Lecture 11Lecture 11Agriculture and the EnvironmentAgriculture and the Environment

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Agriculture and the EnvironmentAgriculture and the Environment

95% of human population’s protein & most of its calories are 95% of human population’s protein & most of its calories are obtained from traditional land-based agriculture of crops and obtained from traditional land-based agriculture of crops and livestocklivestock

CropsCrops World’s food is provided by only 14 crop speciesWorld’s food is provided by only 14 crop species Six cropsSix crops provide >80% of the total caloriesprovide >80% of the total calories

Types of CropsTypes of Crops Cash cropsCash crops– grown to be sold or traded, e.g. jute– grown to be sold or traded, e.g. jute Subsistence cropsSubsistence crops– used directly for food by the farmer or – used directly for food by the farmer or

sold locally, e.g., ricesold locally, e.g., rice

Seasonal crops of BangladeshSeasonal crops of Bangladesh

Mainly two seasonsMainly two seasons– – Rabi and KharifRabi and Kharif Kharif – Kharif 1 & Kharif 2Kharif – Kharif 1 & Kharif 2 Overlapping occursOverlapping occurs Many are grown in all seasonsMany are grown in all seasons Crops are dividedCrops are divided into cereals, pulses, fiber crops, oil seeds, into cereals, pulses, fiber crops, oil seeds,

root crops, vegetables, spice crops, fruit cropsroot crops, vegetables, spice crops, fruit crops Rice and maize are grown in all seasons whereas wheat is Rice and maize are grown in all seasons whereas wheat is

grown in Rabi season (rainfed & irrigated), barley & kaon in grown in Rabi season (rainfed & irrigated), barley & kaon in Rabi seasonRabi season

Lentil, khesari, chickpea, balckgram all pulses grown in Rabi Lentil, khesari, chickpea, balckgram all pulses grown in Rabi seasonseason

Mungbean, another pulse crop grown in both Rabi & Kharif Mungbean, another pulse crop grown in both Rabi & Kharif seasonsseasons

SoilSoil Collection of natural body occupying portion of the Earth’s crust Collection of natural body occupying portion of the Earth’s crust

that supports plant growth which have acquired properties due to that supports plant growth which have acquired properties due to the integrated action of the integrated action of climate climate and and vegetationvegetation upon upon parent parent materialmaterial as conditioned by as conditioned by reliefrelief over a period of over a period of timetime

Four major componentsFour major components of soil are air (25%), water (25%), of soil are air (25%), water (25%), mineral matter (45%), and organic matter (5% by volume)mineral matter (45%), and organic matter (5% by volume)

Type of soil at a particular site depends on soil-forming factors :Type of soil at a particular site depends on soil-forming factors :

(1) Parent material, (2) Climate, (3) Topography, (4) Living (1) Parent material, (2) Climate, (3) Topography, (4) Living organism, (5) Timeorganism, (5) Time

Soil fertilitySoil fertility refers to the capacity of a soil to supply the nutrients refers to the capacity of a soil to supply the nutrients and physical properties necessary for plant growth and physical properties necessary for plant growth

Ironically, agriculture depends heavily on soil quality, but Ironically, agriculture depends heavily on soil quality, but agriculture can lead to a decline in that qualityagriculture can lead to a decline in that quality — — a dilemmaa dilemma

SoilSoil

A A high-quality soil hashigh-quality soil has all the nutrient elements, a physical structure all the nutrient elements, a physical structure conducive to plant growth, and high organic matter contentconducive to plant growth, and high organic matter content

Organic matter includes dead, partially or completely decomposed Organic matter includes dead, partially or completely decomposed crop or plant and animal remains, forest litter, leaves, twigs, etc crop or plant and animal remains, forest litter, leaves, twigs, etc

OM is the OM is the store housestore house of nutrients and p of nutrients and providesrovides good structuregood structure

Good structure is Good structure is key key to soil fertilityto soil fertility

When original vegetation is cleared, soil becomes exposed to more When original vegetation is cleared, soil becomes exposed to more sunshine and oxidation resultssunshine and oxidation results

Rapid Rapid oxidation oxidation results decline in OMresults decline in OM

Soil begins to Soil begins to lose fertilitylose fertility

Soils also lose fertility through surface and subsurface Soils also lose fertility through surface and subsurface runoff of runoff of dissolved nutrientsdissolved nutrients

Loss of fertility is Loss of fertility is fasterfaster in warmer & wetter climates than it is in colder in warmer & wetter climates than it is in colder or drier climatesor drier climates

Soil Plowing & ErosionSoil Plowing & Erosion PlowingPlowing is the shattering soil uniformly with partial to is the shattering soil uniformly with partial to

complete inversioncomplete inversion Plowing opens the soil toPlowing opens the soil to erosionerosion even more than removal of even more than removal of

the original vegetationthe original vegetation ErosionErosion is the wearing away and transportation of land is the wearing away and transportation of land

surface by running water, wind, ice, or other natural agents surface by running water, wind, ice, or other natural agents Soil loosened by plowing can blow by Soil loosened by plowing can blow by windwind when dry & wash when dry & wash

away with away with rain waterrain water Plowed lands loose upper layers containing the Plowed lands loose upper layers containing the most fertilemost fertile

organic matterorganic matter The less OM present in the soil, the The less OM present in the soil, the more vulnerablemore vulnerable the soil the soil

is is toto further further erosionerosion Once erosion starts, the process can easily accelerateOnce erosion starts, the process can easily accelerate

Tillage operation in soil to receive the crop

Soil Erosion

Soil Plowing & ErosionSoil Plowing & Erosion Population pressuresPopulation pressures have led to have led to overgrazingovergrazing, , deforestation, deforestation,

destructive crop practicesdestructive crop practices like clearing & burning steep, forested like clearing & burning steep, forested slopes and plowing grasslandsslopes and plowing grasslands

All these activities All these activities degradedegrade or remove natural vegetation causing or remove natural vegetation causing the underlying soil to become much the underlying soil to become much more susceptiblemore susceptible to the to the destructive action of destructive action of erosionerosion

The result is a vicious downward cycle of deterioration—The result is a vicious downward cycle of deterioration— land land degradationdegradation

Such land degradation results in a reduced productive potential Such land degradation results in a reduced productive potential and a diminished capacity to provide benefits to humanityand a diminished capacity to provide benefits to humanity

All forms of agriculture lead to soil lossAll forms of agriculture lead to soil loss Loss varies with the crops and the methods of agricultureLoss varies with the crops and the methods of agriculture Land used for row crops & small grains Land used for row crops & small grains without without conservation conservation

practicespractices result in greater erosion loss result in greater erosion loss Worldwide, erosion removes about Worldwide, erosion removes about 25.4 billion tonnes25.4 billion tonnes of soil of soil

each yeareach year

Sediment DamageSediment Damage

Much of the eroded soil Much of the eroded soil ends up in waterwaysends up in waterways causing causing downstream downstream sedimentationsedimentation

Sediments Sediments fill infill in productive waterwaysproductive waterways

Nitrate, ammonia, Nitrate, ammonia, phosphates, & other phosphates, & other fertilizers carried by fertilizers carried by sediments can cause sediments can cause eutrophicationeutrophication in in downstream watersdownstream waters

Making Soils Sustainable: Contour PlowingMaking Soils Sustainable: Contour Plowing

With good management soil is continuously formed at the rate of With good management soil is continuously formed at the rate of 1 mm/yr1 mm/yr

Ideal farming would result in soil loss no greater than the Ideal farming would result in soil loss no greater than the formation of new soilformation of new soil

One way to counter soil erosion is to One way to counter soil erosion is to promote new soil formationpromote new soil formation Another way to counter erosion from plowing is Another way to counter erosion from plowing is contour plowingcontour plowing In In contour plowingcontour plowing, the land is plowed along the contours , the land is plowed along the contours

perpendicular to the slope and as much in the horizontal plane perpendicular to the slope and as much in the horizontal plane as possibleas possible

Contour plowing is the single most effective method for reducing Contour plowing is the single most effective method for reducing soil erosion loss owing to water runoffsoil erosion loss owing to water runoff

Contour plowing

Windbreak

Making Soils Sustainable: Mixed, Strip, Terracing, Making Soils Sustainable: Mixed, Strip, Terracing, Rotation, No-till agricultureRotation, No-till agriculture

Other practicesOther practices that can aid in the sustainability of soils include that can aid in the sustainability of soils include mixed cropping, strip cropping, terracing, crop rotationmixed cropping, strip cropping, terracing, crop rotation

An even An even more efficient techniquemore efficient technique to slow erosion is to slow erosion is to avoid to avoid plowingplowing altogether altogether

No –till agriculture or conservation tillageNo –till agriculture or conservation tillage is a recent form of is a recent form of combination of farming practices that includes combination of farming practices that includes not plowingnot plowing the the land, using land, using herbicidesherbicides to keep down the weeds to keep down the weeds

In In no-tillno-till agriculture the land is left agriculture the land is left unplowedunplowed most years most years

Mixed cropping

SteepTerracing

Strip cropping

Thai tea plantation

Conservation Tillage

No Tillage

Mulch Tillage/Conservation tillageMulch Tillage/Conservation tillage

In mulch tillage In mulch tillage plant residues or other materials are left to plant residues or other materials are left to cover the surface and allowed to decay in placecover the surface and allowed to decay in place

Besides soil conservation, conservation tillage Besides soil conservation, conservation tillage suppresses & suppresses & controls the weedscontrols the weeds

These practices greatly These practices greatly (a)(a) reduce soil & water loss reduce soil & water loss (b)(b) reduce traffic operations over the field reduce traffic operations over the field (c)(c) reduce the use of fuel reduce the use of fuel (d)(d) reduce soil compaction reduce soil compaction (e)(e) increase profit increase profit

Approach to Sustainable AgricultureApproach to Sustainable Agriculture

Population pressuresPopulation pressures & the & the availability of arable landavailability of arable land are the are the most important factors determining sustainability of most important factors determining sustainability of agriculture agriculture

Maintenance and management of soil fertility is central to the Maintenance and management of soil fertility is central to the development of sustainable food production systemsdevelopment of sustainable food production systems

The wisest approach to sustainable agriculture involves The wisest approach to sustainable agriculture involves a combination of different kinds of land use as a combination of different kinds of land use as

Use best agricultural lands for cropsUse best agricultural lands for crops Poorer lands for pastures and rangelandsPoorer lands for pastures and rangelands Avoid using best lands for grain production for animal feedAvoid using best lands for grain production for animal feed

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