Effects of Supplementary Irrigation and some Stress Modifiers (Vermicompost, Nano Iron Oxide, and Humic Acid) on Grain Filling Components, Nodulation and Grain Yield of Chickpea (Cicer arietinum L.) under Rainfed Conditions

IntroductionChickpea (Cicer arietinum L.) is an important pulse crop that also serves as a soil enhancer. Among the abiotic stresses, water deficit under rain-fed conditions limits crop production. In this regard, stress modifiers application (such as humic acid, nano iron oxide, and vermicompost) can decrease the effects of water deficit under rain-fed conditions and increase grain filling components, relative water content and quantum yield of plants. Iron (Fe) is an essential element in crop plants. Application of iron and humic acid alleviates drought effects due to enhancement in chlorophyll content, relative water content and nodulation in chickpea plants under stress. The aim of this study was to evaluate the effects of supplementary irrigation and stress modifiers (such as humic acid, nano iron oxide and vermicompost) on nodulation and yield of chickpeas under rain fed conditions.Materials and MethodsA factorial experiment was performed at a farm near Ardabil city in 2023 using a RCBD with three replications. Experimental treatments were vermicompost (without application as control, application of 4 and 8 ton.ha-1), irrigation at two levels (rainfed as control and supplementary irrigation at the flowering stage) and application of humic acid and nano iron oxide (no application as control, application of humic acid, nano iron oxide, humic acid and nano iron oxide foliar application). The chickpea cultivar ‘Adel’ was planted with the optimal density of 35 seeds.m-2. Vermicompost was prepared by Gilda Corporation and nano iron oxide from Pishgaman Nanomaterials Company. Application of nano iron oxide and humic acid was in two growth stages (vegetative growth and before flowering). In order to study the nodulation, three pots (with a diameter of 45 and depth of 60 cm) were sown in each plot before planting. The pots were removed at flowering and after washing, some traits like the number of inactive and active nodules were recorded. To investigate grain filling components, the first sampling was taken 14 days after podding and other samplings were taken in 5-days intervals to determine the accumulation of grain weight. The protein amount was calculated by multiplying the nitrogen content by 6.25. For the determination of grain yield, 0.5 m2 were harvested in each plot.Results and DiscussionThe results showed that chlorophyll index, relative water content, quantum yield and number of pod per plant were significantly affected by the main effects of irrigation levels, vermicompost and humic acid. Also, irrigation levels×vermicompost×humic acid interactions had a significant effect on grain filling components (grain filling period; grain filling rate; effective grain filling period; maximum of grain weight) and grain yield. The results indicated that water deficit under rainfed conditions compared to supplementary irrigation at flowering stage led to a significant decrease in chickpea yield and yield components. However application of stress modulators (vermicompost, nano iron oxide and humic acid) and supplementary irrigation at flowering stage moderated the adverse effects of stress. Modulating effects of studied vermicompost, nano iron oxide and humic acid were emerged by physiological traits improvement‎ (SPAD, quantum yield, grain filling components, number of active nodules  and  nodule dry weigh, and improvement of the water status (relative water content). The use of supplementary irrigation and stress modifiers (vermicompost, nano iron oxide and humic acid) increased grain filling rate (51.96%), grain filling period (62.5%) and effective grain filling period (44.61%) in compared to the no application of stress modifiers under rainfed condition. Application of vermicompost with nano iron oxide and humic acid increased number of active nodules (2.8 fold), nodule dry weigh (45%) and percentage of active nodules (2.3 fold) in compared to control (no application of stress modulators). Also, the application of stress modulators and supplementary irrigation at flowering stage had the highest efficiency in improving grain yield and led to 57% increase in grain yield compared to the no application of theirs under rain fed conditions.ConclusionBased on the results of this study, applying supplementary irrigation at flowering along with stress modifiers can enhance nodulation, grain filling components, and grain yield of chickpea under rainfed conditions.