The field experiments were conducted at the research field of IWM Division, BARI, Gazipur and ARS, BARI, Rajbari, Dinajpur during the rabi (dry) seasons of 2014-2015 and 2015-2016. The soil was silt loam with an average field capacity (FC) of 28% and mean bulk density, 1.5 g/cc at the research field of IWM, Gazipur and clay loam with an average FC of 30% and mean bulk density, 1.44 g/cc at the research field of ARS, Dinajpur.
Determination of soil chemical properties: Before maize sowing, soil samples were randomly collected from the desired depth of the experimental plots. The percentage of organic matter (OM), pH, total nitrogen (N), phosphorous (P), potassium (K), sulpher (S), zinc (Zn) and Boron (B) were determined in the Soil Science Laboratory, BARI, Gazipur and Regional Soil Test Laboratory, SRDI, Dinajpur. The results of the selected soil properties of the experimental plots.
Treatments and irrigation methods: The field experimental plan yielded nine treatments (3×3) each replicated thrice in a split-plot in randomized complete block design producing a total of twenty-seven plots. The layout of the split-plot design involved three irrigation levels (I1, I2, and I3) in the main plot and three methods (M1, M2, and M3) subplot treatment in three replications. The irrigation treatments were as follows:
Three irrigation levels (main plot treatment):
- I1:Irrigation water applied to 100% FC
- I2:Irrigation water applied to 80% FC
- I3:Irrigation water applied to 60% FC
Three irrigation methods (subplot treatment):
- M1: Alternate wetting and drying furrow irrigation (AWDFI)
- M2: Fixed wetting and drying furrow irrigation (FWDFI)
- M3: Traditional furrow irrigation (TFI)
AWDFI indicates that water is to be applied to alternate furrows. For example, during first irrigation, furrows 1, 3, 5 …….to be irrigated keeping 2, 4, 6, ……. dry but during second irrigation, the furrows 2, 4, 6, ……. to be irrigated and 1, 3, 5, ….to be kept dry and so on. FWDFI means that irrigation application was kept fixed to certain furrows keeping two adjacent furrows dry and the same sequence continues from first to last irrigation. This indicates that the irrigated furrows will receive irrigation every time but the non-irrigated furrows will never receive any irrigation. TFI indicates that all furrows are to be irrigated at every irrigation. It means that irrigation water was applied on both sides of the root system for each irrigation.
Irrigation water was applied at different growth stages of maize-based on the soil moisture content of the furrows. Total four irrigations were applied to all the treatments during different growth stages of maize. The selected growth stages received irrigation are: initial growth (25-30 DAS), tasselling (55-60 DAS), silking (85-90 DAS) and grain filling (110-115 DAS) stages of maize which also followed by plant and soil moisture observation method depending on rainfall or soil moisture. Soil moisture before each irrigation was monitored. Gravimetric soil water content was determined before each irrigation event. The soil samples were collected considering a root zone depth of 45 cm (initial stage), 60 cm (tasseling stage), and 75 cm (silking and grain filling stages). The soil was sampled in 15cm increments, well-mixed, subsampled, weighed, dried at 105oC, and reweighed to determine gravimetric moisture content. The irrigation water requirement was calculated by the formula (Mandal and Dutta,1995; Michael, 1978; Majumdar, 2004): Crop dry matter (DM) was measured at different intervals during the crop growing seasons from every replication In 2014-2015, dry matter of roots was not recorded and only shoot dry matter was recorded. But in 2015-2016, the biomass of roots and shoots was collected. The roots were collected to a depth of 20 cm from the sampling area of 20 cm x 20 cm. The roots were cleaned and washed with clean water. Plant biomass was dried at 600 C until it reached a constant weight by the oven-dry method. No dry matter has been shown in this report for ARS, BARI, Dinajpur. Data on yield contributing characters, dry matter, and water productivity were statically analyzed to test the effect of irrigation levels and methods on these parameters by the analysis of variance using R-Foundation for Statistical Computing Platform (R version 3.1.2: 2014-10-13). All the treatment means were compared for significant differences at a 5% probability level of significance (P≤0.05).