Abstract
Measurement of plant and soil indices as well as their combinations are generally used for irrigation scheduling and water stress management of crops and horticulture. Rapid and accurate determination of irrigation time is one of the most important issues of sustainable water management in order to prevent plant water stress. The objectives of this study are to develop baselines and provide irrigation scheduling relationships during different stages of black gram growth, determine the critical limits of plant and soil indices, and also determine the relationships between plant physiology and soil indices. This study was conducted in a randomized complete block design at the four irrigation levels 50 (I1), 75 (I2), 100 (I3 or non-stress treatment) and 125 (I4) percent of crop’s water requirement with three replications in Urmia region in Iran in order to irrigation scheduling of black gram using indices such as canopy temperature (Tc), crop water stress index (CWSI), relative water content (RWC), leaf water potential (LWP), soil water (SW) and penetration resistance (Q) of soil under one-row drip irrigation. The plant irrigation scheduling was performed by using the experimental crop water stress index (CWSI) method. The upper and lower baseline equations as well as CWSI were calculated for the three treatments of I1, I2 and I3 during the plant growth period. Using the extracted baselines, the mean CWSI values for the three treatments of I1, I2 and I3 were calculated to be 0.37, 0.23 and 0.15, respectively, during the growth season. Finally, using CWSI, the necessary equations were provided to determine the irrigation schedule for the four growing stages of black gram, i.e. floral induction-flowering, pod formation, seed and pod filling and physiological maturity, as (Tc − Ta)c = 1.9498 − 0.1579(AVPD), (Tc − Ta)c = 4.4395 − 0.1585(AVPD), (Tc − Ta)c = 2.4676 − 0.0578(AVPD) and (Tc − Ta)c = 5.7532 − 0.1462(AVPD), respectively. In this study, soil and crop indices, which were measured simultaneously at maximum stress time, were used as a complementary index to remove CWSI constraints. It should be noted that in Urmia, the critical difference between the canopy temperature and air temperature (Tc − Ta), soil penetration resistance (Q), soil water (SW) and relative water content (RWC) for the whole growth period of black gram were − 0.036 °C, 10.43 MPa and 0.14 cm3 cm−3 and 0.76, respectively. Ideal point error (IPE) was also used to estimate RWC, (Tc − Ta) and LWP as well as to select the best regression model. According to the results, black gram would reduce its RWC less through reducing its transpiration and water management. Therefore, it can be used as a low-water-consuming crop. Furthermore, in light of available facilities, the farmer can use the regression equations between the obtained soil and plant indices and the critical boundaries for the irrigation scheduling of the field.
Highlights
In areas where crops are irrigated, proper management and scheduling for optimal water use is essential
The lower baseline equations fitted to the four growth stages can be used in different locations for black gram as long as the AVPD range has a wide range[42]
Examination of the lower baseline relationships showed that the coefficients a and b were different for each growth stage of the black gram
Summary
In areas where crops are irrigated, proper management and scheduling for optimal water use is essential. There are various indices for determining the crop water content and irrigation scheduling, each of which has its advantages and disadvantages as discussed by J ones[2] Some of these indices are soil-based (such as SW and soil water potential) and some are based on the crop (such as LWP, Tc, stomatal resistance, leaf color, and photosynthesis intensity). When the crop is exposed to water deficit, stomatal conductance and latent heat exchange are reduced and the cooling effect of evaporation is reduced, resulting in the plant leaves being warmer than when the crop is not stressed This property can be used to measure the crop water content after measuring the Tc of the plant[7,8]. Black gram Planting population (plants/ha) Planting date Initial emergence date 70% emergence date Transplanting date Harvest date The first weeding date Fertilization date of macro elements (N, P, K) Fertilization date of urea Spraying date of liquid Fertilizer Spraying date of amino acid fertilizer Application date of water stress
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