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Validation of Dras Model for Rice Irrigation.

Dr. M A Sattar
CSO and Head
Irrigation and Water Management Division, BRRI, Gazipur

Abstract/ Executive Summary:

Objective of the study was to compare the model predicted NIR with the BRRI recommended water application for rice cultivation and to determine rice yield by adopting model predicted NIR and BRRI recommended irrigation practices in boro season. Experiment was set-up in randomized complete block design at BRRI fame, Gazipur in Boro season 2004-05 with seven treatments and was replication thrice. The treatments were 7 in total. The DRAS model predicted relatively optimum NIR for rice cultivation in Boro/ dry season in various water regimes imposed in the field for rice cultivation. Although the model predicted slightly higher values than BRRI recommended water management practice for rice, it seems to provide irrigation water requirements for rice with sufficient accuracy for the farming community.

Keywords: Rice irrigation, Validation, DRAS model, Boro season,

Location: BRRI fame, Gazipur.

Start Date: 01-07-2004

End Date: 30-06-2005

Program Area: Crop-Soil-Water Management

Commodity: Water management

Objectives:

To compare the model predicted NIR with the BRRI recommended water application for rice cultivation.
To determine rice yield by adopting model predicted NIR and BRRI recommended irrigation practices in boro season.

Methodology:

Experiment was set-up in randomized complete block design at BRRI fame, Gazipur in Boro season 2004-05 with seven treatments and was replication thrice. The treatments were: T₁: Application of 50-70 mm irrigation water 3 days after ponded water disappeared from rice field. T₂: NIR application considering ET, S & P and RF at 0.50p. T₃: NIR application considering instantaneous ET, S & P and RF at 0.50p. T₄: NIR application same as T₂ except seepage i.e., using reported percolation only and levee protected by poly sheet. T₅: NIR application same as T₃ except seepage i.e., using reported percolation only and levee protected by poly sheet. T₆: NIR application same as T₂ but considering 0.20 allowable depletion. T₇: NIR application same as T₄ but considering 0.20 allowable depletion. BRRI dhan 29 was used as the test variety 36 days old seedling were transplanted after proper land preparation on 12 January 2005 with 20 x 20 cm spacing. Individual plot size was 3 m x 5 m having 1.0 m x 1.5 m around each experiment unit. Fertilizer was applied at the rate of 125-26-60-13-7 Kg N-P-K-Zn- S/ha. Rice yield was assessed on the basis of whole plot yield. Harvested paddy was threshed, cleaned and weighed to determine yield. Finally the yield was adjusted to 14% moisture content to determine yield per hectare. Irrigation water was applied as per model predicted NIR based on the water treatment and was measured by volumetric method. Seepage and percolation was measured by using a vertical gauge installed in the middle of experimental plot. A USWB Class A evaporation pan and a rain gauge was installed near the vicinity of the experiment field for determining rainfall and evaporation values during the growing season of rice. All the data were recorded at 7:30 AM daily to determine S & P, rainfall and evaporation from the experimental field.

Source of Information: BRRI. Proceedings of the BRRI Annual Internal Review for 2004-2005. Bangladesh Rice Research Institute (BRRI). Gazipur -1701.

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Evapotranspiration is considered the minimum amounts of water needed for optimum yield of rice. Total ET demand was 362 mm during the growth span of rice, where as S & P requirements were variable due to variable water regimes imposed for rice culture. Therefore, total water requirements for rice was varied from 709 to 887 mm depending on the variable water regimes imposed in the rice field. Total field duration of the crop was 92 days and growth duration was 128 days. Total rainfall during this period was 256 mm. rainfall mainly occurred in the later part of the growth stages of rice. The lowest amount of water applied in treatment T5, which was close to ET demand for rice during span. About 20% more water was applied in T₁ in comparison with that of ET requirements due to the presence of standing water in rice field at least a portion of the decade and it was almost similar in T₃. Water applied in other treatments was about 23-62% higher than that applied in T₁. The higher amount of water was applied in T₃ and T₆ owing to higher S & P from the rice fields. In BRRI recommended practice, irrigation water applied in almost all the decades except decade 9 and 10 due to 50 and 150 mm rainfall occurred in these decades. But application of irrigation water was needed in all decades as per model value. It was observed that NIR prediction on the basis of current year rainfall data was almost similar to BRRI recommended water management practice. It is interesting to note that irrigation water application was 16-24% less than water requirements for the treatment T₁, T₃ & T₅ having for water application. Other treatments without it required 5-10% more than actually required for optimum yield of rice. Therefore, the model predicted reasonably accurate NIR for rice in boro/dry season. Rice yield was almost similar in all the water regimes mainly due to the application of more irrigation water than the ET demand for rice. BRRI dhan29 produced about 7.5 t/ha yields irrespective of water treatments. Although rice yield did not differ significantly, about 3% yield difference was observed in T₆ and T₄ in comparison to T₁.

Knowledge Management: Report/Proceedings