The document addresses the connection between soil science, water management, and agricultural productivity amid climate change challenges and a growing population. It highlights the urgent need to enhance water use efficiency and reduce environmental impacts while advocating for innovative soil research and sustainable practices. Key considerations include the limited availability of suitable agricultural land, the impacts of climate variability on crop yields, and the necessity for improved monitoring of soil and water management practices.

1. SIAGRO 2014
Sao Carlos, Brazil
November 20-22, 2014
What Soil Science can Offer, for a Society
Demanding more Food with less Water
and Energy, Reducing Environmental
Impacts, while our Climate is Changing ?
Jan W Hopmans

2. What will be covered ?
• Nexus of Soil & Water Science in Society
- Food – Water – Land – Energy - Climate
• Opportunities for Soil Science
- Irrigation Water Management
- Root/Soil Interactions
- Nitrogen Management in Irrigated Soils
• Research Challenges

3. - for both agriculture
& natural ecosystems,
- and mediates most
of the life-sustaining
interactions among
land, surface water
and the atmosphere
Soil & Human Health
ADVOCATE
Soils Sustain Life:

4. SOILS are integral to
FOOD-WATER-ENERGY NEXUS
of global society, but varies regionally
Food
LAND USE &
CLIMATE CHANGE
Energy Water
Climate change will affect these
inter-relationships, while suitable land
available for agriculture is becoming limited

5. FACTS: Water for food Water for life
A comprehensive Assessment of Water Management and Agriculture
(David Molden, Ed. IWMI, 2007)
 Is there enough water to produce food for a growing
population over the next 40 years?
 It takes about 1L of water per calorie of food (daily dietary
needs is about 2-3 m3/day, or 600-800 gallons/day;
 Global agricultural crop production takes about 70% of
developed freshwater, of which about 30% is groundwater;
 Whereas currently about 15% of agriculture is irrigated, it
produces about 45 % of global food production;
 About 1/3 of irrigated land is salt-affected;

6. PEAK SOIL (data from World Resources Institute)
Annual expansion rate of new farm
land is about 0.27 % / year;
Over the past 40 years, about 2
billion ha of soil (15% earths land
surface and 30% of the world’s
cropland) has been degraded and
has become unproductive.
Between 1982-2007, close to 10 Mha of
US ag land has been converted for
development (1 ha/2 minutes), USDA
As more marginal land is turning into agricultural
production, worlds agricultural acreage is running out

7. The Global Challenge
(Wada and Bierkens, 2014)
(Burney et al, PNAS, 2010)
In past 50 years, population more than
doubled, irrigated area doubled, and water
withdrawals increased by about 250%.

8. Global Food Production Challenges
From 1950-2000, global population doubled, while per capita
food production increased by 25 % (green revolution).
Future population growth will require about doubling of food
production in the coming 50 years, and must use less water
per unit of output produced, otherwise it will require double
the water requirements of today.
In part, because of dietary changes,
and shift away from cereals
towards live-stock/fish,
and high-value crops

9. Historical Crop Production Trends
Grassini, Eskridge and Cassman (Nature communcations, 2013)
•Incredible achievement
•Evidence of plateaus in world’s
most intensive cropping systems
(biophysical/photosynthetic
yield ceiling);
• Yield stagnation at low-yield
levels (lack of agricultural inputs,
infrastructure, & capital)
• These regions have highest
potential for yield intensification
(no need for cropland expansion)

10. Rethinking Agriculture
• Current trends indicate that population growth is
outpacing food production in many parts of the
world, and in 64 of 105 developing countries;
Total Population of the Continents
• Based on a 2500 cal/day diet water demand under
business as usual will increase to approximately
13,000 km3 by 2050 (double of that of 2000 year)

11. Where might the water come from?
Blue Water
• Increase water use efficiency of irrigated
agricultural systems – but salinity impacts
• Increased use of more marginal quality water
• Expand land area for irrigated agriculture:

12. Global Water Scarcity – Imbalance between
fresh water demand and availability
Water scarcity is a
major threat to
agriculture and
food security in
developing
countries .
(1/5 of world population
faces physical water
scarcity and 1/4 suffers
from economic water
scarcity).
When annual water supplies drop below 1,000 m3 per person,
the population faces water scarcity (3,000 L/day);

13. Food for Thought Green Water
• Rainfed agriculture occupies about 85% cropland, yet irrigation
provides 46% of the gross value of world’s agricultural production.
Green water: ~65%
• Increase of land & water productivity of rain-fed agricultural
systems will be critical, producing more food per unit water (e.g.
crop genetics)

14. A Bigger Rice Bowl
(Economist, May 2014)
• Demand for rice is rising in Asia and Africa
• Rule of thumb: every additional 1 billion of people requires 100 million
ton of rice; Yet, rice yields are stabilizing/falling
• Rice is among the largest water users in agriculture –
• Now requires yield boosting for rainfed rice (drought and flood
resistant varieties)

15. Water Productivity
Unbelievably low, for yields < 3 t/ha for cereal crops
(essential all in developing countries)
Evaporation losses
Significant water
savings can be
gained
Increase T/ET ratio
Relationship between water productivity and yield for cereal crops in
tropical/temperate farming systems (Rockstrom et al., PNAS, 2007)

16. Impacts of Limited Water Supply for Crop
Production can be partly mitigated using
Technological Solutions . . . .
• Agricultural Biotechnology (plant breeding & molecular
genetics) – improved drought & salinity tolerance
• Water Resources Engineering (water transfers?)
• Irrigation Technologies and Improved Irrigation Scheduling
• Fresh water Generation (e.g. ,reverse osmosis)
• Improved soil, water management, and agronomic practices,
including improved water use efficiency and conservation

17. FUTURE AGRICULTURE MUST BECOME
BOTH MORE PRODUCTIVE AND SUSTAINABLE
Requires better understanding of how plants take up water and nutrients, so we can do more with less;
Need to improve water use efficiencies, and nitrate
use efficiencies
Requires Innovative Soil Research,
in combination with plant science and engineering technologies

18. Conservation Tillage
Central Valley, CA
No-till cotton and tomatoes
Reduced till & Direct Seeding
Reduces Energy Footprint
CASI, Jeff Mitchell , UC CE Specialist

19. Thermal Neutron
Non-invasive Neutron Tomography
CT - MNRC
Nuclear Research Reactor
Gadolinium control rods
•Neutron beam

20. Plant’s Response to Differential Soil Water Content
( Moradi, Oswald, Menon, Carminati, Lehmann & Hopmans,
Special Publication, SSSA)
Moradi et al. 2012, New Phytologist

21. Climate – Water – Food Nexus
Food
Climate Water
Increasing atmospheric CO2 causes increasing earth surface
temperatures, affecting food production and water availability

22. Climate Trends and Global Crop Production Since 1980
(Lobell et all., 2011, Science)
Estimated net impact of climate trends for 1980-2008
on crop yields by country, divided by the overall yield
trend per year for the same period.
Temperature trends
Precipitation trends
Maps of 1980-2008 linear trends in
temperature (A) and precipitation (B)
For the growing season of the
Predominant crops (maize, wheat, rice,
and soybean).
Yield Trends largely Determined by Temperature
rather than Precipitation Trends

23. Climate change Brazil
Climate Change and extreme events in Brazil (FBDS, 2012 – H. Silveira Pinto)
• Longer dry spells in eastern Amazon;
• Reduction in precipitation;
• Increase in frequency of daily and seasonal extremes of
temperature and rainfall;
Impacts:
• Hydropower generation
• Agricultural economy is
expected to by most
vulnerable to climate change
(30% of Gross Domestic Product)

24. Agricultural impacts of climate
change in Brazil
• If predicted temperature increases for 2050 would
happen today, all main crops (soybeans, rice, corn,
beans, cassava, sunflower, cotton, coffee) would lose
around 15% of their production areas.
• Only sugar cane would
increase its potential
area for cultivation.
• Longer drought periods
can be partly compensated
for by supplemental irrigation

25. CALIFORNIA
• Largely (semi) arid climate
• 12th largest economy in the world
• Grows 50% fruits and vegetables and is
number 1 dairy state in the US
• ~25 million acres agricultural lands (10 million ha)
• 52% is pasture/rangeland and 37% is irrigated crop
land (10 million acres or 4 million ha)
• Irrigated agriculture requires about 27 MAF (27 BCM) of
developed water (surface plus groundwater)
• State with most endangered ecological communities in the US
• Significant climate warming is forecasted, which will negatively
impact available water supplies and mandate change/regulate
state-wide water management practices/policies.

26. Climate Change Impacts on CA Water
Resources
• More rain than snow
• Earlier snow melt
• Higher probability of flooding
• Less reliable water supply from reservoirs
in the Valley for irrigation

27. California Drought 2011-14
• About 1 million acres
is expected to be
fallowed;
• 2013-14 water year
Is driest year on record
• Precipitation is about
1/3 of normal year
The Palmer Drought Severity Index was devised in 1965, to assess moisture
status comprehensively. It uses temperature and precipitation data to
calculate water supply and demand, incorporates soil moisture.

28. Continued expansion of tree crops/vines in CA
As water becomes less available

29. California groundwater depletion and nitrate concentration
Groundwater pumping increased from about 1/3 to 2/3 of
total irrigation water use in CA

30. Gg N /yr
Sources and Sinks of Nitrate

31. Agriculture and Energy
About 10 calories of energy is required
to produce 1 calorie of edible food
(35 calories for beef production);
• Roughly about 50% of this required energy goes towards
production of synthetic fertilizers and pesticides;
• Fertilizer manufacturing uses about 3-5 % of the world’s
annual natural gas production, and is equivalent to 1-2 %
of the world’s annual energy supply;
• Specifically, it takes nearly 1,000 m3 of natural gas to
produce one ton of ammonia,
with annual fertilizer production
of 178 million tons)

32. Nitrate use efficiency by crops
• Typically, half or more of the applied
nitrate fertilizer is not taken up by the crop;
• The rest ends up in the natural
environment: soil – surface/groundwater –
atmosphere
CHALLENGE: How would one monitor
nitrate leaching???

33. Efficient irrigation and fertigation practices
Across California
Objectives:
•Develop water & nitrate measurement techniques
•Recommend guidelines for improved irrigation
and nitrate management practices
Wireless Sensor Networks

34. Instruments list and functions:
1. Tensiometers: measures soil matric
potential, range: 850 - 0 mbar, individually-calibrated
pressure transducers
2. Decagon 5TE sensors: measures soil water
content, electrical conductivity, temperature
3. Decagon MPS-2 sensors: measures soil
matric potentials, range -4000 mbar – 0
4. Neutron Probe: measures soil water content,
large representative soil volume
5. Suction lysimeters : is used to collect soil
solution for nitrate analysis
6. Equilibrium-Tension Lysimeters: measures
drainage below the root zone and collect soil
solution samples for nitrate analysis
Multiple sensors at various depths and locations for
each treatment plot

35. Leaching measurement: Tensiometers below
40cm
140cm
200cm
A B
root zone – Darcy Flow
q
q = - K q H -
H
( )
B A
A B
A B z
-
- D
Improved Deep
Tensiometer

36. Enormous depth variation in soil texture/layering,
soil water retention,with corresponding
unsaturated hydraulic conductivity functions

37. Darcy Flow approach
Soil hydraulic properties
Laboratory methods
e.g. multi-step outflow experiments
Modelling based on measured parameters
e.g. soil moisture monitoring

38. Russell
Ranch
Sustainable
Agriculture
Facility
Photo: R. Ford Denison
Summer Winter
Fallow
Bell Bean
Triticale
Tomato/
Corn
Two soil types:
Rincon silty clay loam
Yolo silt loam
•3 replicates of each treatment

39. Russell Ranch –
Tomatoes
Treatments:
Winter fallow
Triticale
Bell beans

40. Daily leaching rates of water and nitrate in Bell Bean treatment
1st graph: Average water potential in soil profile (0 is soil saturation, the more negative the dryer the soil)
2nd graph: Soil water gradients (driving force for water movement) across a soil layer at 90-150 cm deep
3rd graph: Soil nitrate concentrations measured in soil solution in the 90-150 cm soil layer
4th graph: Daily vertical downward /upward fluxes of water (blue line on left Y axes) and nitrate (green line
on the right axes). Negative fluxes are downward and positive fluxes are upward. Most of the leaching of
water and nitrate seem to happen in the fall and early corn season.
Tomato Cover Crop Corn Cover Crop

41. Cumulative nitrate leaching in all three treatments
Vertical downward leaching of nitrate (negative values) throughout the crop rotations. Triticale showed to
be the most efficient in reducing the nitrate leaching below the root zone (150 cm deep). Note the
difference in nitrate leaching rate during different seasons in different treatments. While nitrate
continuously leached below the root zone of winter fallow in fall through corn season, it slowed down in
the two cover crop treatments.
Tomato Cover Crop Corn Cover Crop

42. Citrus sites: Orange Cove and Strathmore, CA
• Collecting water and nitrate movement data in the root zone and
below the root zone to capture seasonal variations in leaching and
following irrigation and fertigation events
• Where the tree roots are taking up water? Excavating and imaging
root distribution in depth and lateral distances from the trunk and
irrigation sprinklers
Wireless Sensor Networks

43. •Results - Mandarin
•43

44. Summary
Water and Nitrate Leaching/Monitoring
• Only relevant if deep surface is wet
• Deploy wireless sensor network at the field scale
• Develop deep tensiometers for accurate
gradient measurements
•Still need in situ soil nitrate sensor
Tuli, A., J.-B. Wei, B. D. Shaw, and J.W.
Hopmans. 2009. In situ monitoring of soil
solution nitrate: Proof of concept. Soil
Science Society Journal. 73(2). Doi:
10.2136/sssaj2008.0160 .

45. Required Research Needs
to meet food security challenge
• Develop improved water and nutrient use efficiency
methods for both rainfed and irrigated crop production
systems;
Field Research:
• Development of soil sensors using new technologies
(wireless, multi-functional, noninvasive, big data);
• Study impacts of soil environmental stresses (water,
nutrients, salinity, temperature) for both rainfed and
irrigated production systems.
Collaborate with plant & soil scientists, agronomists,
climate scientists, hydrologists, and others

48. Changes in CA Water Use, Irrigated Area (by crop type),
and Agricultural Income
1,400
1,200
1,000
800
600
400
200
0
CA population
30-40% is
groundwater
1960 1972 1980 1985 1992 2000 2005
Year -205 inflation adjusted dolars per acre fot aplied water
1 acrefoot ~ 1ML
1 MAF ~ 1 BCM~1 km3
CA agriculture has shown to be innovative and
flexible, and seek ways to increase income (yield) with
less water :
 Sustaining CA agriculture in an uncertain future,
Pacific Institute, 2009;
 Managing CA’s water - From conflict to reconciliation
Public Policy Institute of CA, 2011
 Agricultural issues Center, DANR, 2012
Total Developed Water Use in CA
Irrigated Area in CA
Adjusted Income/AF applied water