Wilson E. Judice and James L. Griffin
At one time the Louisiana sugarcane crop was harvested using mechanical whole stalk harvesters, where stalks were piled in the field and burned to remove leaves before transporting to the mill. Beginning in the mid 1990s, growers shifted to chopper harvesters, where stalks are cut into billets, loaded directly into wagons and transported to the mill.
When sugarcane is harvested green using the chopper harvester, crop residue (tops and leaves) is deposited on the soil surface. Although the crop residue may provide suppression of weeds, the residue can also delay sugarcane emergence and reduce early season growth and yield. When feasible, crop residue remaining in the field is burned. Because of environmental and social concerns related to burning, other strategies of residue removal are being investigated.
A residue management/tillage study was conducted on privately owned farms at St. Gabriel, Youngsville and Franklin. LCP 85-384 sugarcane was harvested using a chopper harvester. Crop residue ranged from 4.6 to 8.7 tons per acre dry weight. Crop residue was removed within three weeks after harvest by burning or by using a Sunco Trash Tiger. This tractor-drawn implement is equipped with concave shaped notched disks (four per row) that rake the residue off the row top (approximately 30 inches wide) and into the row middles.
The other treatment factors were spring tillage in mid to late March and layby tillage in mid to late May. For the tillage operations, the row sides and middles were mechanically worked using disk gangs with an area approximately 24 inches wide on the row top left undisturbed.
In a residue removal/timing study, experiments were conducted at the LSU AgCenter’s Sugar Research Station, St. Gabriel, and at a privately owned farm in Youngsville. LCP 85-384 sugarcane was harvested with a chopper harvester in December. Crop residue on the soil surface was 3.1 tons per acre dry weight at St. Gabriel and 3.5 tons per acre dry weight at Youngsville. The first treatment factor was timing of residue removal by burning or by mechanical removal using a Trash Tiger. See Table 1.
The burn treatment represented the preferred grower practice. At the March removal using the Trash Tiger, sugarcane had begun to emerge from the winter dormant period. Therefore, this treatment would represent a worst case scenario in regard to the effect that residue could have on sugarcane emergence and growth. The second factor consisted of spring tillage in mid March each year.
In both studies herbicides were applied immediately after the spring tillage operation and again after the layby tillage operation. Crop residue remaining on the soil surface in March just before sugarcane emergence was determined visually as percent ground cover using a scale of zero to 100 percent.
No attempt was made to quantify biomass of residue on the soil surface or thickness of the crop residue mat. Weed ground cover was determined in March to evaluate the effect of sugarcane residue on winter weeds. In both studies sugarcane growth and yield response to the crop residue management treatments were the same for the conventional and reduced tillage programs.
For the residue management/tillage study, there was no more than 14 percent ground cover of crop residue on the row in March where residue had been removed by burning or mechanically using the Trash Tiger. Crop residue ground cover was 90 percent where residue was not removed. Winter weed ground cover on the row top in March averaged 14 percent for the burn treatment and 17 percent for the mechanical removal treatment compared with 7 percent where crop residue was not removed. Even though the sugarcane residue suppressed winter weeds somewhat, a late winter/ early spring herbicide treatment would still be needed. Sugarcane shoot population in April was reduced 6 percent when sugarcane residue was not removed.
Sugarcane height in June for the burn and mechanical removal treatments averaged 4 inches taller than for the no removal treatment. By August, however, there were no differences in sugarcane stalk height among the residue management treatments. Sugarcane stalk population in August and sugarcane yield were each equivalent regardless of residue management treatment.
Because of differences in recoverable sugar per ton among the residue management treatments, however, sugar yield was affected. Averaged across locations and tillage programs, sugar yield was equal for the burn and mechanical residue removal treatments and averaged 600 pounds per acre more (8.6 percent increase) than when residue was not removed. Although no economic analysis for the crop residue management programs was conducted, mechanical removal of residue would cost consider ably more than burning, although there would be some cost associated with burning. Elimination of spring tillage and layby tillage did not hinder sugarcane growth or yield when compared with a full season tillage program.
For the residue removal/timing study, winter weed ground cover in mid- March on the row top was 5 percent when crop residue was not removed but was 10 percent when crop residue was burned in December and 18 percent when crop residue was removed mechanically in December. Crop residue ground cover in mid-March was 79 percent when residue had not been removed and had remained on the soil surface since harvest. This is in contrast to 33 percent to 37 percent crop residue ground cover when residue was removed mechanically in December, January or February and 12 percent when residue was burned in December.
Sugarcane height in June was equal when crop residue was removed in December by burning or mechanically using the Trash Tiger (Table 1). Sugarcane height in August was equivalent when residue was removed in December, January and February and averaged 8 percent more than when residue was removed in March. Sugarcane yield did not differ when crop residue was either mechanically removed or burned in December (32.8 tons per acre average). When residue removal was delayed until February, however, sugar yield was reduced 11 percent (Table 1). Sugar yield was equivalent when crop residue was burned or mechanically removed in December and averaged 7,740 pounds per acre. Compared with residue removal in December, delaying mechanical removal of residue until February or March decreased yields an average of around 1,000 pounds of sugar per acre (13 percent decrease).
In sugarcane harvested using a combine, yield of the ratoon crop is maximized when crop residue is removed from the row top as soon after harvest as possible and before the end of January. The Trash Tiger did an excellent job of removing residue from the top of the sugarcane rows and would be an alternative to burning in smoke-sensitive areas. Even though residue in the row middles was essentially doubled when residue was removed mechanically, the normal spring tillage operation and fertilizer application were not hindered. It would be especially important when residue is removed mechanically that drains be cleared to allow for water runoff from fields. A reduced tillage program can be successful both when crop residue is removed by burning or by mechanical means. Timely mechanical removal of crop residue in combination with a reduced tillage program can decrease cost of production by eliminating tillage operations without sacrificing yield and can help to reduce soil loss.
Wilson E. Judice, former Graduate Research Assistant, and James L. Griffin, Lee Mason LSU Alumni Association Professor, School of Plant, Environmental & Soil Sciences, LSU AgCenter, Baton Rouge, La.
(This article was published in the spring 2008 issue of Louisiana Agriculture.)