Water use efficiency of Brassica cultivars under rainfed conditions of Pakistan.

Dr. Fayyaz-ul-Hassan and Abdul Manaf

University of Arid Agriculture, Rawalpindi, Pakistan
E-mail. munafawan@yahoo.com, drsahi63@yahoo.com

Abstract

Water use efficiency (WUE) is the ratio of grain yield to crop water use. Two years study (2003-04 & 2004-05) was carried out at three locations (Rawalpindi, Chakwal & Attock) in rainfed region of Pothwar, Pakistan. Ten brassica ( five local and five exotic) cultivars were sown in randomized complete design replicated four times. Brassica cultivars depicted significant differences for WUE during both the years i.e. 2003-04 and 2004-05 (pooled over locations). Similarly, locations mean (pooled over year) had significantly affected WUE. Interactive effects of cultivar x year, cultivar x locations and cultivar x year x locations had exerted significant effects on WUE. Statistically significant differences among cultivars may be related to genetic make up of the cultivars. The differences between years could be due to total precipitation received during crop life cycle. Increased precipitation received during crop life cycle decreased the WUE thus depicted an inverse relationship between total rainfall and WUE.

Key words

Water use efficiency, brassica, locations, rainfed, precipitation

Introduction

Canola is generally considered to be more susceptible to drought than wheat. However, water deficiency produces different consequences according to the stage of the crop cycle and the magnitude of the deficiency. The yield is mainly affected by water shortage which occur during flowering to the end of seed setting.

Water use is usually considered as evaporation (E) plus transpiration (T), while runoff and drainage are often negligible in dryland areas and are ignored. Water use and most of soil moisture is lost early in the season when the crop biomass and ground cover are small (Siddque et al. 1990). Water use can be increased by i) increasing T relative to E, ii) increasing soil water uptake. Any strategy that increases the rate of canopy closure should increase the proportion of T relative to ‘E and thereby increase dry matter production and yield (Turner, et al., 2001). Differences in WUE among crop species are related to the carboxylation pathway and energy required to produce dry matter whereas apparent differences between cultivars of the same species can be related to differences in soil evaporation and chemical composition of dry matter (Ludlow and Muchow, 1990)

Brassica napus has been introduced in Pakistan during last decade. It has shown be a potential crop particularly under rainfed conditions where all agriculture depends on rains. However, availability of rains is highly erratic and uncertain. Under such conditions the cultivation of brassica at random will not be a good agronomic practice. Therefore, keeping in view the potential of brassica under rainfed conditions, the present study was planned to earmark the most potential cultivars those have higher water use efficiency particularly under limited water availability.

Materials and Methods

Field experiments were conducted at three locations i.e the University of Arid Agriculture, Rawalpindi (Rwp), Groundnut Research Station Attock (Atk), and Barani Agricultural Research Institute Chakwal (Chk), during 2003-04 and 2004-05. The experimental sites are located at, Rawalpindi (33⁰36 min, 73⁰ 05 min, average annual rainfall 1000-1200 mm/annum), Attock (33⁰ 46 min, 72⁰ 21 min, average annual rainfall 650-850 mm/annum) and Chakwal (32⁰ 56 min, 72⁰ 51 min, average annual rainfall 450-550 mm/annum).

The seed of ten canola varieties viz. Shiralee, Westar, Dunkeld, Zafar-2000, Bulbul-98, Con-II, 19-H, Abaseen, Rainbow and Con-I were sown in a randomized complete block design with four replications. The experiments were sown at three locations in a net plot size 5 m x 2.7 m on 14-10-2003, 13-10-2003, 16-10-2003 at Rawalpindi, Attock and Chakwal, respectively, during 2003-04 and on 28-10-2004, 14-10-2004, 16-10-2004 at Rawalpindi, Attock and Chakwal, respectively, during second year (2004-05). Recommended dozes of fertilizer i.e. 80 kg N and 60 kg P₂O₅ per hectare were applied at the time of last plowing. Phosphorus was applied in the form of Diammonium phosphate (DAP) and nitrogen in the form of urea and DAP. Crop was sown with hand drill using five kg seed per hectare keeping 45 cm distance between rows. After complete emergence, crop was thinned manually to maintain approximately 16 plants per meter row length. At maturity, the central two rows were harvested manually on 06-04-2004 at Rawalpindi, 01-04-2004 at Attock, 03-04-2004 at Chakwal during first year and on 20-04-2005 at Rawalpindi, 16-04-2005 at Attock and 19-04-2005 at Chakwal during second year. Harvested plants were tied into small bundles and kept upright along the wall for sun drying. Daily maximum and minimum temperatures (⁰C) and rainfall (mm) were recorded during the course of study at nearby weather stations at experimental sites. Soil moisture was determined by gravimetric method (Hesse, 1971). Water use efficiency was calculated by using the following formula as proposed by Gregory, (1991).

WUE = [SY/ WU]

SY = Seed Yield

WU = Water used

Water used was the difference in soil moisture measured at the start of the trial and at the end of the trial.

Results

Mean WUE of brassica cultivars at three locations pooled over years showed differential response (Table 1). Among locations the WUE was observed to be the lowest at Attock, whereas, the highest at Chakwal while Rawalpindi exhibited an intermediate response. Jerry et al. (2001) concluded that variation for water use efficiency at particular during particular year is mainly due to variation for total precipitation received at particular location. Thus our findings are consistent to above conclusion. Brassica cultivars depicted significant differences for water use efficiency (WUE) pooled over locations during both the years i.e. 2003-04 and 2004-05. During 2003-04, cultivar Shiralee and 19-H exhibited the highest WUE of 15.7, 15.3, respectively, those were statistically significant from rest of the cultivars. (Table 1). During year 2004-05, the highest (7.99) WUE was observed for Zafar-2000 which statistically differed from rest of the cultivars. Average WUE and variability among cultivars decreased during second year. The differences in water use efficiency may be due to different genetic potential of each cultivar. However, reduction of WUE during second year may be attributed to more rains recorded during reported period which were more than the requirement of the crop (Table 1).

Table 1. Water use efficiency of brassica cultivars at three locations (pooled over years) during 2003-04 and 2004-05 (pooled over locations)

	Locations			Years
Cultivars	Rwp	Atk	Chk	2003-4	2004-5
Shiralee	11.1	7.14	14.9	15.7	6.38
Westar	9.79	6.08	10.9	12.5	5.42
Dunkeld	8.13	5.38	12.3	12.2	4.99
Zafar-2000	11.7	5.73	12.6	12.0	7.99
Bulbul-98	9.63	6.60	13.1	13.5	6.01
Con-II	9.23	5.18	13.4	12.7	5.85
19-H	11.9	6.73	14.4	15.3	6.72
Abaseen	8.00	7.02	11.1	11.7	5.69
Rainbow	7.78	8.53	8.0	10.7	5.50
Con-I	7.84	9.80	13.6	14.1	6.78

Mean	9.51	6.82	12.4	13.0	6.13

SE: Locations = 0.11, Interaction = 0.34, Cultivars = 0.19, Years = 0.09, Interaction = 0.27

Brassica cultivars exhibited differential response for water use efficiency at three locations during both the seasons (Table 2). Drastic changes in mean water use efficiency during both years were recorded in all cultivars at all three locations. However, range of variability was narrow at Rawalpindi. None of the cultivars showed consistent response during both the cropping seasons at three locations but interactions exhibited varying degree of differences. Findings of these experiments are consistent to those of Grey (1998) who reported the water use efficiency of canola in the range of 10-12. He further concluded that rainfall in excess of the crop requirement would lower the water use efficiency. Wide range of variability among cultivars and between years may be attributed to total precipitation received at each location and soil structure of particular location.

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