Yield Response Factor for Onion ( Allium Cepa L ) Crop Under Deficit Irrigation in Semiarid Tropics of Maharashtra

The present study deals with the study of yield response factor (Ky) for onion crop cultivated under deficit irrigation for Rahuri region (Maharashra). The field experiment was conducted to determine the yield response factor of the onion (Allium cepa L.) cv. N-2-4-1 crop under the deficit irrigation approach during summer season of 2012 and 2013 at Instructional Farm of the Department of Irrigation and Drainage Engineering, Dr. Annasaheb Shinde College of Agricultural Engineering, Mahatma Phule Krishi Vidyapeeth Rahuri. Experiment was carried out in Randomized Block Design (RBD) with 27 treatments and two replications based on different combinations of the quantity of water stress during different crop growth stages. Water applied per irrigation and soil moisture contents before and after irrigation were monitored throughout the season, while onion bulbs were harvested at the end of season and weighed. Average daily crop water use (crop consumptive use) were estimated from the soil moisture content using the soil moisture depletion method. The seasonal yield response factor (Ky) was obtained by relating relative yield decreases to relative crop water use deficit by the regression analysis. The relative yield decreases of the onion crop were proportionally greater with increase in evapotranspiration deficit. It shows the response of yield with respect to the decrease in water consumption. In other words, it explains the decrease in yield caused by the per unit decrease in water consumption. Seasonal crop response factor for onion crop was determined as 1.58, 1.48 and 1.54 during 2012, 2013 and average of both year (2012 &2013) respectively. The yield response factors developed in this study could be used in irrigation design and scheduling for onion in the study area. key words: Onion, Deficit Irrigation, Crop Coefficient (Kc), Yield Response Factor (Ky), Crop Water Use.


InTRODUCTIOn
Onion (Allium cepa L.) is one of the important vegetable crops commercially grown in India.India is the second largest producer of onion in the world, next only to China.The total area under onion in India is 1064000 ha and the total production is 15118000 MT.India accounts for 26.8 per cent the total area and 19.9 per cent the total production of the world.The average productivity of the world is 19.1 MT/ha while India being the second major onion producing country in the world has a productivity of 14.2 MT/ha (Source FAO Website: March 2012 and Indian Horticulture Database 2011).Maharashtra is the leading onion grower and producer state in the country which accounts 39 per cent of the total area and 32.5 per cent national production followed by Karnataka, Gujarat etc.The area under onion in Maharashtra is 415000 ha and the onion production is 4905000 MT.In India per hectare yield is highest in Gujarat (24.4 MT/ha) followed by Haryana (20.5 MT/ha), Bihar (20.3 MT/ha), Madhya Pradesh (17.5 MT/ha) whereas, in Maharashtra it is 11.8 MT/ ha.(Source FAO Website: March 2012 and Indian Horticulture Database 2011).
Abiotic stresses can directly or indirectly affect the physiological status of an organism by altering its metabolism, growth and development and adversely affect the agricultural productivity (Bartles and Sunkar 2005, Vibhuti et al 2015, Shahi et al 2015a).Water is the main limiting factor for production of many crops including onion in the arid and semiarid regions.Fresh and dry mass production of crop may reduce due to the adverse effect of water stress (Shahi et al 2015b).When water resources are scarce, deficit irrigation is one way of maximizing water use efficiency (Bekele and Tilahun 2007).Deficit irrigation is the practice of irrigating crops deliberately below their water requirements.Such practice is aimed at minimizing water applied to the crop so as to maximize crop yield per unit of water applied.This may however lower the yield per unit area.Many research works have been carried out to study the consequences of deficit irrigation on onion crop (Olalla et al., 1994;Gorantiwar and Smout.,2003;Pelter et al., 2004;Mermoud et al., 2005;Bekele and Tilahum, 2007;Ouda et al., 2010;and Pejiae et al., 2011).
A research gap in the region where onion is produced in Maharashtra is the knowledge of water requirement of the onion crop under deficit irrigation.Moreover, the consequences of deficit irrigation regimes are yet to be fully understood.Two key parameters commonly required in determining crop water requirement and predictions of yield-water response to deficit irrigation are crop coefficient (Kc) and yield response factor (Ky).The yield response factor (Ky) is ratio of relative yield reduction to relative evapotranspiration deficit.It is the factor that integrates the weather, crop and soil conditions that make crop yield less than its potential yield in the case of deficit evapotranspiration.The yield response factor Ky is commonly required as input data in some empirical water production functions like (Jensen, 1968) and (Stewart et al., 1977) to predict crop yield response to water.
In order to determine the yield response factor of onion crop for Rahuri region (Maharashtra) the present study was carried out by raising the onion crop under different regimes of deficit irrigation approach.It is anticipated that the information generated in this study will be useful for developing crop water requirements for irrigated onion under deficit irrigation regimes and for the overall improvement of irrigation water management for onion in the study area.

Crop water use
Number of irrigations and gross depth of irrigation water applied to each treatment are given in Table1.

Onion yield as influenced by water stress
The mean pooled onion yield for two two season for all the treatments are given in Table 2.The yield data were analyzed statistically for randomized block design.The yields were statistically significant.The mean yields along with CD at 5 % are presented in Table2.
It is observed from above table that the higher yields are observed in trématent T1 (0% stress at vegetative stage,bulb development stage and bulb enlargement stage) followed by T4, T3, T10, T11, T5, T20, T21, T12, T19, T6, T16, T7, T13, T8, T22, T15, T18, T9, T17, T18, T23, T14, T24, T25, T26 and T27.The onion yields are lowest for T27 (40% stress at vegetative stage, bulb development stage and bulb enlargement stage).However, the yields of treatments T1 and T4, T2, T3 and T10 are at par.The yields of treatments T5, T11, and T20 are at par.The yields of treatments T6, T7 and T16 are at par.The yields of treatments T8, T13, T15 and T22 are at par.The yields of treatments T15, T8, T14, and T22 are at par.The yields of treatmentsT9, T17, T23 and T24 are at par.Statistically shows that the vegetative stage of the onion crop with no water stress gives higher onion yield at C.D.5%.Thus, the onion yields are higher with less water stress and reduce with increase in water stress.

Yield response factor (ky)
Table 3, 4 and 5 shows the relative decreases in seasonal crop water use and bulb yield for 2012, 2013 season and average of two seasons.Yield response factor (Ky) indicates a linear relationship between the decrease in relative water consumption and the decrease in relative yield.It shows the response of yield with respect to the decrease in water consumption.In other words, it explains the decrease in yield caused by the per       Crop yield response factor (Ky) indicates a linear relationship between the decrease in relative water consumption and the decrease in relative yield.It shows the response of yield with respect to the decrease in water consumption.In other words, it explains the decrease in yield caused by the per unit decrease in water consumption.
The moisture content observations during 2012 and 2013 were recorded before irrigation, after irrigation and during irrigation period for all the treatments for the purpose of computing the actual evapotranspiration.The treatment T1 was treatment without water stress and hence actual evapotranspiration of treatment T1 was considered as maximum crop evapotranspiration.The maximum crop evapotranspiration during 2012 and 2013 and average of 2012 and 2013 were computed.These are 529, 556 and 543 mm for 2012, 2013 and average of 2012 and 2013 respectively.The treatments T2 to T27 were treatments with some stress.The values of actual evapotranspiration along with maximum onion evapotranspiration are presented in Tables 3,4 and 5.These tables show the relative decreases in seasonal crop water use and bulb yield for onion crop during 2012 and 2013 seasons and average of two seasons The relationship between relative yield reduction and relative evapotranspiration deficit for  Doorenbos and Kassam (1986).They reported that seasonal yield response factor (Ky) value of 1.50 for onion during the whole growing season.Generally, higher Ky values indicate that the crop will have a greater yield loss when the crop water requirements are not met.This result indicated a high impact of soil-water stress treatment on the onion yield.Therefore, water management of onion is extremely important at all stages of plant growth.

1.
The results indicated a high impact of soilwater stress treatments on the onions yield.

2.
The crop water use of the onion crop decreased with increase in irrigation deficit.

3.
The yield response factor (Ky) for onion in semi arid tropics of Maharashtra was found to be 1.54 for whole growing season.
...(1) Where, FC = field capacity, % MC = moisture content at the time of irrigation, % BD = bulk density of soil, g/cc D = effective root zone depth, cm Irrigations were scheduled at every growth stage of onion crop as per stress underlined in each treatment.The stress was estimated from the moisture content stress in the rootzone.The depths of irrigation water were applied according to the treatments.The yield response factor was computed using the Doorenbos and Kassam (1979) equation re-arranged as, ...(2) Where Ya = actual yield (t/ha), Ym = maximum yield (t/ha), Eta = actual evapotranspiration (mm) ETm = maximum evapotranspiration (mm).Ky = yield response factor of onion to deficit irrigation.

Fig. 1 :
Fig.1: The relation between reduction in relative onion yield to reduction in relative evapotranspiration (2012)

Fig. 2 :
Fig. 2: The relation between reduction in relative onion yield to reduction in relative evapotranspiration (2013)

Fig. 3 :
Fig. 3: The relation between reduction in relative onion yield to reduction in relative evapotranspiration (average).

Table 5 : Average relationship between the decrease in relative water use and decrease in relative yield for onion during 2012 and 2013 season.
shown in Figures 1, 2 and 3.The yield response factor (Ky) for onion in 2012, 2013 and average of 2012 & 2013 by regression analysis was found to be 1.58, 1.48 and 1.54 for whole growing season.Result obtained was in agreement with those reported by