Intensification of Rice Production Through Different Fertilizer Management Approaches Under Variable Irrigation Regimes

Water scarcity is the main problem in boro season in Bangladesh which limits growth and development of crop plants especially in rice. The field experiment was carried out at the Soil Science Field Laboratory of Bangladesh Agricultural University. The experiment was laid out in a split plot design with three replications. BRRI dhan29 was used as a test crop. Treatments were the combination of water saving techniques and different nutrients of organic and inorganic approaches. There were four types of water management viz. I1: minimum irrigation, I2: normal irrigation, I3: continuous flooding and I4: alternate wetting and drying (AWD). On the other hand five fertilizers management approaches viz. F1: 100% recommended fertilizer dose (RFD) chemical fertilizers (NPKSZn), F2: 75% RFD chemical fertilizers (NPKSZn) + 5 t ha cowdung, F3: 75% RFD chemical fertilizers (NPKSZn) + 5 t ha cowdung slurry, F4: 75% RFD chemical fertilizers (NPKSZn) + 3 t ha poultry manure and F5: 75% RFD chemical fertilizers (NPKSZn) + 3 t ha poultry manure slurry were tested. The water management practices were placed in the main plot and fertilizer management practices were given in the sub plots. Results revealed that minimum irrigation caused significant reductions in growth and yield of BRRI dhan29. On the other hand, AWD technique did not reduce the growth and yield of BRRI dhan29 in comparison to continuous flooding. It was also revealed that plant height, panicle length, number of effective tillers per hill and grains per panicle were significantly increased in I3F3 (continuous flooding with 75% RFD chemical fertilizers + 5 t ha cowdung slurry) treatment compared to other treatments. The highest grain and straw yields were obtained from I3F3 treatment. Nutrient uptake by BRRI dhan29 responded significantly in I3F3 treatment which was statistically similar to I3F4, I4F5, I2F5, I4F4 and I4F3 treatments. Finally it can be concluded that application of continuous flooding or AWD with 75% RFD chemical fertilizers + 5 t ha cowdung slurry showed better performance than other treatments for maintaining better rice production. Article history Received: 18 Oct 2020 Accepted: 14 Mar 2021 Published: 30 Mar 2021


Introduction
Rice (Oryza sativa L.) is the staple food for the people of Bangladesh. Bangladesh ranks 4 th position in rice production among rice growing countries of the world (FAO, 2018). Rice is intensively cultivated in 28.46 million acre land in Bangladesh (BBS, 2019). Integrated use of organic manure and chemical fertilizers with proper irrigation would be quite promising not only in providing greater stability in production, but also in maintaining better soil fertility. Global agriculture faces two major challenges. Food production needs to increase to feed a still-growing world population and this increase needs to be accomplished under increasing scarcity of water resources (Yang et al., 2007). Different developmental stages of rice are known to respond differently to different irrigation regimes. Rice plant shows a variety of adaptive mechanisms to respond to water deficit conditions. Water stress decreases relative water contents, water potential, growth and yield of various crops (Bakul et al., 2009;Akram, 2011). By 2025, it is necessary to produce about 60% more rice than is currently being produced to meet the food needs of a growing world population (Nhamo et al., 2014). Rice is the greatest consumer of water among all crops and consumes about 80% of the total fresh water resources. Meanwhile, resource for irrigation has declined gradually over the past decades due to rapid urbanization and industrialization which exacerbates the problem of water scarcity (Belder et al., 2004). Rice crop is very sensitive to water stress. Attempts to reduce water in rice production may result in yield reduction (Vijay, 2018). The challenge is to develop economically and environmentally sustainable rice-rice cropping system that allows rice production to be maintained or increased in the face of declining water availability (Ullah et al., 2017).
Development of a sustainable intensive agriculture is essential for crop production, providing conservation of environment including soil and water (Athar and Ashraf, 2005). A strategy of integrated plant nutrient management is crucial to maintain soil fertility as well as to increase crop productivity. In addition to use of inorganic sources of plant nutrients, organic sources need to be considered to prevent nutrient mining, maintaining soil fertility and increasing crop production (Dass et al., 2017). Cowdung, poultry manure and their bio-slurries are the good sources of organic matter in soils (Malika et al., 2015). Integrated use of inorganic fertilizers with organic manures not only sustains the crop production but also is effective in improving soil health and enhancing nutrient use efficiency (Ali et al., 2009). Drought in north-western Bangladesh in recent decades had led to a shortfall of rice production of 3.5 million tons (BARC, 2012). Several strategies have been proposed to improve the productivity of rice under water deficit condition. Conservation tillage, mulching and irrigation scheduling are useful strategies to reduce the excess use of water and increase crop yield. Furthermore, integrated plant nutrient system has gained considerable attention in mitigating the adverse effects of various stresses including water stress.
Keeping in view the considerable demand for food, improvement in rice production under water deficit condition is prime importance. Therefore, this research was undertaken to study the possible roles of water and nutrient management in improving yield of rice under different irrigation regimes. The main purpose of this research was to improve rice production under different irrigation regimes through proper management of fertilizers.

Materials and Methods
The experiment was conducted at Soil Science Field Laboratory of BAU during boro season (2015-16). The experimental soil belongs to Sonatola series under the AEZ of Old Brahmaputra Floodplain. BRRI dhan29 was used as a test crop. Fourty-days-old rice seedlings were transplanted in the experimental fields at a spacing of 20 cm × 20 cm. The experiment was laid out in a split plot design where the experimental area was divided into 3 replications. Each block was divided into 20 unit plots with raised bunds as treatments. Thus total number of unit plots was 60. The unit plot size was 3m x 2m and plots were separated from each other by ails (20 cm). One meter drain was separated unit block from one another. Two types of treatments were used in this experiment, irrigation regimes were assigned in main plots and nutrient management were placed in subplots. There were four types of water management viz. I1: minimum irrigation, I2: normal irrigation, I3: continuous flooding and I4: alternate wetting and drying (AWD). On the other hand five fertilizers management approaches viz. F1: 100% recommended fertilizer dose (RFD) chemical fertilizers (NPKSZn), F2: 75% RFD chemical fertilizers (NPKSZn) + 5 t ha -1 cowdung, F3: 75% RFD chemical fertilizers (NPKSZn) + 5 t ha -1 cowdung slurry, F4: 75% RFD chemical fertilizers (NPKSZn) + 3 t ha -1 poultry manure and F5: 75% RFD chemical fertilizers (NPKSZn) + 3 t ha -1 poultry manure slurry were tested.
Fertilizer N, P, K, S and Zn from urea, triple superphosphate, muriate of potash, gypsum and zinc sulphate, respectively were applied to the experimental plots. Triple superphosphate, muriate of potash, gypsum and zinc sulphate were applied during final land preparation to the experimental plots as per treatments. Urea was applied in three equal splits. Well decomposed cowdung, cowdung slurry, poultry manure and poultry slurry were incorporated in the plots as per treatment at 7 days before transplanting. Cowdung, cowdung slurry, poultry manure and poultry slurry were mixed thoroughly with the soil at the time of final land preparation. The crops were harvested at full maturity. Different plant parameters including grain and straw yields were recorded after harvesting. The crop was harvested at full maturity. One m 2 of each plot was harvested, bundled separately and brought to the threshing floor. Then the harvested crop was threshed. Grain and straw yields were recorded and moisture percentage was calculated after drying in the oven. The grain and straw yields were adjusted on 14% moisture. Five hills were randomly selected from each plot at maturity to record the yield contributing characters. Grain and straw samples were kept for chemical analyses. The plant height was measured from the ground level to the top of the panicle. From each plot, plants of 5 hills were measured and averaged. The measurement of panicle length was taken from basal node of the rachis to apex of each panicle. Each observation was an average of 5 hills.
Five hills were taken randomly from each plot and total numbers of effective tillers hill -1 were recorded. Five panicles were taken at random hill -1 and the filled and unfilled grains panicle -1 were counted and averaged. 1000-grain was taken from the collected samples treatment wise and the weight was recorded after sun drying in an electrical balance. Grain and straw yields of BRRI dhan29 were recorded from each plot after drying and weighing carefully.
The yields were expressed as kg ha -1 on 14% moisture basis. Initial soil samples were collected at a depth of 0-15 cm from the surface. After removing weeds, plant roots, stubbles, stones, etc, the samples were air dried and ground to pass through a 2 mm (10 meshe) sieve. Plant samples were analyzed for N, P, K and S contents following semi-micro Kjeldahl method, Olsen method, Ammonium-acetate extraction method and Calcium chloride extraction method respectively in the Department of Soil Science of BAU. Data were analyzed statistically by ANOVA. The significance of differences between mean values was evaluated by Duncan's Multiple Range Test using software package, Stats

Effects of irrigation and fertilizers on the yield components of rice
Irrigation and fertilizers resulted in significant increases in plant height and other attributes of BRRI dhan29. Combined application of N, P, K, S and Zn fertilizers significantly influenced the plant height, number of effective tillers panicle length, and number of grains per panicle of BRRI dhan29 under different irrigation regimes. The maximum plant height (92 cm) was obtained in treatment I3F3 (continuous flooding with 75% RFD chemical fertilizers + 5 t ha -1 cowdung slurry) which was statistically similar with the treatments I3F2 and I3F4. The lowest plant height (78 cm) was observed in I1F1 treatment which was statistically similar with treatments I1F2, I1F3, I1F4 and I1F5 (Table 1). The maximum number of effective tillers per hill (13.50) was obtained from treatments I2F4, I3F3 and I3F5 which was at par with I3F2 and I3F4. The lowest effective tiller hill -1 was (9.40) was found in I1F1 which was statistically similar with treatments I1F2, I1F3, I1F4 and I1F5 (Table 1). The maximum filled grains panicle -1 (133) were found in treatment I3F5 (continuous flooding with 75% RFD chemical fertilizers + 3 tha -1 poultry manure slurry) which were statistically similar to treatments I3F2, I4F2, I4F3, I4F4, I4F5, I3F3, I3F4, I2F3 and I2F4. The lowest grains panicle -1 (94) was obtained in treatment I1F1 (Table 1). Combined effect of irrigation and fertilizers had no significant difference in 1000-grain weight ( Table 1).

Effects of irrigation and fertilizer management on the yield of rice
Significant variation in grain yield of BRRI dhan29 was observed due to application of irrigation and fertilizers ( Figure 1). Application of irrigation significantly increased grain yield in rice. In combined effect of irrigation and fertilizers, the maximum grain yield was obtained from treatments I3F4, I3F3 and I4F4 (5.49 tha -1 ) which were statistically similar with treatments I4F2, I4F3, I4F5 and I3F2. The lowest yield was obtained from I1F1 (minimum irrigation with 100% RFD chemical fertilizers-NPKSZn) treatment (4.32 tha -1 ) which was statistically different from other treatments (Figure 1). A significant variation in straw yield of rice was also observed due to combined application of irrigation, fertilizers and manures.  In combined effect of irrigation and fertilizers, the maximum yield of straw (6.35 t ha -1 ) was obtained from treatment I3F4 (continuous flooding with 75% RFD chemical fertilizers + 3 t ha -1 poultry manure) which was statistically similar with treatments I3F3, I3F2, I3F5, I4F4 and I4F5 whereas the lowest yield of straw (5.35 tha -1 ) was obtained from the treatment I1F1 (minimum irrigation with 100% RFD chemical fertilizers-N,P,K,S,Zn) which was statistically similar with treatments I1F2, I1F3 and I1F4 but statistically different from other treatments (Figure 1).

Nutrient uptake by rice plant due to irrigation and fertilizer management
Nitrogen uptake A significant variation in nitrogen uptake by grain and straw was observed due to application of irrigation and fertilizers. The highest N uptake (66.98 kg ha -1 ) by grain was obtained in treatment I2F5 which was statistically different from other treatments. The lowest N uptake (45.96 kg ha -1 ) by grain was observed in treatment I1F1 which was statistically similar to I1F2, I1F3 and I2F1 ( Table  2). The N uptake by straw ranged from 14.98 to 19.62 kg ha -1 . The highest N uptake by straw was obtained from treatment I3F5 which was statistically similar to treatments I3F3, I3F4, I4F4 and I4F5. The lowest N uptake by straw was found in treatment I1F1 which was statistically similar to I1F2 and I1F4 (Table 2). Total N uptake by BRRI dhan29 ranged from 60.94 to 85.40 kg ha -1 ( Table 2). The highest total N uptake was recorded in treatment I2F5 (normal irrigation with 75% RFD chemical fertilizers + 3 t ha -1 poultry manure slurry) which was statistically different from other treatments. The lowest total N uptake was found in I1F1 which was statistically similar to I1F2, I1F3 and I2F1 ( Table 2). The result showed that the total N uptake both by grain and straw were more prominent due to combined application of irrigation and fertilizers.

Phosphorus uptake
Results in Table 2 demonstrate that phosphorus uptake by grain and straw differed significantly due to different treatments. The highest P uptake (11.45 kg ha -1 ) by grain was obtained in treatment I4F4, which was statistically similar to I4F5 and I3F3. The lowest uptake of P (8.240 kg ha -1 ) by grain was obtained in treatment I1F1 which was statistically similar to I1F2 ( Table 2). The highest P uptake (8.64 kg ha -1 ) by straw was obtained in treatment I3F4 (continuous flooding with 75% RFD chemical fertilizers + 3 t ha -1 poultry manure) which was statistically similar to I4F4 and the lowest uptake (5.28 kg ha -1 ) was found in I1F1 which was statistically similar to I1F2, I1F3, I1F4 and I2F1 (Table 2). Total P uptake by BRRI dhan29 ranged from 13.56 kg ha -1 to 19.89 kg ha -1 ( Table 2). The highest total P uptake (19.89 kg ha -1 ) was recorded in the treatment I3F4 (continuous flooding with 75% RFD chemical fertilizers + 3 t ha -1 poultry manure) which was statistically different from other treatments. The lowest total P uptake (13.56 kg ha -1 ) was found in I1F1 which was statistically similar to I1F2 (Table 2).

Potassium uptake
Irrigation and fertilizers influenced the K uptake by BRRI dhan29 (Table 3). The highest K uptake (19.17 kg ha -1 ) by grain was obtained in treatment I3F4 which was statistically similar to I4F4. The lowest uptake of K (9.80 kgha -1 ) by grain was obtained in treatment I1F1 which was statistically similar to I1F2 and I2F1. The highest K uptake (90.55 kg ha -1 ) by straw was obtained in treatment I4F5 and the lowest uptake (51.32 kg ha -1 ) was found in I1F1. Total K uptake by BRRI dhan29 ranged from 61.03 kg ha -1 to 107.1 kg ha -1 (Table 3). The highest uptake (107.1 kg ha -1 ) was found in treatment I4F5 (AWD with 75% RFD chemical fertilizers + 3 t ha -1 poultry manure slurry) with which was statistically similar to I3F4 and I3F5. The lowest uptake (61.03 kg ha -1 ) was found in I1F1 which was statistically different from others (Table 3). Results shown in (Table 3) indicate that S uptake by BRRI dhan29 was influenced significantly due to application of irrigation and fertilization. The highest S uptake (11.35 kg ha -1 ) by grain was obtained in treatment I3F3 which was statistically similar to I3F4, I3F2 and I3F5. The lowest uptake of K (7.75 kg ha -1 ) by grain was obtained in treatment I1F1. The highest S uptake (11.34 kg ha -1 ) by straw was obtained in treatment I3F3 and the lowest uptake (8.86 kg ha -1 ) occurred in I1F1 which was statistically similar to I1F2, I1F3 and I1F4. Total S uptake by BRRI dhan29 ranged from 16.61 kg ha -1 to 22.7 kg ha -1 (Table 3). The highest uptake (22.7 kg ha -1 ) was found in treatment I3F3 (continuous flooding with 75% RFD chemical fertilizers + 5 tha -1 cowdung slurry) which was statistically similar to I3F2, I3F4 and I3F5. The lowest uptake (16.61 kg ha -1 ) was found in I1F1 (Table 3).

Discussion
Irrigation and fertilizers had great influences on growth and yield performance of rice. Continuous flooding as well as AWD increased the yield contributing characters and nutrient uptake of BRRI dhan29. Akram (2011) experiment showed that the sensitivity of rice to water stress and changes in water relations and yield of rice under water stress conditions applied at different growth stages. The results indicated that high value of relative water contents was associated with increased yield and yield components. This would help stabilize the crop production, and significantly contribute to food and nutritional security in developing countries and semiarid tropical regions. In this study, AWD has been reported to save water compared with continuous flooding (CF) in rice cultivation which is supported by Belder et al. (2004). Yang et al. (2007) reported that conventional irrigation where drainage was in midseason and flooded at other times, the water-saving irrigation increased grain yield by 7.4% to 11.3%, reduced irrigation water by 24.5% to 29.2%, and increased water productivity (grain yield per cubic meter of irrigation water) by 43.1% to 50.3%. Balasubramanian and Krishnarajan (2001) inferred that AWD treatment would be the best choice for the water saving (11.3%) and the highest rice yield in silty loam soil, which is very pertinent with this experiment. Chapagain and Yamaji (2010) showed that the 8 days drying period gave the highest yield of 7.13 t ha -1 compared with the conventional method of growing rice which gave a yield of 4.87 t ha -1 which is similar with the treatment of I4F5 in this study. This was an increase of 46.4% above the conventional method of growing rice. Water saving associated with this drying regime was 32.4%. Zaman (2002) showed that timely irrigation in rice field increased the availability of nutrients in rice plant which was in agreement with Devi et al. (2012).
From above discussion it can be said that AWD and continuous flooding seems to be good for BRRI dhan29. Garg et al. (2005) reported that the bio-slurry is a good source of plant nutrients and can improve soil properties compared with general chemical fertilizer, and can reduce the use of chemical fertilizers. Application of bioslurry (cow dung slurry and poultry manure slurry) would help build up organic matter in soil through minimizing carbon losses as CO2. The integrated treatments produced significantly higher grain and straw yields compared to the absolute chemical fertilizer treatments. Ali et al. (2009) reported that the integrated use of fertilizers and manure resulted in considerable improvement in soil health by increasing organic matter, available P, and S contents of soils. Abubaker (2012) showed that biogas residues increased crop yield to the same extent or more than conventional mineral fertilizer and compost. Akter (2011) and Malika (2011) who observed positive effects on S uptake by rice with application of manures and fertilizers that is showed in my treatment I3F3 (Continuous flooding with 75% RFD chemical fertilizers (NPKSZn) + 5 t ha -1 cowdung slurry). Malika et al. (2015) evaluation showed the combined effect of organic and inorganic fertilizers on the growth and yield of rice (BINA dhan-7). Mazumder et al. (2005) reported that different levels of nitrogen influenced grain and straw yields with the application of 100% RD of N (99.82 kg N ha -1 ). Munira's (2014) experiment on T. Aman rice (cv. BINA dhan-7) showed that application of chemical fertilizers in combination with poultry manure based on IPNS could be recommended for BINA dhan-7 production in aman season. Islam et al. (2014) found that combined effect of manures and fertilizers increased the yield of BRRI dhan49. Sarker (2013) experiment showed that the performance of bio-slurry on tomato production, the use of poultry bio-slurry not only gives higher yield but also improves soil health which is necessary for sustainable crop production by maintaining soil fertility and productivity. The overall findings of the study indicate that the integrated use of chemical fertilizer and manure is important for sustainable crop yield in a rice-rice cropping pattern. Here all the treatments, bio-slurry (CD slurry and PM slurry) combined with chemical fertilizer had performed better than other treatments. In this context we can say that continuous flooding or AWD with 75% RFD chemical fertilizers and 5 t ha -1 cowdung increases grain yield, straw yield and other parameters.

Conclusion
Combined application of irrigation with organic manures, bio-slurries and chemical fertilizers had significant effects on yield and yield contributing characteristics of BRRI dhan29. Nutrient uptake by rice crop was also significantly affected due to application of manure or bio-slurry with fertilizers and irrigation. It can be concluded that combined application of irrigation and manure or bio-slurry with fertilizer increased crop production. Application of continuous flooding or AWD with 75% RFD chemical fertilizers + 5 t ha -1 cowdung slurry showed better performance than other treatments for BRRI dhan29 maintaining better rice productivity.