Effect of Moisture Regimes on Water use Efficiency of Rabi / Summer Groundnut Genotypes in Northern Transition Zone of Karnataka

Groundnut (Arachis hypogaea L.) is an oilseed crop grown in almost all the tropical and sub-tropical countries of the world. Developing countries in the semi-arid tropics (SATs) together contribute 50 per cent of global production of which only India and China have 30 and 20 per cent share to make up half the share. In India, groundnut alone accounts for 45 per cent of the total oilseed area and 60 per cent of the total oilseed production and is cultivated in all the three seasons viz., rainy (85%), post-rainy (10%) and summer (5%). In India, it is grown in 27 states on an area of 4.88 million ha with a production of 9.25 million tonnes and with an average productivity of 1893 kg ha^-1 (Anonymous 2019). In Karnataka, groundnut is grown on area of 5.80 lakh hectares with a production of 4.23 lakh tonnes with the productivity of 729 kg ha^-1 (Anonymous 2019).
       
The productivity of Karnataka is very low compared to national average as most of the area is under rainfed and being an unpredictable legume, shows inconsistency in pod and oil yields. Further, it has been proved that water is most critical input that affects crop growth and yield and its scarcity leads to great reduction in productivity of groundnut especially during rabi / summer season. Research efforts need to be strengthened to narrow down the existing yield gap by management practices (e.g., irrigation) and selection of suitable genotypes to enhance yield. To sustainably alleviate the moisture deficit effects and improve groundnut production, it is imperative to identify suitable cultivars. The varieties should be able to provide higher yield and water use efficiency under moisture stress situation. In this context, an experiment was conducted to study the effect of moisture regimes on yield and yield attributes, economics and water use efficiency of groundnut genotypes for Northern Transition Zone of Karnataka.

A field experiment was conducted during rabi / summer (December to April) 2016-17 at 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 two irrigations at 45-75 DAS, I₄: Stress at pegging, pod filling and kernel development stage i.e., withdrawal of four 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 (0.21 dS 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 was much lower than long-term average.
 
Total number of pods produced plant^-1 was counted in all the five plants and average per plant was worked out. The developed pods were dried completely (up to 8% moisture level) and weighed. On the basis of pod yield for net plot, the pod yield ha^-1 was calculated. After plucking the pods from harvested groundnut plants, the remaining produce was sun dried to constant weight and haulm yield plot^-1 was recorded. From each net plot produce, 200 g of clean pods were weighed and kernels were obtained after shelling. Shelling per cent was worked out by dividing kernel weight by pod weight and expressed in percentage. After shelling the pods, 100 kernels were randomly taken and weighed. To workout the cost of cultivation, the price of the inputs that were prevailing at the time of use was considered and expressed in rupees per hectare (₹ ha^-1). The price of the crop products prevailing in the  market after the harvest was used for the calculation of gross returns (₹ ha^-1) and the net returns per hectare was calculated by deducting the cost of cultivation from the gross returns and expressed in rupees per hectare (₹ ha^-1). The water use efficiency was calculated by dividing crop yield by total amount water used in the field and expressed as kg/ha-mm. 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).

Effect of moisture stress on yield and yield attributes of groundnut genotypes
 
The pod yield depends on yield components which in turn depends upon the growth and yield attributes. The practical way of judging the efficacy of the treatments in any agronomic experiment is by comparing the yield variations. Moisture stress at different growth stages of crop had a significant influence on yield and yield attributes. Stress at pegging stage (I₂) recorded higher pod yield and haulm yield (2,857 kg ha^-1 4,648 kg ha^-1, respectively) and other yield attributes. However, it was at par with (I₁ water regime) no moisture stress crop (2,869 kg ha^-1 and 4691 kg ha^-1). The higher pod yield and haulm yield in I₂ was due to better yield attributes like pod yield plant^-1 (10.10 g plant^-1) (Table 2), number of pods plant^-1 (20.6 plant^-1) and test weight (33.1g) (Table 1). It might be due to the fact that groundnut plants compensate for earlier drought period by initiating a flush of reproductive parts after the relief of stress (Dutta and Mondal, 2006). It’s been reported that water stress during the vegetative or early flowering stages is not detrimental and sometimes actually increases yield (Rao et al., 1985; Nautiyal et al., 1999). However, 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 32.0% (1,950 kg ha^-1) and 70.6% (842 kg ha^-1) respectively, over the no moisture stress (I₁). It might be due to inadequate availability soil moisture at reproductive stages, like pod filling and kernel development stages, as these are the critical stages for crop which hinders the translocation of photosynthates from leaves to fruiting parts and affect the pod formation and pod yield. This results in lower number of pods plant^-1, lower pod dry weight plant^-1 and lower kernel hundred weight (Assan and Sani, 1985). Moisture stress during seed filling stage is known to accelerate the rate of seed maturation causing yield loss due to shortened grain filling phase (Boote et al., 2003). A slight reduction of water requirement of groundnut does not significantly affect the pod yield. However, above 20 per cent water stress affects the pod yield (Aruna et al., 2017).There was a significant difference among the different water regimes with respect to shelling percentage, I₁ (no stress) recorded significantly higher shelling percentage (69.6%), but was found on par (68.9%) with the treatment I₂ (stress at pegging stage).
       

 

 
The perusal of yield data revealed that groundnut yield differed significantly among the groundnut genotypes. The genotype Dh-86 (2,375 kg ha^-1) recorded significantly superior pod yield over other genotypes like Dh-101 (2,215 kg ha^-1), K-9 (2,048 kg ha^-1) and G2-52 (1,880kg ha^-1). The increase in grain yield of Dh-86 over other genotypes was to the extent of 6.75 per cent, 13.77 per cent and 20.84, per cent, respectively. The increased in the pod yield (2,375 kg ha^-1) and haulm yield (3,815 kg ha^-1) was due to higher yield parameters like number of pods per plant (20 plant^-1) and kernel weight (32.2 g) (Table 1). Among the different genotypes, Dh-86 (G₁) recorded significantly higher shelling percentage (67.8%) and the lowest shelling percentage was recorded with G2-52 (G₄) (64.6%), respectively (Table 1). Similar type of findings with different cultivars suggesting differential response were observed by Vorasoot et al., (2003).
 
Interaction effects indicated that Dh-86 with stress at pegging stage recorded significantly higher pod yield (I₂G₁, 3168.0 kg ha^-1), which was at par with the I₁G₁ (3191.3 kg ha^-1). It might be due to higher number of pods and shelling percentage. Higher haulm yield was recorded in I₂G₁ (4881.3 kg ha^-1), which was at par with the I₁G₁ (4910.3 kg ha^-1). This might be due to more dry matter production per plant and more leaves and more dry weight of stem plant^-1 leads to higher haulm yield.
 
Effect of moisture stress on water use efficiency of groundnut genotypes
 
Water use efficiency (WUE; kg/ha-mm) was influenced by different water regimes and presented in Table 3. Stress at pegging stage (I₂) recorded significantly higher WUE (6.2 kg/ha-mm) followed by (I₁) no stress (5.5 kg/ha-mm) while, stress at pegging, pod filling and kernel development stage (I₄) recorded significantly lower WUE (2.5 kg/ha-mm). Among the genotypes, Dh-86 (5.3 kg/ha-mm) recorded the significantly higher WUE over other genotypes and the least was observed in G2-52 (4.2 kg/ha-mm). Cultivation of genotype Dh-86 with stress at pegging stage (I₂) recorded the significantly higher WUE (6.9 kg/ha-mm) compared to other treatment combinations (Table 3). Field WUE and dry matter production, including economic yield were increased by imposing a transient deficit in soil moisture during the vegetative phase in groundnut (Nautiyal et al., 2017).
 
 

 
Effect of moisture stress on economics of groundnut genotypes
 
Higher gross return (₹ 1,24,670 ha^-1) and net return (₹ 82,388 ha^-1) were recorded with I₂ (stress at pegging stage). However it was at par with no moisture stress treatment (I₁). It was mainly due to higher pod yield and higher haulm yield (Table 3). Among the various genotypes Dh-86 (G₁) was recorded significantly higher gross return (₹ 1,03,594 ha^-1) and net return (₹ 62,055 ha^-1) compared to other genotypes. This was attributed to higher pod yield and haulm yield resulting in higher net return and gross return compared to other genotypes. Among interactions, significantly higher gross return (₹ 1,37,937 ha^-1) and net return (₹ 95,655 ha^-1) was recorded with I₂G₁ which was at par with the I₁G₁ (₹ 1,38,946 ha^-1 and ₹ 95,639 ha^-1).

The results showed that mild deficit moisture regime at pegging is feasible, but the same stress at pegging, pod filling and kernel development stage (I₄) are not feasible. It negatively affects yield and yield attributes and profitability of groundnut production in the NTZ of Karnataka. From this experiment it can be concluded that cultivation of genotype Dh-86 with mild stress at pegging stage (I₂) by skipping one irrigation could be the best condition for groundnut production to improve net profit of production and enhance WUE.

The authors sincerely thank and acknowledge All India Coordinated Research Project (AICRP) on Groundnut, UAS, Dharwad for extending all logistical resources for this field research work.