Abstract: In this experiment irrigation scheduling was done on the basis of cumulative pan evaporation (CPE). Wheat grown at seed rates of 100, 125 and 150 kg ha-1 was irrigated using IW:CPE ratios of 0.70, 0.90, 1.10 and 1.30. Data on agronomic traits like plant height, tillers m-2, grains spike-1, 1000-grain weight, grain yield, straw yield, harvest index and water use efficiency were collected. Statistical analysis suggested that wheat was quite responsive to increase in irrigation as well as seed rate. Increase in both treatments displayed an increase in plant population m-2, which was indicated in terms of tillers m-2. In other words highest irrigation and seed rate produced greater plant population m-2 and thus, the competition among plants was increased. Result was the reduction in important yield attributes like grains spike-1 and 1000-grain weight, which ultimately produced less grain yield at higher levels of experimental treatments. It was inferred that to obtain the maximum production of wheat it should be sown at the rate of 125 kg ha-1 and should be irrigated at IW:CPE ratio of 0.9.
Introduction
Wheat, being the most important cereal crop of Pakistan is widely grown all over the country due to its wider adaptability. Wheat is grown over an area of 8463 thousand hectares with a production of 21078.6 thousand tones (Anonymous, 2000). Its current average yield (2491 kg ha-1), however, is far below the genetic potential of the existing wheat cultivars. Low plant population and inadequate irrigation to the crop, among others, are the prime factors affecting the yield of wheat crop. Plant population is directly related to seed rate. Seed rate either below or above the optimum, reduces the yield. Low plant population (with lower seed rate) obviously produces less yield per unit area. High plant population (with higher seed rate) results a sort of nutritional competition among the plants, which at the end returns to a low production. It is speculated that maximum number of main tillers per unit area could be more productive as compared to secondary tillers. According to Wibberley (1989) secondary tiller production in wheat beyond a certain level is not considered a favorable factor because main stem spikes are always high yielders. Thus, there is a possible room to conduct research in this area. Generally increase in seed rate has been shown to increase the grain yield and its components in wheat. Ram et al. (1988) reported that when wheat was sown at 140 or 160 kg seed ha-1 gave average yields of 4.02 and 4.05 t ha-1 compared with 3.83 and 3.69 t ha-1 with sowing rates of 120 and 100 kg ha-1, respectively. Bhatnager et al. (1990) seeded wheat at the rate of 100, 125, 150, 175 and 200 kg ha-1 and observed that grain yield increased with the increase in seeding rate. Qaiser (1991) in an experiment compared different seeding rates and reported the highest grain yield of 53.42 kg ha-1 with 100 kg seed ha-1. Schoonwinkel et al. (1991) observed that when rain fed wheat was grown at seeding rates of 50, 75, or 100 kg ha-1, maximum grain yield was obtained at 100 kg ha-1. An increase in grain yield with increase in seeding rate was also reported by Singh et al. (1993) who found that seeding rates of 100, 125 and 150 kg seed ha-1 gave average grain yield of 2.72, 2.92 and 2.92 t ha-1, respectively.
Importance of water for crop plants is well established. Shortage of irrigation at critical stages alters the normal physiological functions and reduces the yield. Similarly, application of excessive water is the wastage of this valuable input. Application of water according to crop needs require proper scheduling. Actual amount of water needed by the crop is generally less than the amount applied during irrigation. Most of the water is lost through evapotranspiration or deep percolation. Thus, water use efficiency is decreased. It necessitates, finding out precise amount of water to be applied to achieve its efficient use.
The researchers have extensively used technique of cumulative pan evaporation (CPE) to calculate the amount of water to be applied. This technique is useful to estimate crop water needs for weekly or longer intervals. Pans of different size are used to obtain pan evaporation for a particular period of time. The pan evaporation value is then adjusted using a pan coefficient (kp) to obtain cumulative pan evaporation. Pan coefficient is dependent upon the temperature, relative humidity and wind velocity of that particular area. Pater et al. (1983) applied irrigation water to wheat at IW:CPE ratios of 0.6, 0.75, 0.9 or 1.05. They found that six irrigations each of 80 mm at an IW:CPE ratio of 0.9 gave the highest average grain yield of 3.42 t ha¯1 with WUE of 7.53 kg mm-1. Gill and Kenvain (1992) irrigated wheat crop grown on a sandy loam at IW:CPE ratios of 0.60, 0.75, 0.90 or 1.05. They concluded that irrigation at IW:CPE ratios of 0.75 and 0.90 resulted highest grain yield. Looking in to these facts the present study was initiated to find out the suitable irrigation schedule and seed rate for obtaining maximum production of wheat.
Materials and Methods
The experiment was laid out in a randomized complete block design with split-plot arrangement and replicated thrice. During the crop season 1999-2000, wheat (cv. Inqlab-91) was sown in lines, 25-cm apart, with the help of a single-row hand drill at the rate of 100 (S1), 125 (S2) and 150 (S3) kg ha-1 and was subjected to irrigation at IW:CPE ratios of 0.70 (I1), 0.90 (I2), 1.10 (I3) and 1.30 (I4). Irrigation treatments were randomized in main- plots (6 x 6 m2) while seed rates in sub-plots (2 x 6 m2). Pan evaporation was recorded from the pan installed in the observatory at the research area. Pan evaporation for the interval between each irrigation was adjusted using a pan coefficient (on the basis of temperature, humidity and wind velocity in the research area, kp was found to be 0.85) to obtain cumulative pan evaporation (CPE). The desired amount of water according to the treatment was applied using a cut-throat flume (3’ x 8″ size). All other intercultural operations like weeding, hoeing, fertilizer application, etc. were kept uniform. At maturity, data for various agronomic traits viz., plant height, tillers m-2, grains spike-1, 1000-grain weight, grain yield, straw yield and harvest index were collected. Water use efficiency of all the treatments was also calculated. Data were subjected to analysis of variance, according to Steel and Torrie (1984) to sort out significant difference among treatments. LSD test was used to compare treatment means. Trend analysis (Gomes and Gomes, 1983) was also conducted to determine the linear, quadratic or cubic response of crop parameters to irrigation and seed rate treatments.
Results and Discussion
On the basis of cumulative pan evaporation the experiment was irrigated 4 times. The total amount of irrigation water applied to I1, I2, I3 and I4 treatments was 178, 238, 280 and 340 mm, respectively. After subjecting the data to analysis of variance (Table 1) it was revealed that tillers m-2, grains spike-1, 1000-grain weight, grain and straw yield, harvest index and water use efficiency were significantly influenced due to both irrigation as well as seed rate treatments. The interactive effect of irrigation and seed rate was significant in case of grains spike-1 only. Plant height, however, remained unaffected due to any of the experimental treatments. A perusal of (Table 2 ) displayed that number of tillers m-2 were maximum at the highest level of irrigation (I4) and was statistically similar at rest of the three irrigation levels. Similarly, maximum tillers m-2 were recorded with a seed rate of 150 kg ha-1 while at 100 or 125 kg seed rate, the tiller number was reduced. Trend analysis indicated a significant linear response (Fig. 1a and b) of tillers m-2 to both irrigation and seed rate treatments. These results thus, indicate that tiller number m-2 increased with an increase in irrigation amount as well as the seed rate.
| Table 1: | Analysis of variance (including trend analysis) for different plant traits of wheat as affected by different irrigation and seed rate treatments (mean squares) |
| * P≤0.05,** P≤0.01, L= liner trend, Q = Quadratic trend, C= Cubic trend | |
| Table 2: | Mean values of all the traits as affected by irrigation and seed rates and their statistical significance |
| -Means sharing common letter do not differ significantly at 5% probability level using LSD. IW = Irrigation water, CPE = Cumulative Pan Evaporation. | |
That might be due to high plant population at high seed rate. Yoon et al. (1991) also reported that percentage of effective tillers increased with highest sowing rate due to which grain yield also increased. While Lafond (1994) reported that increasing seed rate from 168 to 202 kg ha-1 improved grain yield significantly due to more number of spikes.
On the contrary grains spike¯1 showed an increase up to I3 level of irrigation where they were maximum but reduced in response to further increase in irrigation. The same trend was observed in case of seed rate treatment. Grains spike-1 increased with an increase in seed rate from 100 to 125 kg ha-1 but further increase in seed rate (to 150 kg ha-1) reduced them. Significant quadratic trend (Fig. 2a and b) of grains spike-1 to both irrigation and seed rate treatments also confirmed this fact which indicates the result of competition of plants for more space and nutrients. At highest level of irrigation and seed rate, plant population was also high which created a sort of competition for space and nutrition and out come was a reduction of number of grains spike-1. However, Sharma and Malik (1993) indicated that yield and yield components were unaffected by seeding rates.
The same phenomenon was operative in case of 1000-grain weight where a linear increase in 1000-grain weight was indicated in response to increase in irrigation or seed rate (Fig. 3a and b). However, increase in 1000-grain weight with irrigation from I3 to I4 or seed rate of 125 kg to 150 kg ha-1 was not significant (Table 2). Response of grain yield to irrigation or seed rate was quadratic (Fig. 4a and b). Grain yield increased upto I3 level of irrigation but further increase in response to increase in irrigation (at I4 level) was non-significant (Table 2). Similarly grain yield was maximum with a seed rate of 125 kg ha-1 but further increase in seed rate to 150 kg ha-1 did not increase the grain yield. Straw yield was maximum at I2 level of irrigation and was statistically similar at higher irrigation levels showing a significant cubic response of irrigation treatments (Fig. 5a). However, it displayed a linear increase with increasing seed rate (Fig. 5b). Straw yield was maximum (7.36 t ha-1) with a seed rate of 150 kg ha¯1 but statistically similar to that obtained with 125 kg seed rate (Table 2). On the contrary Paul (1992) stated that sowing rates of 120, 140 and 160 kg ha-1 did not affect significantly grain or straw yield.
A critical perusal of harvest index (Table 2) indicates that it responded inversely showing a significant cubic response to irrigation treatments (Fig. 6a). Maximum value of harvest index was observed at lowest level of irrigation and further increase in irrigation although produced variable response, however, showed a reduction at highest levels of irrigation. Response of harvest index to seed rate was also inverse but linear (Fig. 6b).
| Fig. 1: | Response of number of tillers per m2 to different irrigation (a) and seed rate (b) treatments. |
| Fig. 2: | Response of number of grains spike¯1 to different irrigation (a)and seed rate (b) treatment. |
| Fig. 3: | Response of 1000-grain weight to different irrigation (a) and seed rate (b) treatments. |
| Fig. 4: | Response of grain yield ha-1 to different irrigation (a) and seed rate (b) treatments. |
It decreased by increasing seed rate. Water use efficiency showed a significant reduction with increase in irrigation level. It was maximum at I1 level of irrigation and minimum at I4 level of irrigation showing a linear decrease in WUE in response to irrigation treatments (Fig. 7a). On the contrary this response was significantly quadratic (Fig. 7b) with seed rate treatments. WUE was increased with the increase in seed rate from 100 kg to 125 kg ha-1. But further increase in seed rate to 150 kg ha-1 produced non-significant decrease. The results indicated that wheat was quite responsive to increase in irrigation as well as seed rate. Increase in both treatments resulted an in increase in plant population m-2, which was indicated in terms of tillers m-2.
| Fig. 5: | Response of straw yield ha-1 to different irrigation (a) and seed rate (b) treatments. |
| Fig. 6: | Response of harvest index to different irrigation (a) and seed rate (b) treatments. |
| Fig. 7: | Response of water use efficiency to different irrigation (a) and seed rate (b) treatments. |
On the other hand this increase in plant population also created a sort of competition among plants for space and nutrition. This competition was, however, severe at highest plant population as compared to that at lower population. In other words, highest irrigation and seed rate produced greater plant population m-2 and thus the competition among plants was increased. Result was the reduction in important yield attributes like grains spike-1 and 1000-grain weight, which ultimately produced less grain yield at higher levels of experimental treatments. Thus, it may be inferred that to obtain the maximum production of wheat it should be sown at the rate of 125 kg ha-1 and should be irrigated at IW:CPE ratio of 0.9.