new LECTURE 3-converted.pdf

Lecture of Fundamentals of Agronomy

1. Lecture 3
Tilth, its definition, characteristics of ideal
tilthand modern concepts of tillage

2. Definition of tilthor soil tilth:
‘Itisthephysicalconditionofsoilresultingfromtillage&saidtobegood
whenthesoilissoft,friableandproperlyaerated.’
Characteristics of good soil tilth:
Itshouldhavehigher%oflargeraggregates(morethan5mmdiameter)
forirrigatedfarming.
Itshouldhavehigher%ofsmalleraggregates(1-2mmdiameter)fordry-
landfarming.
Goodsoiltilthshouldbeporous&hasfreedrainageuptowatertable.
Micro-pores(capillary)&Macro-pores(non-capillary)shouldbeinequal
proportion.
Thesoilparticlesshouldnotbeeasilyerodedbywaterorwind.
Soilshouldnotbestickywhenmoist.
Soilshouldpermiteasyinfiltrationofwater.

3. Modern concepts in tillage:
Conventional tillage involves primary tillage to break open and turn the soil
followed by secondary tillage to obtain seed bed for sowing or planting.
Continuous use of heavy ploughs create hard pan in the subsoil, results in
poor infiltration.
It is more susceptible to run-off and erosion.
It is capital intensive and increase soil degradation.
To avoid these ill effects, modern concepts on tillage is in rule

4. 1. Minimum tillage:
It aims at reducing tillage operations to the minimum necessity for ensuring a
good seed bed.
The advantages of minimum tillage over conventional tillage are:
1.The cost and time for field preparation is reduced by reducing the
number of field operations.
2.Soil compaction is comparatively less.
3.Soil structure is not destroyed.
4.Water loss through runoff and erosion is minimum.
5.Water storage in the plough layer is increased.
Tillage can be reduced in 2 ways:
1.By omitting operations which do not give much benefit when compared
to the cost.
2.By combining agricultural operations like seeding and fertilizer
application.

5. Theminimumtillagesystemscanbegroupedintothefollowing
categories,
1.Rowzonetillage:Primarytillageisdonewithmouldboardploughin
theentireareaofthefield;secondarytillageoperationslikediscing
andharrowingarereducedanddoneonlyinrowzone.
2.Ploughplanttillage:Aftertheprimarytillage,aspecialplanteris
usedforsowing.Inonerunoverthefield,therowzoneispulverized
andseedsaresownbytheplanter
3.Wheeltracktillage:Primaryploughingisdoneasusual.Tractoris
usedforsowing;thewheelsofthetractorpulverizetherowzonein
whichplantingisdone.
Inallthesesystems,primarytillageisasusual.However,secondary
tillageisreplacedbydirectsowinginwhichsownseediscoveredin
therowzonewiththeequipmentusedforsowing.

6. 2. Zero tillage (No tillage):
Inthis,newcropisplantedintheresiduesofthepreviouscropwithoutany
priorsoiltillageorseedbedpreparationanditispossiblewhenalltheweeds
arecontrolledbytheuseofherbicides.
Zerotillageisapplicableforsoilswithacoarsetexturedsurfacehorizon,good
internaldrainage,highbiologicalactivityofsoilfauna,favourableinitialsoil
structureandanadequatequantityofcropresidueasmulch.
TheseconditionsaregenerallyfoundinAlfisols,OxisolsandUltisolsinthe
humidandsub-humidtropics.

7. Advantages of zero tillage:
Zero tilled soils are homogenous in structure with more number of earthworms.
Organic matter content increases due to less mineralization.
Surface run-off is reduced due to presence of mulch.
Disadvantages of zero tillage:
Higher amount of nitrogen has to be applied for mineralization of organic matter
in zero tillage.
Perennial weeds may be a problem.
High number of volunteer plants and buildup of pests.

8. 3. Stubble mulch tillage or stubble mulch farming :
Soilisprotectedatalltimeseitherbygrowingacroporbyleavingthecrop
residuesonthesurfaceduringfallowperiods.
Sweepsorbladesaregenerallyusedtocutthesoilupto12to15cmdepthin
thefirstoperationafterharvestanddepthofcutisreducedduring
subsequentoperations.
Whenlargeamountofresiduesarepresent,adisctypeimplementisusedfor
thefirstoperationtoincorporatesomeoftheresiduesintothesoil.
Thishastensthedecompositionbutstillkeepsenoughresiduesontopsoil.
Disadvantagesofstubblemulchfarming
Theresiduesleftonthesurfaceinterferewithseedbedpreparationand
sowingoperations.
Thetraditionaltillageandsowingimplementsorequipmentsarenot
suitableundertheseconditions.

9. 4. Conservation tillage:
✓Themajorobjectiveistoconservesoilandsoilmoisture.
✓Itisasystemoftillageinwhichorganicresiduesarenotinvertedintothesoil
suchthattheyremainonsurfaceasprotectivecoveragainsterosionand
evaporationlossesofsoilmoisture.
✓Ifstubbleformstheprotectivecoveronthesurface,itisusuallyreferredtoas
stubblemulchtillage.
✓Theresiduesleftonsoilsurfaceinterferewithseedbedpreparationand
sowingoperations.
✓Itisayearroundsystemofmanagingplantresiduewithimplementsthat
undercutresidues,lossesthesoilandkillstheweeds.
✓Advantages
1.Energyconservationthroughreducedtillageoperations.
2.Improvethesoilphysicalproperties.
3.Reducethewaterrunofffromfields.