Albert J. Orgeron, Kenneth Gravois and Paul White

Louisiana farmers grow many of the annual staple crops found across the United States, including corn, soybean, cotton and grain sorghum. However, Louisiana’s No. 1 valued row crop is sugarcane, a perennial that is only grown in two other states, Florida and Texas. Sugarcane was grown on 500,000 acres in 2020, adding more than $3 billion to the state’s economy.

Fields where sugarcane is planted are left fallow following the last harvest. To start a sugarcane crop, stalks of sugarcane are planted in an open furrow on bedded rows in these fallow fields (Photo 1). From this initial planting, three to five subsequent harvests are made each year. Research has shown the greatest potential for soil losses in sugarcane production occur during these two distinct periods within the production cycle: the fallow period and to a lesser extent during the fall and spring in newly planted fields.

Cover crops have been utilized throughout the United States in many annual row crops. A cover crop can stimulate microorganism growth in the soil, control weeds, regulate soil temperature, and reduce soil erosion. Long-term effects include increasing soil organic matter, which improves overall soil fertility. Evaluating the use of cover crops in Louisiana sugarcane production was our project objective.

Fallow Period

The fallow period often spans several months between final harvest (October or November in the previous year) and planting of new sugarcane (August to September of the planting year). Soil left bare is highly erodible because of the intensive tillage necessary to terminate the previous crop and the desire to keep the ground as weed-free as possible by periodic to frequent tillage operations.

Several cover crop options available to Louisiana sugarcane farmers can minimize erosion, provide additional income and improve soil health. Cover crops should be planted in April or May to allow for sufficient growth prior to terminating. Soybeans are the most common cover crop and can provide an additional source of revenue. Soybean production using glyphosate-resistant soybean seed also provides an opportunity to control itchgrass and bermudagrass using glyphosate.

Iron clay cowpea or sunn hemp (Photo 2) can be planted as cover crops during fallow periods as well. These cover crops are seeded at rates between 10 and 50 pounds per acre onto beds drawn following fallow tillage operations, terminated after 90 to 100 days by mowing and incorporated into the soil using a multirow disk. When grown as “green manures,” a term used for plant waste, these cover crops contribute 2 to 5 tons of organic matter per acre, which improves soil health. These crops are also legumes that fix their own nitrogen from the atmosphere, which in turn can improve soil nitrogen status. It is necessary to terminate cover crops several weeks to a few months prior to planting sugarcane to allow for the organic matter to decompose because it may harm newly planted seed cane. Laboratory research demonstrated that soybean, cowpea and sunn hemp decomposed most rapidly between 77 degrees and 90 degrees Fahrenheit. In multiple field trials, sugarcane grown following soybean, cowpea or sunn hemp cover crops produced plant-cane yields that were similar or better than cane grown on land kept fallow.

Newly Planted Sugarcane

Unlike grain crops, which are often planted with minimal soil disturbance, the planting of sugarcane requires large amounts of soil to be moved to plant vegetative stalks or stalk pieces. In Louisiana, sugarcane is planted into raised beds that improve drainage. The large amount of soil disturbance associated with planting and the slow rate of establishment of newly planted sugarcane create an ideal situation for soil loss.

Sugarcane is typically planted in August through September. The goal is to simultaneously grow a winter cover crop as the newly planted sugarcane establishes. The challenge is to provide weed control for the newly planted sugarcane while maintaining cover crop growth.

Ground cover in early January of the winter cover crops Florida broadleaf mustard, cherry belle radish and Austrian winter pea, when planted in early August, averaged less than 16%, whereas ground cover for hairy vetch and Persian clover averaged more than 72% (Table 1). Biomass reduction for the mustard and radish was due to feeding from crossed-striped cabbage worms (Photo 3), whereas disease prematurely killed the Austrian winter pea.

Herbicides are applied to newly planted sugarcane to provide pre-emergent weed control; however, many of these herbicides will prevent the establishment of winter cover crops. Florida broadleaf mustard, cherry belle radish and Persian clover poorly tolerate Tricor, Command and Velossa (Table 2). Tricor caused moderate reductions to Austrian winter pea biomass. Conversely, Austrian winter pea tolerated Command, Velossa and Prowl.

To reduce the risk of herbicide injury to winter cover crops, farmers should wait a minimum of six weeks following the planting of sugarcane before planting the cover crop. Cover crops should be planted in the wheel furrow and sides of the row and not on the row top (Photo 4). Cover crops planted on the row top of newly planted sugarcane compete with and significantly reduce sugarcane yield. On-farm testing showed improved sucrose yield in sugarcane when these recommendations are followed (Table 3).

Research has documented that cover crops can be used in the sugarcane fallow period and after planting to improve soil health for Louisiana sugarcane production. Some Louisiana sugarcane producers have begun to implement these practices.

Albert J. Orgeron is a pest management specialist and associate professor in the Southeast Region; Kenneth Gravois is a professor and extension sugarcane specialist at the Sugar Research Station, St. Gabriel, Louisiana; and Paul White is a research soil scientist at the USDA-ARS Sugarcane Research Unit, Houma, Louisiana.

(This article appears in the fall 2020 issue of Louisiana Agriculture.)

Photo 1. Planting of sugarcane with a mechanical planter. Photo by Albert J. Orgeron

Photo 2. A fallow field in Assumption Parish. On the left is a conventional fallow field, and on the right sunn hemp has been planted. The sunn hemp will be shredded and incorporated into the soil one month before planting. Photo by Kenneth Gravois

Photo 3. Crossed-striped cabbage worms consume the leaves of cherry belle radish, a cover crop. Photo by Albert J. Orgeron

Photo 4. A mixture of cover crops planted on the row hips of newly planted sugarcane. Cover crops established in newly planted sugarcane fields should be planted in the wheel furrow and sides of the row and not on the row top. Photo by Albert J. Orgeron