Effect of rice stubble and irrigation scheduling on water use efficiency (WUE) and water productivity of wheat

Introduction

Wheat is not only a major food source, but it is also an important crop for national food security, as it significantly contributes to food grain buffer stock. It plays an important role in ensuring national food grain adequacy, which has stabilised the country's food grain production at increasing levels. After rice, wheat is India's second most important food crop, covering 31. 4 Mha with a production of 107.6 mmt and a productivity of 3.42 tha -1 (Department of Agriculture, 2019-20) [5] . In many parts of the world where rainfall is insufficient to meet crop demand, water has always been the primary limiting factor for crop production. Because of the rising competition for insufficient water resources all over the world, as well as the progressively rising demand for agricultural commodities, there has never been a better time to improve agricultural water use's effectiveness and productivity. Agriculture productivity is critical and water productivity serves as a key indicator in agriculture for assessing the impact of irrigation scheduling decisions on water management. Water productivity can be used to quantify the impact of irrigation scheduling decisions. Irrigation is one of the most important and costly inputs directly impacting wheat growth and yield, when applied at the right time and in the right quantity, irrigation can significantly increase yield by creating a favourable soil moisture regime. The degree, duration and timing of the imposed soil-moisture deficit under limited irrigation determine the extent of grain yield reduction. The procedure for determining irrigation scheduling refers when and what amount of water should be applied per irrigation. Proper scheduling of irrigation is critical to maximizing the efficiency of water, energy, and other production inputs. Three significant factors influence scheduling of irrigation: (a) Crop water requirements; (b) Irrigation water availability; and (c) Water in the root system storage capacity. Crop water requirements are crucial for determining the timing of irrigation throughout the crop-growing season in irrigation projects.

Currently, crop residue burning is a major issue in India. Rice stubble or straw burning is a widespread issue in North India, causing severe pollution levels in Delhi and its surrounding areas. The nutrients in the stubble are destroyed during the burning process. As a result, proper crop residue management is essential. The removal of these crop residues reduces soil fertility and thus crop production. Most crop straw or stubble contains approximately 35%, 10%, and 80% of total N, P, and K respectively taken up by plants ( Barnard and Kristofferson, 1985) [4] . According to the Department of Agriculture, Punjab government, less than 1% of farmers incorporate crop stubble because it requires more tillage operations. Cultivation on rice stubble will allow farmers to plan water rotation between fields, thereby minimizing crop water stress. Cutting rice stubble at various heights allows the remaining crop residues on the field to help replenish soil moisture. The current study aims to observe irrigation treatments at various stages of wheat growth.

Materials and Methods

During the Rabi season, an experimental trial was carried out at Dr. Rajendra Prasad Central Agricultural University's research farm at Pusa (Samastipur), Bihar to investigate the effect of rice stubble and irrigation scheduling on WUE and water productivity of wheat. The research field is located on the Burhi Gandak River's southern bank. The research field was connected to the main irrigation channel, which, in turn, was linked to the farm tube well to ensure consistent and timely irrigation. Throughout the study, drainage system was in place to remove excess water. The trial was carried out in a calcareous sandy loam soil, classified under the soil order entisol. The soil testing results indicated an alkaline type of soil reaction (8. of wheat was 120:60:40 kg/ha N: P: K respectively. The spacing was maintained at 20 cm (RxR). Line sowing was done by manual broadcasting followed by mixing with a rotavator according to the treatment. Wheat was sown on 2 nd December 2021. Nitrogen (N) dose was applied in two splits; half at planting time as basal and the other remaining half at two days later as top dressing. The entire amount of P and K was applied as basal at the time of sowing. Pre-sowing irrigation was applied for both seasons during 2021-2022. Common irrigation as per crop needs was applied based on moisture requirement status and crop development stages. The other management practices were adopted as per package of practices. Rice stubbles were cut at different heights i.e. 5, 20 and 35 cm from 25 th to 30 th November, 2021. During the trial, meteorological data were normal for crop growth. Observations on the WUE and water productivity data were assessed. The statistical analysis was carried out as per Gomez and Gomez (1984) [6] . Each irrigation applied 6 cm of water to the field. Treatment I 1 received (6 cm irrigation + 2.94 cm rain = 8.94 cm), I 2 (12 cm irrigation + 2.94 cm rain = 14.94 cm), I 3 (18 cm irrigation + 2.94 cm rain =14.94 cm), I 4 (18 cm irrigation + 2.94 cm rain =20.94 cm) and I 5 (24 cm irrigation + 2.94 cm rain = 26.94 cm).

Water Use Efficiency (WUE)

It denotes the amount of marketable product (grain) obtained per unit of crop water applied. It is calculated by using the formula below:-

Water productivity was determined and expressed in m 3 for each irrigation treatment. The following formula is used to calculate water productivity:-

Results and Discussion

Soil moisture Content

Soil moisture content before and after irrigation at 5-day interval up to second irrigation, depending upon the growth stages of crop in different irrigation level and rice stubble height is presented in table 1. The treatment I 5 showed highest soil moisture 5-days after each of the three irrigations followed by I 4 . In the case of replication, R 3 showed highest soil moisture both before (24.79%) and after (26.55%) irrigation. Hence, it can be concluded that three irrigation in wheat at CRI + maximum tillering + flowering + dough stages retains maximum moisture in soil. This might be due the fact that under lower irrigation level i.e. at I 1, water was used only once. The increase in yield was relatively lesser than increase in water requirement, which consequently decreased WUE under higher number of irrigations. WUE decreased with increasing the irrigation levels. These findings are consistent with those of Kumar and Prasad (1986) [10] , Lal (1984) [11] , Saren et al. (2004) [14] and Bandopadhyay and Mallick (2003) [3] and Kumar and Kumar (2012) [9] .

Effect of rice stubbles on WUE

Citation of data in table 2 regarding WUE revealed that rice stubbles cut at different height treatments showed variation and exerted significant effect on WUE (234.78kg/ha-cm) was maximum at R 2 (Rice Stubble cut at height 20 cm), which was significantly superior to R 3 (Rice Stubble cut at height 35 cm) but was statistically at par with R 1 (Rice Stubble cut at height 5 cm) i.e.220.96 kg/ha-cm (Fig 1). The interaction effect between two treatments i.e. irrigation scheduling and rice stubbles was found to be non-significant at p<0.05. This might be due to reduction in evaporation and increase in WUE and also yield under R 2 was superior over R 3 . The findings were consistent with those of Jack et al. (2010) [7] and Ashworth and McHugh (2010) [2] .

Effect of irrigation scheduling on water productivity

Water productivity under different treatments was computed using net return obtained and water used in different stages of wheat growth and under the crops sown on rice stubbles. [1] reported decrease in water productivity with increase in irrigation level.

Effect of rice stubbles on water productivity

Citation of data in table 2 regarding water productivity revealed that rice stubbles cut at different height treatments showed variation and exerted significant effect on water productivity (0.44 ₹/m 3 ) was maximum at R 2 (Rice Stubble cut at height 20 cm) which was significantly (p<0.05) superior to R 3 (Rice Stubble cut at height 35 cm) but was statistically at par with R 1 (Rice Stubble cut at height 5 cm), which had a water productivity of 0.39 ₹/m³ (Fig 2). The interaction effect between two treatments i.e. irrigation scheduling and rice stubbles was found to be non-significant at p<0.05. This result aligns with the findings of Kumar et al. (2016) [8] . Noellemeyer et al. (2013) [13] and Memon et al. (2013) [12] , who observed higher water productivity under zero tillage compared to conventional tillage.

Conclusion

Considering the limitation of this investigation being conducted at a single site, the following broad conclusions can be drawn from one season. Water use efficiency and productivity were found to be highest in the case of I 1 (irrigation at the CRI stage), which was highly significant under the irrigation scheduling treatment tested. The replication R 2 (Rice stubble cut at 20 cm height) in the sub-plot showed best result among all the three replication for both water use efficiency and water productivity.

References

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