Effect of Water Regimes on the Growth of and Yield of Rabi / Summer Groundnut Genotypes in Northern Transition Zone of Karnataka

A field experiment was conducted during rabi / summer (December to April) 2016-17at AICRP on groundnut UAS, Dharwad located at 15°26' North latitude, 75°07' East longitude and at an altitude of 678 m above mean sea level (MSL). It lies under the Northern Transition Zone (Zone-8; NTZ) of agro-climatic zones of Karnataka on medium deep black soil. The experiment was laid out in split plot design with three replications involving four water regimes viz. I₁: Control : i.e., seven irrigations at 15 days interval from sowing to 105 days after sowing (DAS), I₂: Stress at pegging stage by withdrawal of one irrigation at 45-60 DAS, I₃: Stress at pegging and pod filling stage with withdrawal of 2 irrigations at 45-75 DAS, I₄: Stress at pegging, pod filling and kernel development stage i.e., withdrawal of 4 irrigations from 45-105 DAS as main plots and four genotypes as sub plots viz.G1: Dh-86, G2: Dh-101, G3: K-9 and G4: G2-52. The soil of the experimental site was medium black clay with pH (7.43), EC (0.21dS m^-1), organic carbon content was (0.56%), available N (249 kg ha^-1), P₂O₅ (23 kg ha^-1) and K₂O (359 kg ha^-1). The mean monthly rainfall from September to April for the past 66 years at the Main Agricultural Research Station, Dharwad was 351.4 mm whereas the rainfall received during September-April 2016 was 127.4, which is much lower than long-term average. The crop was sown on December 28^th 2006 and the temperatures during the crop growing season (January to April), mean maximum temperature for January, February and March were 4.4, 1.8, 0.6 and 0.0°C higher than long term average. Whereas mean minimum temperature was 1.5 and 1.0 higher during January and February but 3.7 and 0.5°C lower during March and April, respectively, compared to long term mean monthly averages (1950 to 2015).
       
Bold and healthy groundnut seeds were hand dibbled and covered with soil. At the time of sowing surface irrigation (flooding), subsequently sprinkler irrigation at 15 days intervals was followed as per the treatment. The height was measured at harvest in centimeters from the base to the tip of the plant. Leaf area was measured by disc method as suggested by Vivekanandan et al. (1972) and it was calculated by using formula:        
Leaf area index was calculated by dividing leaf area plant^-1 by the land area occupied by a single plant. Pods were dried completely (up to 8% moisture level) and weighed. On the basis of pod yield of net plot^-1 the pod yield ha^-1 was calculated and expressed in kg ha^-1. The analysis and interpretation of data were studied using the Fischer’s method of analysis of variance technique as described by Gomez and Gomez (1984).

Growth parameters of groundnut are significantly influenced by different water regimes and genotype. Among the different water regimes, stress at pegging stage (I₂) recorded significantly higher pod yield and haulm yield (2,858 kg ha^-1 4,648 kg ha^-1, respectively). However, it was on par with (I₁ water regime) no moisture stress crop (2,870 kg ha^-1 and 4691 kg ha^-1, respectively) (Table 3). Withholding of two irrigations at pegging and pod development stage (I₃) and withholding of irrigation at pegging, pod filling and kernel development stage (I₄), drastically reduced pod yield to the extent of 32.04% (1,950 kg ha^-1) and 70.64% (842 kg ha^-1) respectively, over no moisture stress (I₁)  (Table 3). It might be due to inadequate availability soil moisture at reproductive stages, like pod filling and kernel development stages, two critical stages of crop which will hinder the translocation of photosynthates from leaves to fruiting parts and pod affecting the pod formation and pod yield.
       
The higher pod yield and haulm yield in I₂ was due to better performance of growth attributes. I₁ (Control, 7 irrigations at 15 days interval from sowing to 105 DAS) recorded significantly higher plant height, leaf area, leaf area index, number of branches plant^-1, dry matter in stem, dry matter in leaves and total dry matter production at harvest (22.3 cm, 11.76 dm² plant^-1, 3.92, 7.52, 15.66 g, 8.06 g and 33.87 g, respectively) as compared to other water regimes (Table 1, 2 and 3). However, it was found on par with the treatment of I₂ (Stress at pegging stage: withdrawal of one irrigation between 45-60 DAS). Higher leaf area and leaf area index (Table 1) exposed higher surface area for assimilation of photosynthetic ability and  higher  dry matter production plant^-1 (Vaghasia, 2010).
 

 

 

       
Moisture stress at pod filling and kernel development stage brings premature closer of stomata to reduce water loss, but also decrease carbon dioxide diffusion in to leaves, thereby affecting the photosynthesis (Asanaand Sani, 1985). Moisture stress also causes dehydration of protoplasm causing reduction in photosynthetic rate which ultimately reduces plant height, leaf area, leaf area index, number of branches plant^-1, dry matter in stem, dry matter in leaves and dry matter in pods at harvest in I₃ (Stress at pegging and pod filling stage i.e., withdrawal of 2 irrigations at 45-75 DAS and I₄ (Stress at pegging, pod filling and kernel development stage i.e., withdrawal of 4 irrigations between 45-105 DAS). Peanut yield is influenced by the availability of soil moisture during vegetative and reproductive stages and crop experiencing drought during the reproductive phase shows significant yield reductions (Singh, 2011).
               
Efficient utilization of the physiological traits for improving drought resistance in a groundnut requires anunderstanding of the inheritance and genetic relationships of the traits that are available for selection of genotypes, which is needed to identify the heritability of physiological traits related to drought resistance under different drought conditions (Cruickshank et al., 2004, Williams, 1998, Nigam et al., 2005). Groundnut yield differed significantly among the genotypes. The genotype Dh-86 (2,376 kg ha^-1) recorded significantly superior pod yield over other genotypes viz., Dh-101 (2,215 kg ha^-1), K-9 (2,048 kg ha^-1) and G2-52 (1,880kg ha^-1). The yield of Dh-86 was more to the extent of 6.8, 13.8 and 20.8 per cent, respectively, compared to Dh-101, K-9 and G2-52. With Dh-86 Increase in the pod yield (2,376 kg ha^-1) and haulm yield (3,816 kg ha^-1) was due to higher growth parameters observed during the cropping period.
       
At harvest, significantly taller plant height (19.4 cm), higher leaf area (11.55 dm² plant^-1), leaf area index (3.85), number of branches plant^-1 (7.46), dry matter in stem (15.30 g plant^-1), leaves (7.79 g plant^-1) and total dry matter production (32.10 g plant^-1) was observed in the genotype Dh-86 compared to other genotypes mainly due to difference in their genetic makeup of the genotype (Table 1, 2 and 3). It shows that Dh-86 genotype has more resistance to moisture stress and G2-52 was more sensitive to moisture stress. That is why there was reduction in the yield and growth attributes compared to other genotypes. In line with these results, significant genotypic variation for the traits related to drought tolerance was reported in numerous reports depending upon the material used in the study for groundnut genotypes (Vorasoot et al., 2003; Puangbut et al., 2009; Painwade et al., 2009).
       
Interaction effects indicated that I₁G₁ i.e., seven irrigations at 15 days interval given to genotype Dh-86 recorded higher yield (3191 kg ha^-1), but this treatment interaction was found at par with I₂G₁ i.e., skipping one irrigation at 45-60 DAS for Dh-86 (3168.0 kg ha^-1). However, skipping more irrigation reduced yield of all the genotypes including Dh-86 (Table 3).