1953. Determination of P, Ca, Mg, K, Na, and NH4+.
North Carolina Soil Test Divison (mimeo). North Carolina State
University, Raleigh, North Carolina.










Ohki, K. 1975. Manganese supply, growth, and micronutrient
concentration in grain sorghum. Agron. J. 66:5-10.
Pal, U.R., U.C. Upadhyay, S.P. Singh, and N.K. Umrani. 1982.
Mineral nutrition and fertilizer response of grain sorghum in
India-a review over the last 25 years. Fert. Res. 3:141-159.
Soil Survey Staff. 1984. Official series description of the
Arredondo series. United States Government Printing Office,
Washington, D.C.
Walkley, A. 1935. An examination of methods for determining
organic carbon and nitrogen in soils. J. Agron. Soc. 25: 598.



















Table 1. Soil analysis: Electroded pH,
percent clay, and potassium
dichromate organic matter.

Plant
Height pH CLAY OM
m ---%-- ---

0.25 6.00 a 5.8 b 1.35 d
0.50 6.07 a 7.1 b 1.57 cd
0.75 6.00 a 7.8 b 1.66 bc
1.00 5.87 a 11.5 ab 1.92 ab
1.25 5.83 a 15.6 a 2.12 a

LSD.05 0.27 6.4 0.30

Means in columns not followed by the
same letter are significantly different at
the .05 level of probability as determined
by LSD.




















Table 2. Soil analysis: Kjeldahl N and Mehlich I extractable P, K,
and Mg.

Plant
Height N P K Ca Mg
m ------------------mg/kg-------------------

0.25 449 c 53 c 23 b 325 c 33 c
0.50 562 bc 118 bc 39a 587 bc 66 bc
0.75 610 b 167 bc 34ab 680 bc 72 bc
1.00 762 a 234 b 37a 876 b 99 ab
1.25 871a 452a 43a 1513a 130a

LSD.05 118 175 13 485 47

Means in columns not followed by the same letter are significantly
different at the .05 level of probability as determined by LSD.




















Table 3. Soil Analysis: Mehlich I extractable Cu, Fe, Mn, Zn,
and Al.

Plant
Height Cu Fe Mn Zn Al
m ----------------mg/kg------------------

0.25 0.08 a 8.9 c 2.43 c 0.84 b 263 c
0.50 0.08 a 11.8 c 3.04 bc 1.31 ab 340 b
0.75 0.13 a 16.6 b 4.05 b 2.23 ab 366 b
1.00 0.12 a 22.1 a 3.95 b 1.88ab 379 b
1.25 0.31 a 22.8 a 5.99 a 2.77 a 473 a

LSD.05 0.29 3.0 1.30 1.71 75

Means in columns not followed by the same letter are significant-
ly different at the .05 level of probability as determined by LSD.


jr~________l_________CY__r

















Table 4. Whole plant and youngest
mature leaf dry matter of
forage sorghum.


Plant
Heiaht


Whole
Plant


Youngest
Mature
Leaf


- m g/m2 g*

0.25 24 d 0.65 d
0.50 81 c 2.92 c
0.75 145 b 6.89 b
1.00 236 a 7.32 b
1.25 226 a 9.82 a

LSD.05 44 1.81

* composed of 10 plants

Means in columns not followed by the
same letter are significantly different
at the .05 level of probability as
determined by LSD.



















Table 5. Plant analysis: Youngest mature leaf N,
Mg concentrations of forage sorghum.


P, K, Ca, and


Plant
Height N P K Ca Mg
- m -----------------g/kg------------------

0.25 22.6 c 4.33 a 13.2 b 8.03 a 3.80 a
0.50 24.8 bc 4.97 a 15.6 ab 5.13 b 3.33 ab
0.75 27.7 ab 4.10 a 13.4 b 3.70 c 2.60 b
1.00 28.1 a 4.13 a 14.2 b 3.63 c 2.87 b
1.25 30.3 a 4.83 a 18.1 a 3.33 c 3.00 ab

LSD.05 3.1 0.98 3.4 1.26 0.88

Means in columns not followed by the same letter are significant-
different at the .05 level of probability as determined by LSD.



















Table 6. Plant analysis: Youngest mature leaf Cu, Fe,
Mn, and Zn concentrations of forage sorghum.

Plant
Height Cu Fe Mn Zn
m--------------mg/kg---------------

0.25 5.00 a 101 a 21.7 ab 19.0 a
0.50 3.67 b 86 ab 15.3 c 16.0 ab
0.75 2.67 bc 71 b 16.7 bc 14.3ab
1.00 2.67 bc 70 b 21.0ab 11.3 b
1.25 2.00 c 84ab 24.0a 11.7 b

LSD.05 1.03 19 5.3 6.6

Means in columns not followed by the same letter are
significantly different at the .05 level of probability
as determined by LSD.



















Table 7. Plant analysis: Whole plant N, P, K, Ca, and Mg
concentrations of forage sorghum.

Plant
Height N P K Ca Mg
m ----------------g/kg-----------------

0.25 19.0 a 4.47 a 15.5 b 4.43 a 3.33 a
0.50 19.1 a 4.10 ab 17.8 b 4.17 a 3.43 a
0.75 20.5 a 3.47 b 18.8 b 3.97 a 3.37 a
1.00 20.6 a 3.50 b 17.3 b 3.93 a 3.57 a
1.25 20.9 a 3.77 ab 23.9 a 3.63 a 3.40 a

LSD.05 3.9 0.78 3.4 1.12 0.53

Means in columns not followed by the same letter are signifi-
cantly different at the .05 level of probability as determined
by LSD.



















Table 8. Plant analysis: Whole plant Cu, Fe, Mn,
and Zn concentrations of forage sorghum.

Plant
Height Cu Fe Mn Zn
m ------------mg/kg-------------

0.25 3.67 a 74 a 26.3 ab 21.3 a
0.50 2.67 b 71 a 21.3 b 21.3 a
0.75 2.00 c 72a 22.7 b 14.3 b
1.00 1.67 c 71 a 28.3 a 14.0 b
1.25 2.00 c 74a 31.0a 12.0 b

LSD.05 0.60 12 5.2 3.8

Means in columns not followed by the same letter
are significantly different at the .05 level of prob-
ability as determined by LSD.




















Table 9. Whole plant N, P, K, Ca, and Mg contents of forage sorghum.

Plant
Height N P K Ca Mg
- m ------------------g/m2---------------------

0.25 0.49 c 0.11 d 0.38 e 0.12 d 0.09 c
0.50 1.59 c 0.35 c 1.48 d 0.36 cd 0.29 bc
0.75 3.16 b 0.53 b 2.83 c 0.60 bc 0.51 b
1.00 5.10 a 0.85 a 4.13 b 0.97 a 0.87 a
1.25 5.06 a 0.90 a 5.74 a 0.86 ab 0.80 a

LSD.05 1.35 0.12 0.76 0.32 0.23

Means in columns not followed by the same letter are significantly
different at the .05 level of probability as determined by LSD.



















Table 10. Whole plant Cu, Fe, Mn, and Zn contents of
forage sorghum.

Plant
Height Cu Fe Mn Zn
m -------------g/m2----------------

0.25 0.09 c 1.9 c 0.66 c 0.54 d
0.50 0.23 bc 6.0 c 1.79 c 1.80 c
0.75 0.31 ab 11.0 b 3.36 b 2.18 bc
1.00 0.42 a 17.3 a 6.79 a 3.34 a
1.25 0.47 a 17.8 a 7.22 a 2.80 ab

LSD.05 0.17 4.3 1.39 0.63

Means in columns not followed by the same letter are
significantly different at the .05 level of probability
as determined by LSD.


















Table 11. Correlation coefficients of whole plant contents and plant dry matter.

N P K Ca Mg Cu Fe Mn Zn
N 1.000
P 0.978 1.000
K 0.940 0.967 1.000
Ca 0.983 0.944 0.876 1.000
Mg 0.991 0.975 0.915 0.988 1.000
Cu 0.938 0.914 0.877 0.956 0.946 1.000
Fe 0.987 0.987 0.962 0.956 0.979 0.915 1.000
Mn 0.965 0.979 0.960 0.927 0.954 0.878 0.977 1.000
Zn 0.927 0.940 0.855 0.938 0.940 0.895 0.932 0.907 1.000
DM 0.995 0.988 0.942 0.978 0.992 0.932 0.990 0.972 0.952