Straw Incorporation-91



Home.gif (3162 bytes)

Next.gif (3180 bytes)

Back.gif (3162 bytes)

Project Leader and Principal UC Investigators

G. Stuart Pettygrove, Extension Soils Specialist, Dept. of Land, Air & Water, UC Davis

Deng Jaiyou, post graduate researcher, Dept. of Land, Air & Water, UC Davis

S. Upadhyaya, Dept. of Ag. Engineering, UC Davis

R.K. Webster, Dept. of Plant Pathology, UC Davis

C.M. Wick, UC Cooperative Extension, Butte County

J.F. Williams, UC Cooperative Extension, Sutter County

K.M. Scow, Dept. of Land, Air & Water, UC Davis

Ed Sills, Sills Farms, Pleasant Grove

Emmett and William Skinner, Durham


Many growers are experimenting with rice straw incorporation in anticipation of reduced burning over the next few years. This threeyear-old project is evaluating the role of purple vetch in rice straw management by examining how incorporating or discing in straw affects plant nutrition, disease and related topics.
UC Davis soils specialist Stuart Pettygrove (center) makes a point to growers during a field day at a Sutter County field day last summer. The scientist is examining the role of purple vetch in rice straw management.

The research centers around a relatively large, experiment (15 acres) at Sills Farms in Suffer County. A continuous rotation of vetch and rice began in the fall of 1988. Three different residue management strategies followed each rice harvest - fall burning, fall incorporation and spring incorporation. The treatments were replicated on one-acre plots.

Half of each plot is seeded with purple vetch cover crop each fall. Researchers looked at how these different cropping systems affected nitrogen nutrition requirements, vetch cultural practices, rice disease effects and soil tilth.

It appears thus far that purple vetch does not influence the breakdown of rice straw. However, straw decomposition studies are still in progress.

Measurements show a decrease in resistance to tillage tools where straw is incorporated rather than burned, but more study is needed to determine whether this indication of improved soil filth is due to higher water content on incorporated plots than on burned plots.

Researchers have also confirmed that growing even a modest amount of vetch adds considerable nitrogen to the rice crop. In both 1990 and 1991 significant rapid vetch-growth did not occur until April, so growers interested in using this technique should be careful not to incorporate vetch prematurely.

Vetch was especially effective in replacing fertilizer nitrogen where straw was either burned or incorporated in the fall, providing an apparent fertilizer nitrogen replacement value of 70 to 105 pounds nitrogen per acre. Compared to the burned plots, those plots with straw incorporated in the spring also appeared to need slightly more nitrogen to reach maximum yield. Vetch did not moderate this increase.

In 1991 researchers observed that rice grain yield on the fall-incorporated, green-manured plots was considerably higher than maximum yields on burned plots. Only a very small difference in nitrogen-response was observed on no-vetch plots.

Researchers also report significant progress on one of their other objectives diagnostic tools to measure nitrogen.

One of these tools is an anaerobic incubation ammonium soil test, which is used to estimate mineralizable nitrogen in the soil. However, further work is needed to develop this test.

The other tool is a chlorophyll meter to determine nitrogen levels in rice leaves.

Stem rot and aggregate sheath blight were present in many research plots at a low level in 1991. No straw management or vetch effects were seen, except possibly that aggregate sheath spot is more prevalent at the higher nitrogen rates on the green-manured plots.

Purple vetch also did not respond to applied superphosphate fertilizer or rock phosphate pelleting of vetch seed. Lime and phosphorous studies are continuing.


Home.gif (3162 bytes)Next.gif (3180 bytes)Back.gif (3162 bytes)