Document Type : Research Article
Author
Department of Water Engineering, Faculty of Agriculture and Natural Resources, Imam Khomeini International University, Qazvin, Iran
10.22067/jsw.2024.85046.1350
Abstract
Introduction:
Salinity stress causes the reduction of crop evapotranspiration (ETc) and yield. Unsuitable seed planting date causes negative effects of atmosphere (such as temperature stress and ...) in crop growth period. So that the salinity stress and unfavorable climatic conditions (in crop growth period) have an interaction effect on the reduction of crop water uptake. The mentioned conditions effect, should be investigated on crop transpiration amount (actual water requirement) and soil surface evaporation losses. This research results will have a determinative effect on the optimal use of water resources.
Materials and Methods:
The studied crop in this research was S.C 704 maize. Crop planting place was the mini-lysimeter with diameter of 40 cm and height of 70 cm. Experiment factors were included of soil salinity stress and seed planting date. Soil salinity treatments were selected at four levels of 1.7(S1), 2.5(S2), 3.8(S3), 5.9(S4) dS.m-1. Seed planting date included of 5 May (P1), 25 May (P2) 14 June (P3) and 4 July (P4). Crop growth period for all planting date treatments, was 140 days (FAO-56). Experiment was conducted as factorial and in a completely randomized design, with 16 treatments and three repetitions. Variance analysis and average comparison of data, was done by SPSS software and with Duncan's multi-range test (at 5% probability level). Daily soil moisture amount was measured by a moisture meter. Irrigation time was determined for without water stress conditions. Therefore, readily available water limit was determined 0.4. Irrigation volume was calculated according to soil moisture deficit (up to FC limit), soil density, root depth, leaching fraction and soil surface area. To separate the evapotranspiration components, all treatments were performed in two series of mini-lysimeters. In first series, soil moisture reduction was related to crop evapotranspiration amount. But in second series, the plastic mulch was placed on soil surface. Soil moisture reduction in the second series, was only related to crop transpiration amount. Difference of data in the first and second series, was equal to the evaporation amount. Linear function of Mass and Hoffman (1977) was used as the function of; evapotranspiration-salinity, transpiration-salinity and evaporation-salinity.
Results and Discussion:
By salinity increasing from S1 to S4 level and in dates of; P1, P2, P3 and P4, evapotranspiration amount was measured in range of; 619-548, 621-549, 624-547 and 625-544 mm, transpiration amount was measured in range of; 429-309, 421-295, 418-281 and 412-265 mm and evaporation amount was measured in range of; 190-239, 200-254, 206-266 and 213-279 mm, respectively. In salinity stress effect, soil water potential, water uptake and crop transpiration was decreased. By crop water uptake reduction, the remained water in soil was used for evaporation. In S4 level and on dates of; P1, P2, P3 and P4, crop transpiration portion was decreased to 12.9%, 14.1%, 15.6% and 17.2%, respectively, and evaporation portion was increased to the same amount. By changing of seed planting date (for optimal use of moderation atmospheric conditions, during the crop growth stages), is prevented the increasing of evaporation portion. In initial stage of growth period, only 0 to 10% of soil surface is covered by crops (FAO-56). For this reason (in the crop initial growth stage), the evaporation component has a dominant portion in the crop evapotranspiration parameter. As a result, placing of initial growth stage in warm days of year, was caused an increasing in evaporation losses. Therefore, S1P1 treatment was the optimal condition for transpiration increasing and evaporation decreasing. The estimated functions showed that (in salinity stress conditions) crop transpiration decreased more than ETc. Therefore, transpiration rate should be considered as the crop net water requirement, instead of ETc. Mass-Hoffman function showed that in stress condition, the decreasing slope of transpiration and evapotranspiration and the increasing slope of evaporation, became more. So that in planting dates of P1, P2, P3 and P4, for 1 dS.m-1 increasing in soil salinity, the evapotranspiration rates were decreased to 2.51%, 2.82%, 3.3% and 3.65%, respectively, and the transpiration rates were decreased to 6.1%, 7.34%, 8.42% and 9.2%, respectively, and the evaporation rates were increased to 5.5%, 6.7%, 7% and 7.82%, respectively.
Conclusions:
Salinity and atmospheric temperature stresses had interaction effects on evapotranspiration and components rates. Postponing of seed planting date and not using of optimal weather conditions (in spring), were caused the transpiration damaging (favorable part) and evaporation increasing (unfavorable part). Therefore, in irrigated crops, the planting seeds process should not be done in the warm months of year (especially in July and August). As a result, by controlling the soil salinity and choosing the appropriate date for planting seeds, water is used optimally.
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