soils as a base for agriculture lee burras department of agronomy iowa state university global...

Soils as a base for Agriculture

Lee BurrasDepartment of AgronomyIowa State University

Global Agriculture Science & Policy InstituteFebruary 28, 2002

What are the potential constraints on soil productivity?

OutlineLee’s premisesWhat makes a soil productive?Where are the productive soils?Will the world’s soils stay productive?SummaryQuestions

Lee’s premises(1) We see what we know.

We think about what’s important to us.

(2) Soil and weather are the abiotic foundation of plant productivity.

(3) Plant production forms the basis for health, wealth, & environmental quality.

What controls soil productivity?

Water -infiltration, drainage, storageNutrients/toxins (12/17)Gas Exchange -CO2 out, O2 inStrength/rooting volumeWaste DisposalSeed/seedling nursery

Where are the productive soils?

What is the best soil? What soil order is it?

Where is the best soil?

Where are the productive soils?

We see what we know. The more we know, the more options we realize we have w/ the world’s soils.

Will the world’s soils stay productive?

What are the lessons from history?

What are the threats?

Are there opportunities?

What are the lessons from history?

Mesopotamia – “cradle of agriculture” – boomed then salinization & erosion.Greece – wheat & erosion olives & grapes Rome – wheat & erosion olives, grapes & Egypt.China – 3,000 years of agriculture on loess, soil conservation 2000 BP b/c 1.2 billion tons erosion, today 2.4 billion tons.Cotton production – eastern USA for 150 years.

Summary – soil productivity typically finite.

What are some threats?Finite arable land: 1.1 billion hectares

1961 0.32 ha/p; today 0.15 ha/p; 2050 0.12 ha/p

Erosion – today 12-40 Mg/ha 30% agricultural lands irreversibly damaged.Desertification – e.g., 27% China affected w/ new 2500 km2/yr. Salinization- affects 20% of world’s 250+ million hectares of irrigated lands.Contamination w/ heavy metals.Urbanization and other competing uses.Problematic off-site issues & competing uses.

Threats? Think little things.Compaction or loss of porosity.Loss soil organic matter.Loss CEC other buffering potential. Doolittle Prairie –

e.g., 10% reduction in pore volume

= 152 m3/ha

= 2200 ft3/ac

-less gas exchange, water storage, root volume; poorer nursery.

-water quality & quantity, air quality

Is continued productivity possible?Yes, very much so.

Most soils highly buffered – intense use possible provided managed vis-à-vis limitations.Many soils under-managed wrt surface area, sunlight, nutrients, water – Why not intercrop? Tremendous capacity to produce calories – e.g., Iowa’s 12 million hectares 500 trillion kcal.

We know how to manage for long-term soil quality and immediate production – provided we use what we know.

Summary – constraints on productivity?

We forget there are 6 roles of soil in plant growth. We only manage ones we know.We forget there isn’t any new land.Off-site issues huge.

On the plus side, we know how to learn from other’s mistakes. So, knowledge is key.

Questions and/or comments?