1. ROW SPACING & PLANT POPULATION AS IPM TOOLS FOR NO-TILL SILAGE CORN
IN CENTRAL CALIFORNIA
Anil Shrestha
Statewide IPM Program
University of California
Kearney Ag. Center, Parlier
Carol Frate
University of California Cooperative Extension Tulare County
Charles Summers
University of California, Davis

2. Conservation Tillage (CT) in California
CT is fairly new for California
Less than 2% of annual crop acreage
In California, CT focuses more on reducing number of tillage passes than on preserving surface residues.

3. Reasons for low adoption of CT in California
Lack of locally available CT equipment and information
Inexperience with CT techniques
Predominance of surface or gravity irrigation systems
Tillage-intensive systems developed for several decades are highly productive
Diversity of crop types and cropping systems

4. Current Interest in CT in California
NRCS Environmental Quality Incentives Program (EQIP)
Rising fuel prices
Conversion to overhead irrigation systems
Extension activities of CT Workgroup
Environmental regulations
Opportunities for triple cropping*

5. CT activity is fairly limited to Research/Demonstration by CT
Workgroup with grower partners
However, there is new interest in CT ……

6. Coupling overhead irrigation systems with
CT: A means for optimizing cheap, efficient and resource-conserving production systems?

7. California Waste Discharge Permit Requirement
General Order for Milk Cow Dairies
-Limits field application of dairy waste nutrients to 140%
of expected crop uptake

8. Dairy forage triple-cropping as a means to increase forage
production and nutrient uptake
Nutrients can be applied
to the third crop, planting
of which is enabled by CT

9. Harvesting winter forage wheat, strip-tilling
and planting corn, Tipton, CA, May 2005

10. Strip-till planting corn in wheat residue

11. Strip-till planting corn in wheat residue

12. No-till planting sorhgum-sudan in corn residue

13. Post-plant irrigation of sorhgum-sudan

14. conventional tillage + furrows for irrigation
Traditional corn –
conventional tillage + furrows for irrigation

15. Factors enabling CT Planting equipment that can do different spacings
GPS and flat planting
No tractors in the field
Irrigate flat – no furrows
Pesticide application by air
Harvest equipment that is flexible

16. Studies elsewhere have found that:
Narrow rows (38 cm) and higher corn density reduced the need for long-term residual herbicides
Corn yields increased by 10-15% in narrow rows
HOWEVER, these results have not been consistent.
Climatic conditions, rainfed cropping systems,
dominant weed species have influences

17. Rationale Narrow rows close canopy earlier then the wide
rows and shade later-emerging weeds
Germination of some weed seeds that require
light may be prevented or reduced by shading
Increased crop density may help the crops
compete better for resources
Light levels under the crop canopy may influence
insect pest dynamics

18. Objective
Evaluate the effect of corn row spacing (38 vs 76 cm) and plant population (69000, 86000, plants ha-1) on light attenuation patterns, weed populations, insect dynamics, and crop yield

19. Experimental details Harvested winter forage Planted
May 13 & 14th , 2004 & 2005
Variety: DK C66-80 (RR)
10 row JD No-Till Planter, used GPS
Split-plot with row spacing as main plot and plant population as sub plots
4 replications
Plot size – 7.6 m by 402 m
Glyphosate aerially applied in June
Mechanically harvested in September

20. Measurements
Weekly measurements on PAR above and below the corn canopy
Stalk diameter
Weed populations mid-season & at harvest
Weed biomass at harvest
Insect (corn leaf hopper, aphid, leafminer)
Crop yield

21. Results

22. Distribution of weed species in June (before herbicide application)

23. Light interception by corn canopy
2004
W = 76 cm
N = 38 cm
L = 69000
M = 86000
H = 10400

24. Light interception by corn canopy
2005
38-cm rows
closed canopy
6-13 days
earlier than
the 76-cm
rows

25. Weed densities- July 2004 Spacing P = 0.10 Population P = 0.95
Spacing*Pop
P = 0.55

26. Weed densities- July 2005 Spacing P = 0.005 Population P = 0.03
Spacing*Pop
P =

27. Weed biomass at corn harvest
2004

28. Weed biomass at corn harvest
2005

29. Narrow-rows suppressed weeds better than wide-rows
76 cm
36 cm

30. Insects monitored Monitored June to August using sticky traps
Corn leafhopper (Dalbulus maidis)
Corn leaf aphid (Rhopalosiphum maidis)
Monitored June
to August using
sticky traps
Corn leafminer (Agromyza sp.)

31. Insect population dynamics
Plant populations affected insect populations but row spacing did not
Corn leaf hopper densities were about 3/card in the high corn population plots compared to 6-7/card in the low population plots
Aphid numbers were about 80/leaf in low population plots compared to <50/leaf in high population plots
Leafminer populations were 2-3 times greater in the low corn population plots compared to the high population plots

32. Corn dry matter yield
Adjusted to 70% moisture

33. Stalk diameter 76-cm rows 38-cm rows 2004 - 2.4 cm 2.6 cm 2.4 cm
P = 0.01
P < 0.001

34. Conclusions
Preceding crops in the rotation may be the predominant weed in no-till systems
38-cm rows intercepted more light and closed canopy 6-13 days earlier than the 76-cm rows
Weed density at mid-season was lower in the 38- than the 76-cm rows in one year of the study
Weed biomass at the end of the season was lower in the 38- than in the 76-cm rows in both years
Plant population had no effect on light interception or weed dynamics

35. Conclusions
Insect populations were lower in the high plant population plots regardless of row spacing
Corn stalk diameter was greater in the 38- than in the 76-cm rows
Crop yield was not affected by row spacing or plant population
Some caveats:
- Dairy growers usually rely on custom applicators for herbicide treatments so early canopy closure may not be desirable for aerial application of a herbicide like glyphosate
- Growers do not see any immediate benefit to growing corn in 38-cm rows but some are interested in twin-rows