Influence of Irrigation Scheduling and Nutrient Application on Water Use, Productivity and Profitability of Groundnut (Arachis hypogaea L.)

India is one of the largest producers of oilseeds in the world and plays an important role in Groundnut (Arachis hypogaea L.) is an important oilseed crop in India which occupies first position in terms of area and second position in terms of production with a cultivated area of 5.34 million hectares and production of 7.46 million tons with an average productivity of 1398 kg ha^-1 during 2016-17. Tamil Nadu ranks third in the country both in area (2.82 lakh hectares) and production (5.91 lakh tons) with an average productivity of 2084 kg ha^-1 during 2016-17. Timely availability of assured irrigation and nutrient management are the important factors that determine the productivity of the groundnut especially during the critical stages (flowering and peg formation stage). Continuous application of inorganic fertilizers is uneconomical considering the increase in prices of chemical fertilizer. Rice husk is the natural sheath and it is about 20 per cent by the weight of the rice harvested and in it 80 per cent by weight of the raw husk is made of organic components. Annual rice husk available in India is approximately 24 million tons (Shwetha et al., 2014). Incorporation of rice husk into soil was found to exhibit beneficial effect on a variety of crops (Sharma et al., 1984). Charred rice husk is a unique adsorbent material with diffusion and catalytic properties characterized by 20 to 30 per cent pore space. Arbuscular mycorrhiza is known to form mutualistic relationships with more than 80 per cent of crop plants. Beneficial effects on application of NPK with soil amendment of charred rice husk along with seed treatment of Arbuscular mycorrhiza is an opportunity to increase the crop productivity due to their combined and synergistic effects that help to concurrently improve physical, chemical and biological properties of soil. Present investigation was carried out to study the influence of irrigation scheduling and nutrient management practices with soil amendment of charred rice husk and seed treatment of Arbuscular mycorrhiza on productivity and water use efficiency of groundnut.

Field experiments were conducted at AC and RI, TNAU, Madurai to find out the efficient irrigation scheduling and nutrient management practices with charred rice husk and seed treatment with Arbuscular mycorrhiza in groundnut. The time of sowing was 16.02.2017, 06.08.2017 and 21.12.2017 during summer, kharif and rabi 2017 and the date of harvesting was 02.06.2017, 20.11.2017 and 18.04.2018 during summer, kharif and rabi, respectively. The total quantity of water applied during summer (400, 250 and 250 mm), kharif (200, 150 and 100 mm) and rabi (450, 350 and 250 mm) for IW/CPE ratio 0.8, 0.6 and 0.4, respectively. A total rainfall of 132.2, 372.8 and 16.6 mm were received during summer, kharif and rabi 2017, respectively. The soil of the experimental field was sandy loam in texture and belongs to vylogam series. The soil was low in available nitrogen (151.50, 158.75 and 156.00 kg ha^-1), medium in available phosphorus (21.20, 24.00 and 23.00 kg ha^-1) and high in available potassium (191.50, 199.50 and 197.00 kg ha^-1). The experiment was laid out in a split plot design with three replications. The main plots consisted of three levels of irrigation scheduling viz., I1- 0.8 IW/CPE ratio,  I2- 0.6 IW/CPE ratio and I3- 0.6 IW/CPE ratio and sub plot comprised of four level of nutrient management namely N₁ - 75% of RDF + 5 t ha^-1 of charred rice husk, N₂ - 50% of RDF + 5 t ha^-1 of charred rice husk, N₃ - 75% of RDF + 5 t ha^-1 of charred rice husk with seed treatment of Arbuscular mycorrhiza and N₄ - 50% of RDF + 5 t ha^-1 of charred rice husk with seed treatment of Arbuscular mycorrhiza. Groundnut cultivar ‘VRI-2’, a bunch variety having duration of 100-110 days was used. The seeds were treated with Arbuscular mycorrhiza culture at 10g ha^-1 of seeds. A seed rate of 125 kg kernel ha^-1 was used. Spacing of 30 cm between rows and 10 cm between plants was adopted. A plot with recommended dose of fertilizer along with irrigation scheduling at 1.0 IW/CPE ratio was maintained outside the experimental plot for comparison. Triple channel lay out was adopted for main plot treatments so as to eliminate the effect of lateral seepage. For every irrigation, 50 mm of water was applied to each plot using Parshall flume in closed channels. Daily readings of evaporation were recorded from USWB class “B” open pan evaporimeter and irrigations were scheduled based on IW/CPE ratio, as cumulated over days since previous irrigation by subtracting effective rainfall received during that period. Soil amendment i.e., charred rice husk was applied at 5 t ha^-1 (moisture free) incorporated well in the field before sowing of crops. The entire quantity of nutrients (N, P and K) i.e., 25:50:75 kg ha^-1 was applied as basal before sowing of seeds. Growth parameters like plant height, leaf area index and dry matter production and yield attributes viz., number of pods plant^-1, grain yield and haulm yield were recorded and the experimental data collected were subjected for statistical analysis for split plot design as suggested by (Gomez and Gomez. 1984).
 

Effect of irrigation scheduling and nutrient management practices on growth attributes
 
Plant height and dry matter production was influenced by irrigation scheduling and nutrient management practices (Table 1 and 2). The Significantly taller plants of 47.70, 47.03 and 48.66 cm and dry matter production of 5079, 4851 and 5103 kg ha^-1 at harvest during kharif, rabi and summer, respectively were observed with irrigation scheduling at 0.8 IW/CPE ratio and it was comparable with irrigation scheduling at 0.6 IW/CPE ratio. The increased soil moisture availability to the crop might have provided optimum moisture supply and uptake by the crop resulting in increase in cell division, stem elongation and finally increased plant height and dry matter production. Earlier works of Hallikeri et al., 2009: Ahlawat and Gangaiah. 2010 corroborates with the above findings. The shorter plants were observed with irrigation scheduling at 0.4 IW/CPE ratio. The decreased soil moisture availability owing to decreased water supply at irrigation scheduling at 0.4 IW/CPE resulted in stunted growth, probably due to decreased absorption of water, leading to poor growth. The results of reduced moisture supply resulting in reduced plant height and dry matter production has been reported by Hassan et al., 2016.




 
Among the nutrient management practices, the higher plant height and dry matter production was observed with application of 75% of RDF adding with 5 tons of charred rice husk along with seed treatment of Arbuscular mycorrhiza with a plant height of 49.26, 46.32 and 48.25 cm and dry matter production of 5030, 4805 and 4998 kg ha^-1 during kharif, rabi and summer, respectively. Application of charred rice husk along with adequate moisture might have increased the microbial activity due to presence of adequate carbon in the soil and provide good microclimatic environment in the rhizosphere. Further, conjugation of Arbuscular mycorrhiza could have paved way for increased availability of nutrients resulting in enhanced root growth. It also creates more adsorptive surface for uptake of nutrients by the crop. Hogan. 2011; Zhang et al., 2014 reported that increased growth parameters due to application of charred rice husk along with inorganic fertilizers. The lower plant height and dry matter production was recorded with application of 50% of RDF along with 5 t charred rice husk during all the seasons. 
 
Effect of irrigation scheduling and nutrient management practices on yield       
                                                                  
Irrigation scheduling at 0.8 IW/CPE ratio recorded the higher pod yield and haulm yield of 2005 and 4841 kg ha^-1 during kharif, 1890 and 4810 kg ha^-1 during rabi and 1869 and 4828 kg ha^-1 during summer 2017, respectively (Table 3 and 4). This was comparable with irrigation scheduling at 0.6 IW/CPE ratio. This might be due to charred rice husk could act as a medium for adsorption and desorption of plant nutrients, besides providing favourable conditions for soil microorganisms. This might have resulted in higher carbon, phosphorus and potassium availability to plants with greater stabilization of organic matter, concurrent with slower nutrient release from the added organic matter. The better retention of cations due to greater cations exchange capacity could have also resulted in immediate beneficial effects of soil nutrient availability resulting in higher value of crop growth parameters viz. plant height, leaf area index, dry matter production which ultimately reflected in yield attributes viz., number of flowers, total number of pods per plant and pod yield. The present findings are in consonance with the findings of Zhang et al., 2014; Kannan et al., 2016. The lower pod yield (1481, 1357 and 1328 kg ha^-1 during kharif, rabi and summer, respectively) and haulm yield (4038, 4153 and 4227 during kharif, rabi and summer, respectively) was observed with irrigation scheduling at  0.4 IW/CPE ratio during all the seasons.





With respect to nutrient management practices, application of 75% of RDF in combination with 5 t of charred rice husk along with seed treatment of Arbuscular mycorrhiza recorded the higher pod yield (1935, 1854 and 1783 kg ha^-1 during kharif, rabi and summer, respectively) and haulm yield (4779, 4790 and 4743 kg ha^-1 during kharif, rabi and summer, respectively). This was followed by application of 50% of RDF with 5 t of charred rice husk along with seed treatment of Arbuscular mycorrhiza. The presence growth promoting substances due to colonization of Arbuscular mycorrhiza promoted plant growth and could have increased the chlorophyll production by boosting the photosynthetic process and stimulating vegetative growth. Thus, an overall plant performance would have enhanced accordingly and finally reflecting through increased production of haulm (Gouda et al., 2018).
 
Interaction between irrigation scheduling and nutrient management practices also significantly influenced the pod yield. Among the irrigation scheduling and nutrient management practices, the pod yield was highest with the combination of irrigation scheduling at 0.8 IW/CPE ratio along with 75% of RDF and 5 t of charred rice husk along with seed treatment of Arbuscular mycorrhiza with a pod yield of 2003, 2099 and 2063 kg ha^-1 during summer, kharif and rabi 2017 respectively. Whereas, the lowest pod yield was recorded with irrigation scheduling at 0.4 IW/CPE ratio along with 75% of RDF and 5 t of charred rice husk.
 
Effect of irrigation scheduling and nutrient management practices on water use efficiency
 
The maximum water use efficiency was recorded under irrigation scheduling at 0.8 IW/CPE ratio with a value of 4.16, 7.07 and 4.86 kg ha^-1mm^-1 during summer, kharif and rabi 2017, respectively (Table 5, 6 and 7). The higher water use efficiency at irrigation scheduling at 0.8 IW/CPE ratio might have largely resulted from constant soil moisture content at or near field capacity level and adding of charred rice husk improved physical soil properties, such as increased soil aggregations, water holding capacity, decreased soil strength and percentage water holding capacity, that enhanced by the carbonization process, resulting in increase in water retention. These findings are in conformity with those of (Srivastava and Chauvan 1995) in groundnut. The nutrient management practices had also exerted its influence on water use efficiency in all the experimental seasons. Application of 75% of RDF with 5 t of charred rice husk along with seed treatment of Arbuscular mycorrhiza recorded the maximum water use efficiency of 3.94, 6.83 and 4.74 kg ha^-1mm^-1 during summer, kharif and rabi 2017, respectively. The minimum water use efficiency was recorded in 50% of RDF with 5 t of charred rice husk.






 
Effect of irrigation scheduling and nutrient management practices on water productivity
 
Imparting different irrigation scheduling noticeably influenced the water productivity of groundnut crop in all the three seasons and the data are furnished in Table 5, 6 and 7. The lower water productivity (₹214.03 and 227.83 m^-3 during summer and rabi 2017, respectively) was recorded with irrigation scheduling at 0.8 IW/CPE ratio. However, during kharif’ 2017, irrigation scheduling at 0.8 IW/CPE ratio recorded higher waters use efficiency of ₹257.35 m^-3. Among the nutrient management practices, application of 75% of RDF along with 5 t of charred rice husk and seed treatment with Arbuscular mycorrhiza recorded the higher water productivity during all the three seasons.

Effect of irrigation scheduling and nutrient management practices on economics

With an increase in irrigation frequency, the total expense on cultivation increases consequently (Table 8, 9 and 10). The irrigation scheduling at 0.4 IW/CPE ratio along with application of 50% of RDF incurred the lowest cost of cultivation of ₹49500 ha^-1, ₹ 48100 ha^-1 and ₹49500 ha^-1 during summer, kharif’ and rabi 2017, respectively. While, the highest cost of cultivation was recorded with treatment of irrigation scheduling at 0.8 IW/CPE ratio and application of 75% of RDF with 5 t charred rice husk along with seed treatment of Arbuscular mycorrhiza during all the three field experiments. The highest Gross return (₹116127, 126605 and 117756 ha-1 during summer, kharif and rabi 2017, respectively), net return (₹62127, 74605 and 63756 ha^-1 during summer, kharif and rabi 2017, respectively) and B:C ratio of 2.2, 2.4 and 2.2 during summer, kharif and rabi 2017 respectively were registered with irrigation scheduling at 0.8 IW/CPE ratio and application of 75% of RDF with 5 t of charred rice husk along with seed treatment of Arbuscular mycorrhiza. This could be ascribed to higher expenses incurred to organic amendment and lower marginal returns with these sources. Improvement in soil health due to continuous application of soil amendment, if converted into monetary term, would definitely provide higher returns. Similar finding was also reported by (Verma et al., 2003).

From the present investigation, it can be concluded that irrigation scheduling at 0.8 IW/CPE ratio along with 75% of RDF and 5 tons of charred rice husk as basal with seed treatment of Arbuscular mycorrhiza would be an ideal practice for improving water use efficiency, getting higher yield and economic returns.

All authors declare that they have no conflicts of interest.