Weed management in conservation agricultural systems

1. Presented by:
Kommireddy Poojitha
PALB 8044
Dpt. of Agronomy
Weed Management in Conservation
Agricultural Systems

2. Weed management
Weed management is the application of certain
principles and suitable methods that will improve
the vigor and uniform stand of the crop and at the
same time discourages the invasion and growth of
weeds.
It encompasses all the aspects of prevention,
eradication and control by regulated use, restricting
invasion, suppression of growth, prevention of seed
production and complete destruction.

3. “CA is a concept for resource saving agricultural crop
production that strives to achieve acceptable profits together
with high and sustained production levels while concurrently
conserving the environment (FAO).
CA is based on enhancing natural biological process
above and below the ground. Interventions such as mechanical
soil tillage are reduced to an absolute minimum, and the use of
external inputs such as agrochemicals and nutrients of mineral
or organic origin are applied at an optimum level and in a way
and quantity that does not interfere with, or disrupt, the
biological process.
Conservation agriculture

4. Principles of conservation agriculture
Intensity of soil disturbance
Crop rotation
Conventionalagriculture
Conventional Minimum
Tillage
Direct
seeding
Sustainable agriculture
Surface crop retention

5. Weed management strategies in conservation
agriculture
 Preventive weed management
 Tillage
 Cover crops
 Crop residues
 Crop rotation
 Crop type and cultivar
 Adjusting crop planting date
 Seed rate and spacing
 Resource management
 Chemical weed management
 Herbicide resistant crops
 Integrated weed management

6. Preventive weed management
 Preventive weed management focuses on impeding the
introduction of new or additional weed populations and
reducing the overall emergence and propagation of
weeds in the field.
 It is easier and less costly than control or eradication
attempts.
 The major preventive measures include:
I. Quality Planting Material and Clean Equipment
Use of good quality crop seeds,
Clean machinery or tools,
Weed seed screens to filter irrigation water
Fully decomposed manure

7. II. Reduced Weed Seed Bank
Seed predation
Beetle strips (Dactylis and Phleum spp.)
Seed decay
Increased germination
Solarization
III. Prevention of Weed Seed Production and
Shedding
Harvest weed seed control
Weed header

8. Tillage
 Tillage itself provides germination stimulus for weeds
requiring light flashes, scarification, fluctuating
temperatures, ambient CO2 concentrations, and/or
higher nitrate concentrations to break dormancy.
 A low-soil-disturbance single-disc system retained
more than 75 % of the weed seeds in the top 1-cm soil
layer (Chauhan et al., 2006). A seed is on the soil
surface, it is very likely to suffer one of the two fates:
germination or predation.

9. Cover crops and Crop residues
 Cover crops and crop residues causes weed suppression
through physical as well as chemical changes in the seed
environment.
 The main physical effects include a reduction in light, soil
surface insulation and by competition.
 Crops and its Residues decreases weed seed germination
due to insufficient light-availability and also reduces seedling
emergence.
 Surface residue decreases the daily maximum soil
temperature and reduces the fluctuation of temperature.
Some weed species germination is enhanced by larger
temperature fluctuations are affected.
 Some cover crops and residues change the chemical
environment of the weed seed via allelopathy.

10. Crop rotation
 Diversified crop rotation, as a main component of CA systems,
can increase yield potential by influencing weeds, plant
diseases, root distribution, moisture utilization and nutrient
availability.
 Rotating crops will rotate selection pressures, preventing one
weed from being repeatedly successful and thus preventing its
establishment.
 Rotations alter selection pressures via three main mechanisms
including
(i) Altering managements (e.g., timing of field activities,
herbicides)
(ii) Varying patterns of resource competition
(iii) Allelopathy
 Best method for crop bound and associated weeds.

11. Crop type and cultivar
Crop:
 Crop choice could be an important tool for the weed
control in CA.
 For example, wild oat infests both spring wheat and
barley but, barley is a more competitive crop than wheat.
Cultivar:
 In groundnut yield losses are more in bunch type than
spreading type.
 In wheat, HD 2285 is more competitive than HD2009 and
recorded only 16.5 % reduction in yield.

12. Adjusting the crop planting date
 Due to dormancy processes, many weeds germinate during
specific seasons. If the approximate date of emergence is
known for problem weeds, crop planting dates can be
adjusted so that either
(i) The crop emerges before the weeds for a competitive
advantage or
(ii) Weeds are allowed to germinate and are controlled
before or during crop planting.
 The potential weed suppression offered by early crop
planting is demonstrated by the case of Phalaris minor in
rice-wheat systems of the Indo-Gangetic plains. Adoption of
NT permitted wheat crops to be planted 1–2 weeks earlier,
allowing the crop to establish before emergence of the still
dormant Phalaris minor.

13. Seed rate and spacing
 Higher seeding rate and narrow-row spacing are known
strategies for increasing crop tolerance to weeds.
 Biomass and yield of wild oat were reduced by 20 %
when the sowing rate of winter wheat was increased
from 175 to 280 plants m−2.
 There are some limitations to narrow-row crop
production in regard to weed management
Ex: In cotton narrow row spacing causes difficulty in
inter row cultivation, post emergence directed
herbicide sprays and hooded sprayer applications.

14. Resource management
Management practices that increase the competitive
ability of crops with weeds are:
 Fertilizers :
 The greatest competition between plants and weeds is
usually for nitrogen.
 N fertilizer (ammonium) is known to break the dormancy
of certain weed species and thus may directly affect
weed infestation densities.
 Fertilizer placed in narrow bands below the soil surface
compared with being surface broadcast has been found
to reduce the competitive ability of wild oat.
 Irrigation:
 Drip irrigation is advantageous over other methods.

15. Chemical weed management
 Herbicides have an important role in weed control under CA
systems.
 Herbicides are effective weed control measures and offer diverse
benefits, such as saving labor and fuel cost, reducing soil erosion,
saving energy, increasing crop production, reducing the cost of
farming, allowing flexibility in weed management and tackling
difficult-to-control weeds.
 Before planting, the need for non selective post emergence
herbicides (e.g., glyphosate, paraquat, and glufosinate) to control
weeds before planting crops would become inevitable.
 Stale seed bed is a promising approach for killing weeds before
planting in CA systems.
 Crop residues can intercept from 15 to 80 % of the applied
herbicides, and this may result in reduced efficacy of herbicides in
CA systems.

16. Biotechnological approaches
1) Herbicide resistant crops
 HRCs encourage safe use of non selective herbicides for
selective weed control.
 They facilitate wider window application.

2) Parasitic weed resistant crop variety
 Striga resistant sorghum and maize were developed by
using biotechnological tools.
Herbicide resistant crop Herbicide resisted
Canola Glyphosate, Glufosinate
Corn Glyphosate, Glufosinate
Soybean Sulfonyl ureas, Glyphosate, Glufosinate
Cotton Bromoxynil, Glyphosate, Glufosinate

17. Integrated weed management
 The commonly accepted best approach to manage weeds is
to follow an integrated weed management strategy
comprising the combined use of two or more available and
effective technologies.
 Combining good agronomic practices, timeliness of
operations, fertilizer and water management, and retaining
crop residues on the soil surface improve the weed control
efficiency of applied herbicides and competitiveness
against weeds.

18. Thank you