Information from 2000 Missouri Rice Research Update, February 2001.

Flood Termination on Water-seeded Rice

Gene Stevens, Alan Sheckell, Chris Moylan, Holly Wilson, Keith Birmingham

Abstract

The objective of this test is to determine when the optimal time is to take the flood off of water seeded rice. This study was conducted at the University of Missouri Lee Farm at Portageville. Drew, Cypress, and Cocodrie were tested on zero-grade pans. Yields were reduced significantly in each variety when the flood was drained before the soft dough stage (at least one yellow hull). Yields and milling properties were also reduced when harvest was delayed until grain moisture decreased to 9.5% (October 25) as compared to 22% (September 18).

Introduction

In 1999, approximately 40% of the Missouri rice farmers used the DD-50 program. This program is used to improve timeliness of rice management decisions by utilizing temperature data from the Commercial Agriculture weather station network.

We have been able to do a good job of calibrating model to the growth stages of each of the major rice varieties grown on drill seeded rice by using field data at the Missouri Rice Farm. However, we do not have a good database for making recommendations on when to terminate flood irrigation on rice. This is important because it effects rice yield, milling properties and timeliness of harvest.

Materials and Methods

In the fall of 1999, a 10-acre field of Sharkey clay soil at the University of Missouri Lee Farm was put to zero-grade. Permanent levees were constructed around the field. At two locations in the field, we installed pipes and gates to control the water depth in the field. A cross leeve was built to make a smaller field for conducting a flood termination experiment. Twelve rice pans (120 feet X 40 feet) were constructed in this area. A system of drain pipes with separate controls were placed in each individual pan. These pipes were made to control flood depth and to allow complete drainage into a main ditch. This main ditch was connected to an exit pipe at one end of the field.

A permanent flood was established in all of the pans. Drew, Cypress and Cocodrie rice seeds were soaked in sacks for 24 hours and drained for 12 hours. Each pan was divided into three equal size subplots. Varieties were water-seeded into subplots.

Pre-germinated seeds were broadcast by hand on May, 15 2000. There were four flood termination treatments with three different varieties. The flood was taken off at different growth stages. The target growth stages for draining the pans were 50% heading, soft dough (1 grain yellow), ˝ straw hulls, and all brown hulls. These growth stages were based on Drew while the Cocodrie matured earlier and Cypress matured later. The Cypress and Cocodrie received 90 lb N per acre of urea applied 30 days after seeding. The Drew had 75 lb N per acre applied at the same time. All the varieties had one 60 lb N per acre midseason application applied with an airplane. There were two harvest dates to see how the milling would be effected after the flood had been taken off the rice.

Results

Rice yields were reduced when pans were drained before the soft dough stage (at least one yellow hull). The table in the next column shows the rainfall that occurred when rice was maturing. Yields decreased between the first and the second harvest. The average moisture content of the grain at the first harvest (Sept. 18) was 22%. The pans that were drained at 50% heading averaged 18% moisture. The yield reduction was due to shattering, lodging, and bird damage. The average grain moisture content of the second harvest was 9.5% (October 25). There were more broken grains (% head) in samples from this date.

Date	Rainfall, in.
Aug 18	0.19
Aug 20	0.12
Aug 24	0.78
Aug 25	0.42
Sep 8	0.03
Sep 11	0.37
Sep 12	0.14
Sep 14	0.04
Total	2.09

Conclusion

The first year results showed that the 50% heading stage is too early to terminate the flood. All varieties had good high yields in the soft dough stage. The best time to terminate the flood may be between soft dough and ˝ straw hull stage.

Table 1. Effect of flood termination on water seed rice yields.

Trt	Flood Drained	Description at Flood Termination	Variety	Milling				Yield Bu/Acre
				Harvested Sept. 18		Harvested Oct. 25		Harvest Sept. 18 Bu/a	Harvest Oct. 25 Bu/a
				Head %	Total %	Head %	Total %	Harvest Sept. 18 Bu/a	Harvest Oct. 25 Bu/a
1	Aug. 17	50% Heading	Drew	62	70	59	71	153	125
		20% Heading	Cypress	62	69	56	69	129	107
		80% Heading	Cocodrie	65	70	57	70	160	110
2	Aug. 28	Soft Dough	Drew	60	69	52	70	183	133
		Soft Dough	Cypress	64	70	59	70	155	137
		˝ Straw hull	Cocodrie	61	68	57	71	182	146
3	Sept. 5	˝ Straw hull	Drew	58	67	49	70	178	159
		Ľ Straw hull	Cypress	61	69	58	71	160	140
		˝ Brown hull	Cocodrie	63	69	60	71	177	146
4	Sept. 14	All Brown hull	Drew	61	69	53	71	179	176
		All Brown hull	Cypress	63	69	62	71	159	138
		All Brown hull	Cocodrie	63	69	61	72	184	149

Cocodrie matured earliest and Cypress matured last.
Each plot is 1/10 of an acre. Soft dough stage had at least one yellow grain hull.

This experiment funded by a USDA Irrigation Grant.

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