Agroecosystems Lab

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Managing nitrogen in alternative rice establishment and weed control systems


Kaden Koffler, Bruce Linquist, Luis Felipe Tiene Da Silva, Jim Hill, Cass Mutters, Chris Greer, and Chris van Kessel
Department of Plant Sciences, University of California, Davis

Photo of data logger California rice farmers are facing major weed management challenges due to the development of herbicide resistance in certain weeds. This has prompted the exploration of alternative rice establishment systems geared toward facilitating the use of more effective broad-spectrum herbicides in the early season, such as Roundup. Such systems involve "flash-flooding" to germinate weed seeds, and then a quick draining of the field, followed by a broad-spectrum herbicide application. Once the weeds are killed by the herbicide, the field is either permanently flooded for aerial rice seeding into water, or the rice is drill-seeded. In the case of drill-seeding, another "flash-flood" is performed to germinate the rice seed, followed by another draining of the field until the rice is rooted and established, after which a permanent flood is finally brought on. In some systems, no tillage is performed in the spring. Depending on the particular features of the system, the field can be flooded and drained up to 3-4 times in the early season before a permanent flood is established. This wetting and drying of rice fields makes efficient nitrogen (N) management extremely difficult because both the N applied as ammonium fertilizer and native soil N can be nitrified during dry-downs, and then lost through denitrification after the field is reflooded.

Photo of Luis in field Photo of Nitrogen trials
To minimize N losses in these alternative systems, both the timing and method of N fertilizer application, and the quantity of N applied need to be optimized for each individual system (See Table 1 for system descriptions). We are evaluating rice growth, yield, and N uptake, and soil mineral N dynamics, with N application rates ranging from 0 - 200 lb N / acre, in all of the rice establishment systems in the study. In addition, we are continuously measuring soil moisture with data loggers in select systems to link changes in soil moisture to changes in soil mineral N.


Table 1. Features of the different rice establishment systems being studied.
System
Tillage
Flash Flood fo
Weed Seed Germination
Water Seeding
Drill Seeding
Flash Flood for
Rice Seed Germination
1
Conventional
x
2
Conventional
x
x
3
Conventional
x
x
4
No Spring Tillage
x
x
5
No Spring Tillage
x
x
x