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.

0

1

2

3

4

5

6

7

8

9

10

1960 1970 1980 1990 2000

Year

Po

pu

lati

on

/ha

 E.S.E. Asia

 S. Asia

 S. America

 N. America

Sub-sahara Africa

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

0

2

4

6

8

10

12

14

1954 1964 1974 1984 1994 2004

Mil

lio

n t

on

s

N

P2O5

K2O

Trends in U.S. N Fertilizer Use

0

2000

4000

6000

8000

10000

12000

14000

1960

1963

1966

1969

1972

1975

1978

1981

1984

1987

1990

1993

1996

1999

2002

Nitro

gen

Fert

ilize

r (1

03 sho

rt to

ns N

/yr)

Data from The Fertilizer Institute (tfi.org)

13.3% of world N use

Average Wheat and Rice yields in China, 221 BC - 1999

Fertilizer use in China, 1950-1999

0

5,000

10,000

15,000

20,000

25,000

1950 1957 1964 1971 1978 1985 1992 1999

'000

t

N

P2O5

K2O

0

1,000

2,000

3,000

4,000

5,000

6,000

Yie

ld, kg

/ha

Wheat

Rice

PPIC, FAO 2002

0

50

100

150

200

250

300

1960 1970 1980 1990 2000

WorldDeveloping CountriesDeveloped CountriesChinaIndia

NPK consumption, kg/ha

IFA, 2001

Key Soil Fertility Concepts

SWES 316Section 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

Time Amount of Input

Plan

t Gro

wth

Growth Curve Response Curve

Plan

t Res

pons

e

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.

Time

Plan

t Gro

wth

Growth Curve

How can understandinga crop growth curvebe useful?

BR

OC

CO

LIA

B

0

1

2

3

4

5

6

0 50 100 150

Days After Planting

Dai

ly N

Flu

x (k

g ha

-1 d

ay-1)

1993-94

1995-96

0

50

100

150

200

250

300

350

0 50 100 150

Days After Planting

To

tal

N U

pta

ke (

kg

ha-1

)

1993-94

1995-96

Response Curves

Represents plant response to additions of any rate-limiting input.

Important points: Decreasing slope Diminishing returns MC = MR Upper limit =

Other factors can intervene

Genetic potential

Amount of Input

Response Curve

Plan

t Gro

wth

How can understandinga crop response curvebe useful?

Model Response Curve

Amount of Input

Cro

p R

espo

nse

Maximum Profit

MaximumYield

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

Plan

t Res

pons

e

Amount of Input

A

B

C

What's Happening here?

B: The input was neededA: The input was not needed

C: Another factor limitedgrowth

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.