Transcript SWES 316 Soil Fertility and Plant Nutrition

Trends in World Food Supply


Technology has decreased acreage
needed per person. With modern
agriculture, about 0.1 ha/person.
Number of people experiencing
famine has decreased since 1950.
Rapid increases in developing
world population mean that
greater per-acre yields will be
necessary.
10
E.S.E. Asia
S. Asia
9
Population/ha

S. America
8
N. America
7
Sub-sahara Africa
6
5
4
3
2
1
0
1960
1970
1980
Year
1990
2000
Trends in U.S. Agriculture
Cropland area has remained stable.
 Fewer farms and farmers, larger farms.
 Yield increases 1950 – 1992:






Corn
340%
Wheat
290%
Soybeans 170%
Alfalfa
170%
Why?

Improved technology (genetics, fertilizers, pest
control, irrigation)
Role of Nutrients/Fertilizers
Since 1960, fertilizer use in
the U.S. has increased:




N fertilizers by 400%
P fertilizers by 50%
K fertilizers by 150%
Estimates are that about
40% of yield increases
since 1930 are due to
increased fertilizer use.
Use of Fertilizers in U.S. and Canada
14
12
Million tons

10
N
P2O5
K2O
8
6
4
2
0
1954
1964
1974
1984
1994
2004
14000
12000
10000
13.3% of world N use
8000
6000
4000
2000
19
63
19
66
19
69
19
72
19
75
19
78
19
81
19
84
19
87
19
90
19
93
19
96
19
99
20
02
60
0
19
Nitrogen Fertilizer (10 3 short tons N/yr)
Trends in U.S. N Fertilizer Use
Data from The Fertilizer Institute (tfi.org)
Average Wheat and Rice yields in China, 221 BC - 1999
6,000
Yield, kg/ha
5,000
Wheat
Rice
4,000
3,000
2,000
1,000
C
20 -20
6B 1B
C C
-2
4
96 AD
01
13 27
68 9
-1
91
1
19
52
19
65
19
80
19
86
19
96
19
99
0
22
1B
Fertilizer use in China, 1950-1999
25,000
'000 t
20,000
15,000
10,000
N
P2O5
K2O
5,000
0
1950
PPIC, FAO 2002
1957
1964
1971
1978
1985
1992
1999
NPK consumption, kg/ha
300
250
200
World
Developing Countries
Developed Countries
China
India
150
100
50
0
1960
1970
1980
1990
2000
IFA, 2001
Key Soil Fertility Concepts
SWES 316
Section B
Outline for First Section Today
 Defining
soil fertility
 What makes soils fertile?
 Define growth curves
 Define response curves
 Evaluating outcomes of nutrient
management
 The “law of the minimum”
Definition of a Soil
A
natural occurring body, covering the earth
in a thin layer, synthesized in profile form,
from weathering and weathered rocks and
minerals, decomposed and decomposing
organic matter, and when properly supplied
with water and nutrients provides sustenance
for plant growth
Soil Fertility Defined

Brady: The quality of a soil that enables it to provide
essential chemical elements in quantities and
proportions for the growth of plants.

Anonymous: … an aspect of science concerned
with the sources and availability of essential
elements for plant growth with respect both to
quantity and quality of the crop produced.
What makes soils fertile?
 Lack
of weathering
 Parent material (mineralogy)
 High CEC
 Organic matter
 Adequate moisture
 Neutral pH
 Lack of excess salts
Soil Fertility
 Can
also be called:
Nutrient Management
Role of the Soil in Plant
Growth:
 Anchorage
 Storage/Supply
of Water
 Storage/Supply of O2
 Storage/Supply of Nutrients
Growth Curve
Plant Growth
Plant Response
Response Curve
Time
Amount of Input
Crop Growth Curve
The generalized crop growth
curve shown applies to annual
crops.
 Nutrient uptake follows the
same general pattern, but is
slightly earlier in time than
growth.
 Growth and nutrient uptake
in perennial crops is more
complicated.

Plant Growth
Growth Curve
Time
How can understanding
a crop growth curve
be useful?
-1
Total N Uptake (kg ha )
350
300
1993-94
1995-96
250
200
150
A
100
50
0
0
50
100
150
6
5
1993-94
1995-96
-1
-1
Daily N Flux (kg ha day )
Days After Planting
4
B
3
2
1
0
0
50
100
Days After Planting
150
Response Curves
Plant Growth
Response Curve
Amount of Input
Represents plant response to additions of any
rate-limiting input.
 Important points:




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
Decreasing slope
Diminishing returns
MC = MR
Upper limit = Genetic potential
Other factors can intervene
How can understanding
a crop response curve
be useful?
Crop Response
Model Response Curve
Maximum
Profit
Maximum
Yield
Amount of Input
Important Points on the
Yield (Response) Curve
 Maximum Yield

Determined by either genetic potential of the
crop or the presence of a limiting factor
 Maximum Profit


Point where marginal cost = marginal return
(MC=MR)
Depends on two things:
-
Cost of the input
Value of the crop
What's Happening here?
Plant Response
A
B
B: The input was needed
A: The input was not needed
C: Another factor limited
growth
C
Amount of Input
Nutrient Management
 Soil
Fertility is often concerned with the
problem of managing nutrients to be
applied to plants.
 Three general considerations:



Agronomic (how much is needed)
Economic (how can profit be maximized)
Environmental (minimize pollution)
Response Factors
 Crop Yield

The most important consideration in
nutrient management for most crops
 Crop

Quality
Maximum yield and optimum quality are
not always compatible. Example:
-
Malting barley yield vs. protein
Fruit Quality
Theory vs. Reality
 In
theory, any time we are practicing nutrient
management we should consider agronomic,
economic, and environmental ramifications.
 However, in reality some of these factors are
often ignored:


Economics of adding nutrients may be
unimportant in some high-value crops.
Environmental outcome is often ignored—
difficult to see or measure, who’s checking
anyway?
“Law of the Minimum”
 Crop
yield is limited by the most limiting
factor. When that factor is removed, yield is
limited by the 2nd most limiting factor, and so
on.
 Barrel metaphor
The Barrel
Liebig’s Law of the Minimum
Justus von Liebig – 1803-1873






He stated that the nutrient present in least relative amount
is the limiting nutrient.
soil contained enough N to produce 50 bu/ac
soil contained enough K to produce 70 bu/ac
soil contained enough P to produce 60 bu/ac
N would be the limiting nutrient
The crop uses up all of the deficient nutrient in the soil
making the yield directly proportional to the amount of the
deficient nutrient.