the problem of soil and land degradation p.c. wall cimmyt ®
TRANSCRIPT
The Problem of Soil and Land Degradation
P.C. Wall
CIMMYT®
Two major types of degradation:
• Soil erosion• Fertility decline
These are linked as erosion generally removes the most fertile soil, and the processes which lead to highly erodible soils are caused largely by soil fertility decline.
Effect of Tillage on Soil Erosion
Brazil (Sidiras)
Paraguay (Venialgo)
Conventional tillage 68.2 22.9Chisel plough 55
Soil Loss (t/ha/yr)
Zero tillage 6.9 0.5
Soil fertility degradation
What is a fertile soil?
A fertile soil allows the crop to produce close to the maximum dictated by the environment (moisture and radiation) … provided other
management factors are optimal.
Wheat Yield Over Time
Years of continuous agriculture
Yie
ld (
t/ha
)
0-0-0
120-60-0
Argentinian Pampa
Chemical Fertility
Biological Fertility
Physical Fertility
Biological Fertility
The Triangle of Soil Fertility
The forgotten parts of soil fertility
Profitable
Not Profitable
Years of Continuous Agriculture
Rel
ativ
e P
rofi
tab
ilit
y (%
)
100
0
Decline of Crop Yields and Profitability over Time using Conventional Agriculture
Cost of production
Problems Caused by Soil Physical Degradation
• Weak aggregates
• Lower soil porosity
• Soil crusting and surface sealing
• More soil compaction
Copied from Elwell, 1989
Chemical Fertility
Physical Fertility
Biological Fertility
S.O.M.
The Triangle of Soil Fertility
Soil Organic Matter (soil carbon) is linked to all aspects of soil fertility and Soil Quality
Place Soil Virgin or Pasture
Cultivated Years of cultivation
Itapúa, Paraguay Alfisol 4.5 1.5 Pampa, Argentina Argiudol 4.4 2.8 Paraná, Brasil Oxisol 5.0 2.0 Santa Cruz, Bolivia Inceptisol 3.1 1.4 2
Effect of Conventional Agriculture on
Soil Organic Matter (%)
Time
Raindrop effects (from Elwell, 1989)
Effect of Conventional Agriculture on
Water Infiltration Rates (mm/h)
Place Soil Virgin or Pasture
Cultivated Years of cultivation
Brasil (animal traction) Oxisol 136 31.3 7 Brasil Oxisol 136 0.2 20 Brasil (4 yrs. ZT) Oxisol 136 7.5 24
The surface crust impedes both water infiltration and gas interchange – especially oxygen.
And so this woman farmer knows she will get benefits from breaking the crust – but that involves a lot of work!
More rapid crop development
High Temperatures
Faster oxidation of organic matter
High intensity rainfall
Surface sealing
Surface crusting
Reduced plant populations
Reduction in Soil Structural Stability
Reduced water infiltration
Water stress
More crops per year
More tillage
Less root exploration
Soil compaction
Waterlogging
Soil erosion
High Temperatures
Faster oxidation of organic matter
High intensity rainfall
Surface sealing
Surface crusting
Reduced plant populations
Reduction in Soil Structural Stability
Reduced water infiltration
Water stress
More tillage
Less root exploration
Soil compaction
Waterlogging
Soil erosion
High Temperatures
Faster oxidation of organic matter
High intensity rainfall
Surface sealing
Surface crusting
Reduced plant populations
Reduction in Soil Structural Stability
Reduced water infiltration
Water stress
More tillage
Less root exploration
Soil compaction
Waterlogging
Soil erosionThe Vicious Circle
Chemical Fertility
Biological Fertility
Physical Fertility
Biological Fertility
The Triangle of Soil Fertility
Carbon lost as CO2 contributes to Global Warming
TILLAGE-INDUCED CO2 "FLUSH" AND CURRENT CROP RESIDUE
19 days after tillage
249
129.5
106.6 99.8
49.9
MP
MP+D
H2DH CP NT
TILLAGE TYPE
0
50
100
150
200
250
300
TO
TA
L C
LO
ST
IN 1
9 D
AY
S (
g C
/m )2
185 g C/m from residueof previous wheat crop
2
1079.2
2686.1
0
500
1000
1500
2000
2500
3000
3500
NT MP
Cu
mu
lati
ve C
O2 F
lux
( g
CO
2 m
-2)
Long Term Study July 14 - October 9, 1998Cumulative loss after 87 days (avg of 4 reps)
" A nation that destroys its soil destroys itself."
-- Franklin D. Roosevelt, 1937
