Mahmud Hossain

Organic matter (OM) shows a critical role in mobilization and uptake of arsenic (As) by rice, and water management practice can mitigate this problem. However, very few research highlighted the impact of management of water on rice as influenced by OM amendment. Therefore, this study has evaluated the changes in As mobilization in paddy soil under different OM amendment and water management practices. Here, rice was grown to maturity in a two-factorial pot experiment comprising two different water management practices [continuous flooding (CF) and alternate wetting drying (AWD)] and eight combinations of As and OM amendment [comprising two As treatments (0 and 20 ppm) and four OM amendments (0, 0.25%, 0.5% and 5.0% w/w)]. Application of OM in As contaminated soil caused a significant increase in As accumulation in rice, and exhibited decreased growth and yield of rice. However, the results showed that rice growth and yield was significantly higher under AWD practice compared to CF. Arsenic concentration in rice was the lowest in As and OM control pots (44.67 µg/kg in AWD and 62.13 µg/kg in CF), and higher in As treated pots. Moreover, As concentration in rice grain increased with increasing levels of OM amendment. The As concentration in rice grain (168.44 µg/kg in AWD and 183.85 µg/kg in CF) was significantly higher in As treated pots with 0.5% OM amendment compared to other treatment combinations. Application of 5% OM in As contaminated soil did not produce any grains due to extreme toxicity. Thus, As accumulation in rice can be decreased by AWD water management technique without compromising yield. The findings suggest that applying OM in paddy soils with high soil As content should be done with caution.

One of the primary abiotic factors limiting rice production is zinc (Zn) deficiency. Effective management of Zn in rice soils is crucial, as rice is a staple crop for many nations. To address this issue, a pot trial was conducted at the net house of the Department of Agronomy, Bangladesh Agricultural University, Mymensingh,from December 2019 to May 2020. The trail aimed to assess the impact of zinc on yield performance and grain zinc content of rice. The experiment employed a completely randomized design (CRD) with three replications, involving the applications of six different rates of Zn to three distinct varieties of boro rice. The result revealed that BRRI dhan28 exhibited superior yield and yield-related traits when treated with 12 kg Zn ha-1. Meanwhile, the application of 10 kg Zn ha-1 resulted in the highest Zn content in the grain of BRRI dhan74, considering the quantity of Zn accumulated by the grain. Based on the findings of the study, it can be concluded that applying 12 kg of Zn ha-1 is likely the optimal Zn management strategy to achieve outstanding performance in the rice cultivar BRRI dhan28. Furthermore, applying 10 kg of Zn ha-1 may enhance the Zn content of the grain in BRRI dhan74.

Here is presented a study to investigate the geographic variation in rice grain nutrients (trace and macro-elements and vitamins) and toxicants (arsenic species and cadmium) across a contiguous strip of 36 districts that constitute western Bangladesh. The survey collected ~ 500 market rice samples, averaging 15 samples and 10.7 cultivars per district. New LC-MS methods were developed for rice relevant, B and E complex compounds. Cadmium and zinc decreased southward, while copper, DMA, inorganic arsenic and oryzanols decreased northwards. There was a longitudinal gradient for iron, potassium, and vitamin B6. The greatest changes ~ twofold for cadmium and vitamin B6, and 1.5 for zinc across these gradients. The gradients may be driven by climate, geographical setting, soils, or cultivar, or a combination of all. The most obvious gradient was the transition from high to low altitude and from Pleistocene to Holocene soils as land transitioned from the upland plains of the north to sea-level in the south. Rice is a very important source of copper, phosphorus, vitamin B1, and zinc, and to a lesser extent iron, B3, B6, potassium. It is a poor source of vitamin E and calcium.

Water-saving irrigation occasionally causes an inconsequential yield loss in rice; thereby, biochar incorporation in this context has great scope due to its properties, including the release of nutrients and improving soil physicochemical properties. An experiment was conducted to investigate the effect of biochar combined with fertilizer on physiological response, water and nutrient efficiency of rice and changes in biochemical properties of soil under AWD (alternate wetting and drying) irrigation system. Two types of irrigation practice, such as AWD and CF (continuous flooding), and four types of fertilizer combination, namely T1: 25% Rice husk biochar (RHB) + 75% of recommended fertilizer dose (RFD); T2: 25% oil palm empty fruit bunch biochar (EFBB) + 75% of RFD; T3: 100% RFD; and T0: 0% biochar and fertilizer, were assigned to assess their impacts. The AWD irrigation produced a sharply reduced grain yield (210.58 g pot⁻¹) compared to CF irrigation (218.04 g pot⁻¹), whereas the biochar combination treatments T1 and T2 produced greater yields (260.27 and 252.12 g pot⁻¹, respectively), which were up to 12.5% higher than RFD. Within AWD, irrigation water usage by T1 and T2 (98.50 and 102.37 g L⁻¹, respectively) was profoundly reduced by up to 28.8%, with improved water use efficiency (WUE). The main effect of biochar treatment T1 and T2 also increased photosynthesis rate during vegetative and maturing stage (up to 17.6 and 24.4%, respectively), in addition to boosting agronomic efficiency of nitrogen (N), phosphorous (P) and potassium (K) compared to RFD (T3). Nevertheless, T1 and T2 significantly enhanced the total carbon and nitrogen; dehydrogenase and urease enzyme activities also increased in both irrigation regimes. The results reveal that the integrated application of RHB and EFBB with fertilizer in the AWD regime significantly reduces irrigation water usage and improves nutrient use efficiency, WUE and soil biochemical properties with a minimum yield penalty for rice.

Biochar is a potential carbon-rich soil amendment that improves the physicochemical properties of soil, besides acting as a controlled release fertilizer. An experiment was conducted to investigate the effect of biochars on rice yield, fertilizer use efficiency and recovery under water-saving irrigation by ¹⁵N isotopic tracer study. Two types of irrigation as alternate wetting and drying (AWD) and continuous flooding (CF), and four types of biochar treatments such as rice husk biochar (RHB) with ¹⁵N urea, oil palm empty fruit bunch biochar (EFBB) with ¹⁵N urea, ¹⁵N urea alone and control, were applied to assess their impact on rice. About 4% reduced grain yield with 18% improved water productivity was achieved by the AWD regime over the CF, whereas RHB and EFBB significantly increased rice yield compared to unamended soil. RHB and EFBB enhanced the water productivity up to 25.3%. The fertilizer N uptake and recovery were boosted by RHB and EFBB up to 18.8% and 24.5%, respectively. RHB and EFBB accelerated the agronomic use efficiency and partial factor productivity of N (up to 21% and 8%, respectively). RHB and EFBB profoundly enhanced the pH, the total C and N and the available N (NH₄⁺ and NO₃⁻) of the post-harvest soil. This study suggests that adding RHB and EFBB with urea improves fertilizer N utilization and soil N retention, and their combination with AWD could enhance rice yield with better water productivity due to their porous structure and controlled N release capacity.

The critical limit for zinc (Zn) varies from 0.38 to 2 µg/g soil depending on the crop and soil type. However, the critical limit for Zn was not explored recently for rice and potato cultivation in the floodplain soils of Bangladesh. A pot experiment was conducted to determine the critical limits of Zn in soil and plants for rice and potato cultivation in two agro-ecological zones (AEZs) of Bangladesh. The soil samples were collected from 20 different locations of Old Brahmaputra and Active Ganges Floodplains with low (1.80 µg/g) Zn status. The experiment was laid out in a factorial and completely randomized design with two levels of Zn (Zn₀ and Zn₁ (0 and 4.87 kg/ha as Zn sulphate)) applied to 20 different soil samples for rice and potato cultivation using three replications. The critical limit of Zn was determined through a graphical and statistical approach and crops were harvested at the stem elongation (for rice) and tuber filling (for potato) stage. The critical limit of Zn in soil for rice was found to be 0.8 and 0.85 µg/g by graphical and statistical methods, respectively, and both methods revealed the same value (0.73 µg/g) for potato. The critical limit of Zn in rice plants was 23.9 and 24.32 µg/g, whereas in potato plants it was 27.1 and 26.61 µg/g, determined by graphical and statistical methods, respectively. The added Zn supply in soil significantly increased the dry matter accumulation in rice (by 5.6%) and potato (by 10%) compared to no Zn supply. Therefore, a significant positive response to added Zn could be observed on crop growth and yield when the Zn concentration remained below the mentioned critical level for rice and potato cultivation in floodplain soils of Bangladesh.

Globally, the risk of arsenic (As) contamination in soil and rice is well documented across the globe. In Bangladesh, drinking water and rice are two major exposure pathways of As to humans. Therefore, the efficiency of recent technologies to reduce rice As and associated human health risks still need to be deeply investigated. In this direction, a pot experiment was performed to investigate the impact of soil As and agronomic irrigation management on rice (cv. BRRI dhan28) growth, yield, As accumulation, and finally, health risks to humans from consuming rice. Treatment combinations were made with three levels of As (0, 20, and 40 mg kg⁻¹) having two irrigation procedures, including alternate wetting and drying (AWD) and traditional continuous flooding (CF). According to the findings, As pollution in the soil lowered the yield contributing features and rice yield, including panicle length, filled grains per panicle, sterile grains per panicle, 1000-grain weight, grain yield, and straw yield. AWD water management significantly improved the growth performance and productivity of rice. Grain yield was increased by 13% in AWD compared to CF. Rice grain and straw As concentrations were increased to 0.56 mg kg⁻¹ and 15.10 mg kg⁻¹, respectively, in soil with 40 mg kg⁻¹ As and CF water management. AWD treatment significantly reduced grain and straw As contents by 16% and 28%, respectively. Increased grain, straw, and total As uptake was noticed with higher soil As concentrations. The study also found that rising soil As raised non-carcinogenic risks (HQ > 1) and carcinogenic risks (CR > 1.010–4) while AWD lowered health risks compared to CF. Thus, rice farming using AWD irrigation could be a viable and long-term solution for reducing As contamination in rice and associated human health hazards.

Rice is a staple food for humans and a key source of soil arsenic (As) transfer to the human food chain. As a result, it is critical to develop ways for reducing As accumulation in rice. A pot experiment with seven different water management practices was done to examine the impacts of water management on rice (cv. BRRI dhan28) growth, yield, and As accumulation in rice grain. Any health risk due to As accumulation in rice grain was also determined. The soil used in the experiment was artificially contaminated with As and the source of As was sodium arsenate (Na₂HAsO₄ 7H₂O). Water management practices affect different plant growth and yield parameters including filled grains per panicle, unfilled grains per panicle, 1000-grain weight, grain yield and straw yield of rice. The number of filled grains per panicle and 1000-grain weight were found to be at their highest in the T₇ (alternate wetting and drying) condition, whereas the number of unfilled grains per panicle was at its lowest in the same treatment. The T₇ also demonstrated the highest grain yield (21.08 g/pot) and straw yield (22.02 g/pot), whereas the lowest values were noted in T₁ (flooding throughout the growth period). The highest As concentration in rice grain (0.52 mg kg⁻¹) was found in T₁ and the lowest As concentration in grain (0.27 mg kg⁻¹) was found in T₇. Estimation of the human health risk revealed that the non-carcinogenic risks (HQ > 1) and carcinogenic risks (CR > 1.0 × 10⁻⁴) were greatly affected by different water regimes. The rice plant grown under alternate wetting and drying condition (T₇) showed the lowest health risks compared to other water management practices. Thus, alternate wetting and drying conditions are a good water management strategy for increasing rice output while reducing arsenic buildup in rice grain.