Ronnie Levy and Manoch Kongchum

For rice farmers in Louisiana, determining the best tillage methods and water management practices is key to achieving higher yields. Here reduced tillage methods include no-till and stale seedbed preparation. True no-till options include planting into existing crop residue, planting into a fallow field or planting into crawfish ponds with no seedbed preparation. Stale or minimum tillage seedbeds are prepared in the fall and then left undisturbed until planting. In Louisiana even a seedbed prepared in early winter can be covered by native vegetation by planting time. Land prepared in the fall remains bare for only a short period of time before annual bluegrass and other cool-season species emerge, appearing as a planted cover crop.

Interest in reduced tillage rice production began in the late 1980s at a time when the predominant method of seeding in south Louisiana was water seeding into flooded fields. The driving force behind this preference was red rice. This weedy form of rice belongs to the same genus and species of cultivated rice. Herbicides that killed red rice also killed cultivated rice. Water seeding helped suppress red rice and is the most effective cultural control method available, destroying any rice that had emerged prior to planting and preparing a seedbed for planting. Rice farmers used equipment called a water level to bury existing vegetation and allow soil to settle flat.

In other crops, planter manufacturers were modifying existing equipment or designing entirely new planters to meet the challenges of good seed placement in no-till or reduced tillage seed beds. Because none of these planters work in water seeded situations, one of the most difficult challenges to reduced tillage rice production was establishing good seed-to-soil contact.

Early attempts were met with frustration and disappointment. Only the most determined producers adopted reduced tillage methods for rice while acreage devoted to reduced tillage in other crops took off. In northeast Louisiana, where drill-seeding was already in practice, they quickly adapted drill-seeding for rice and had very few red rice problems.

In 2002 a technology called Clearfield was introduced to commercial rice production. This nongenetically modified trait incorporated herbicide tolerance into the cultivated rice. It provided growers with the ability to control red rice with herbicides, which meant they would no longer have to use water seeding. Drill seeding and broadcast seeding followed this introduction, which also opened the door to no-till and reduced tillage rice production. Without Clearfield rice varieties, it is unlikely that dry seeding would have ever increased significantly. New herbicide technology continues to increase no-till and reduced tillage production acres in rice production in Louisiana.

Another driving factor was to reduce sediment loss from rice fields from working the fields in the water and draining sediment rich soils in nearby waterways. Research showed that losses could be reduced from fields by reducing the type of field preparation and when they were performed.

All forms of reduced tillage acreage increased as the adoption of Clearfield technology progressed. In 1998 only 4% of Louisiana’s rice acreage was in true no-till production, with a total of all reduced tillage forms adding up to 17%. The introduction of Clearfield rice in 2002 resulted in a dramatic increase in reduced tillage acreage to nearly 30%. The acres devoted to reduced tillage are influenced by weather, especially for those who prefer a fall stale seedbed, so some fluctuation in acreage has occurred. Overall, the adoption of reduced tillage practices has shown a steady increase to the 2022 level of almost 49.3% of rice being planted in this manner.

In the beginning, reduced tillage systems were used by producers that promoted soil conservation practices. It was considered risky and difficult. Today reduced tillage is a common practice being utilized by nearly all rice farmers to some degree. Reduced tillage is gradually gaining acceptance as better equipment and cultural practices are perfected. This trend is expected to continue well into the future.

Another concern for the continued sustainability of rice production has been control of the amount of greenhouse gases emitted during rice cultivation. Research to develop better management practices to reduce these emissions is continuing. Implementation of water management practices to reduce greenhouse gas emissions has been shown to be feasible in irrigated rice production. Methane and nitrous oxide emissions from alternate wetting and drying have been evaluated in various rice production systems. Three consecutive years of research on the effects of water management practices in rice cultivation on methane and nitrous oxide emissions have been conducted at the AgCenter’s H. Rouse Caffey Rice Research Station near Crowley, Louisiana.

The research compared methane and nitrous oxide emissions from four water management practices: delayed flooding; alternate wetting and drying; furrow irrigated, which is also known as a row rice system; and semiaerobic water management. In a delayed flood, drill-seeded system the permanent flood is applied three to four weeks after planting or at four- to five-leaf growth stage. The water level was maintained throughout the season until two to three weeks before harvesting. This management system was used as a baseline practice for the other three water management systems. For example, in the alternate wetting and drying, planting method and permanent flood timing were similar to delayed flood, but the water level was maintained lower to let it dry out naturally in midseason before re-flooding. In a semiaerobic and furrow irrigated rice system, no flood water is maintained on the soil surface. The only difference in these two systems was furrows were pulled to aid in watering. Irrigation water was applied as needed.

Methane and nitrous oxide emissions were observed from 2018 to 2020 using various water management systems. The findings showed:

The delayed flooding system consistently produced the highest methane emissions, which was approximately three times higher than other water management systems. In contrast, this system consistently produced the lowest levels of nitrous oxide emissions among the different water management practices.

Furrow irrigated rice, or row rice, and semiaerobic systems produced higher levels of nitrous oxide emissions each season while maintaining lower levels of methane emissions.

The AgCenter’s research showed that the total global warming potential from these two greenhouse gases was higher in the delayed flooding than the other water management practices (Figure 1).

Yield performance was also investigated in this study. The highest yield was observed in the delayed flooding system (Figure 2). It was significantly higher than the rice with furrow irrigation and semiaerobic systems, but it was not different from the alternate wetting and drying water management practices.

Research and extension programs will continue to look at ways to increase rice production and maintain rice sustainability while keeping rice production environmentally friendly.

Ronnie Levy is the state rice specialist for the AgCenter. He is stationed at the H. Rouse Caffey Rice Research Station in Crowley.

This article appears in the winter 2023 edition of Louisiana Agriculture.

Research and extension programs will continue to look at ways to increase rice production and maintain rice sustainability while keeping rice production environmentally friendly.

Water leveling the field before planting rice is used to destroy red rice and level the planting field but increases erosion. LSU AgCenter file photo

One of the many benefits of reduced tillage in rice fields is the reduction in sediment loss. Water leaving the reduced tillage rice field at right carries away far less sediment than the water leaving the field shown at the left after tillage. LSU AgCenter file photos