Bafra Valley (Turkey)

Bafra Valley (Turkey)

Context
The Bafra Valley includes a total irrigated surface area of 21.550 ha located in the north of Turkey (Figure 1). The Bafra Valley is composed by two different zones which are Bafra Plain Right Land Irrigated Area with 11550 ha and Bafra Plain left Land Irrigated Area with 10.000 ha devoted to rice. At the Bafra Plain, irrigations are organızed by two irrigation association of 7rd Regional Directorate of General Directorate of State Hydraulıc Works. An annual average of approximately 24 million m3 of water is used to grow maize, rice, forage, and horticultural crops (7rd Regional Directorate of The General Directorate of State Hydraulic Works).

The climate of the Bafra Valley is temperate; summers are cool and winters are warm and rainy. The majority of the precipitation falls in autumn and winter. In the Bafra Valley, the highest temperature is observed in July (38.4 oC) and the lowest temperature is observed in February (-7.9 oC). Average relative humidity is about 75.5%. The total annual precipitation is about 794.2 mm. The average annual rainfall is about 222 mm during the rice sowing season (from May to October). The ombrothermic diagram (Figure 2) shows the variation in the average temperature and precipitation for the Bafra district during the year. According to the diagram, it can be seen that there is a dry period in Bafra district between May and September and the precipitations is concentrated in the period between October and December.

 In Bafra Valley, the soil texture is generally clayey. Coarse textured soils are mostly located on the right coast of the plain. Most of the soils are transported soils and the alluvial soils dominate. The slope in the plain is in the range of 0-2 m. The elevation is generally between 0-2 m and 10-20 m.

The main water source is the Kızılırmak River, regulated by the Derbent and the Altınkaya dams. The water uptake is a weir in the Kızılırmak river that diverts water to the main irrigation canal. The distribution network is ramified, with 5 secondary canals and many smaller tertiary canals. The Bafra Plain Left Side Irrigated Area has three main drainage channels that dump the water to the sea.
The most common rice irrigation technique in the Bafra Valley is wet seeding and continuous flooding. In particular, after the initial flooding, wet seeding is carried out mechanically by centrifugal spread, and before pesticide or herbicide treatments, the fields are drained; then the fields are kept flooded up to two or three weeks before harvesting.

Problems and difficulties
1. The excessive use of groundwater in the Bafra plain, especially in the areas close to the sea: an increase in water demand has been observed in recent years due to the extension of rice-growing areas in the plain, as a result, the sea water invaded the aquifer. In particular, the EC and SAR values of groundwater have significantly increased due to the intrusion of seawater into the aquifers, reaching levels that are not beneficial for crops.
2. The increase of soil salinity: the main water source of Bafra Valley is Kızılırmak River, which is one of the saltiest water resources in Turkey, its EC value is about 2 dSm-1 and it belongs to the water class C3S1. Therefore, due to the use of salt water from Kızılırmak River in rice cultivation, soil salinity has increased in Bafra Valley. Furthermore, due to the shallow groundwater depth and the absence of a drainage system in some areas of the region, the salt accumulated in the paddy rice cannot be washed away.
3. The irrigation distribution network is not extensive enough in the region to irrigate the entire paddy growing areas in the Bafra plain, thus, the rice farmers use groundwater or drained water to irrigate their paddy fields.

Objectives
The aim of this study is to investigate the effects of new water-saving irrigation technologies and applications on rice yield and yield components, water productivity and greenhouse gas emissions, as an alternative solution to be adopted instead of the traditional irrigation practices in the Bafra rice.

Experimental sites
The experimentation was conducted at the pilot farm of the Black Sea Agricultural Research Institute located in Bafra Valley of Samsun province during the rice-growing season in 2019 and 2021 (June-October). A total of 36 plots (5×5 m2) were established in the pilot farm with a randomized complete block design combining two rice varieties of rice (Osmancık-97 and Rekor CL) and six irrigation treatments with three replicates: 1) WFL/DFL: water transplanted/dry seeding and immediate flooding; 2) AWD(-5): water transplanted/dry seeding and immediate flooding and alternate wetting and drying (water tube threshold level at which the flooding condition was restored in the plot equal to -5 cm below the soil surface); 3) AWD(-10): water transplanted/dry seeding and immediate flooding and alternate wetting and drying (water tube threshold equal to -10 cm below the soil surface); 4) AWD(-15): water transplanted/dry seeding and immediate flooding and alternate wetting and drying (water tube threshold equal to -15 cm below the soil surface); 5) Drip irrigation 1.75 x pan evaporation (Epan); 6) Drip irrigation 2.0 x pan evaporation (Epan). Measured data include irrigation water inflow and outflow, water productivity, greenhouse gas emissions ( CH4 and N2O), field water depth, soil moisture, and yield production.