Search

Aim: Nitrogen use efficiency (NUE) in subtropical cropping systems is low causing a large quantity of reactive N loss to the environment. However, the mechanisms and pathways of such losses are poorly understood. The objectives of the research were to quantify N volatilization rates and corresponding NUE in a biochar and nitrapyrin-treated cabbage field using N-control as well as a 15N-based approach. Methods: The treatments consisted of: N-control, urea alone, urea with nitrapyrin (UN), urea with biochar (UB), and urea with biochar and nitrapyrin (UNB). In each plot, 15N-labeled urea was applied in 1 m2 micro-plots to repeat the treatments. Results: The UNB had higher (p < 0.001) crop yields than other treatments by 29, 23 and 16% over the urea, UN and UB treatments, respectively, while the UN and UB were also higher than the urea alone. The estimated 15N-based NUE was higher (p < 0.01) in the UNB (40%) than in the urea alone (32%) but similar to the UN (36%) and UB (38%). The N-control based calculation overestimated NUE by 2–13% relative to the 15N-based approach. The UNB treatment reduced NH3 volatilization by 37, 22, and 33% over urea alone, UB and UN, respectively (p < 0.01). Post-harvest soil organic carbon (SOC) and total N were higher (p < 0.001) in the UNB and UB treatments than the other treatments. Conclusion: Our results with a subtropical crop suggest that biochar alone or co-applied with nitrapyrin improves NUE and mitigates NH3 volatilization while increasing SOC and TN contents. [ABSTRACT FROM AUTHOR]

Shallow tube well (STW) water, often contaminated with arsenic (As), is used extensively in Bangladesh for irrigating rice fields in the dry season, leading to potential As accumulation in soils. In the current study the consequences of arsenic from irrigation water and direct surface (0–15 cm) soil application were studied under field conditions with wetland rice culture over 2 years. Twenty PVC cylinders (30-cm length and 30-cm diameter) were installed in field plots to evaluate the mobility and vertical distribution of soil As, As mass balance, and the resulting influences on rice yield and plant-As concentration in Boro (dry season) and transplanted (T.) Aman (wet season) rice over the 2-year growth cycle. Treatments included irrigation-water As concentrations of 0, 1 and 2 mg L−1 ( Boro season only) and soil-As concentrations of 10 and 20 mg kg−1. Following the 2-year cropping sequence the major portion (39.3–47.6%) of the applied arsenic was retained within the rooting zone at 0–15 cm depth, with 14.7–19.5% of the total applied As at the 5–10 cm and 10–15 cm soil depths compared to 1.3–3.6% at the 35–40 cm soil depth. These results indicate the relatively low mobility of applied As and the likely continued detrimental accumulation of As within the rooting zone. Arsenic addition in either irrigation water or as soil-applied As resulted in yield reductions from 21 to 74 % in Boro rice and 8 to 80 % in T. Aman rice, the latter indicating the strong residual effect of As on subsequent crops. The As concentrations in rice grain (0.22 to 0.81 µg g−1), straw (2.64 to 12.52 µg g−1) and husk (1.20 to 2.48 µg g−1) increased with increasing addition of As. These results indicate the detrimental impacts of continued long-term irrigation with As-contaminated water on agricultural sustainability, food security and food quality in Bangladesh. A critical need exists for the development of crop and water management strategies to minimize potential As hazard in wetland rice production. [ABSTRACT FROM AUTHOR]

An experiment involving four soils and three irrigation-water As concentrations was conducted in undisturbed soil columns during 2004–2006, with Boro (winter dry-season, flood-irrigated rice, using As-contaminated water for irrigation), T. Aman (summer monsoon, rain-fed flooded rice), Boro, and T. Aman rice grown in sequence, to examine the fate of added As from irrigation water during flooded rice culture. The As content in the column leachate represented only 1.17–5.08% of the total applied As, indicating the substantial build-up of soil As. Most of the irrigation-applied As remained in the zone of maximum root activity at the top 0–15 cm of soil. Increased As concentrations in soil from the application of As-contaminated water resulted in substantially reduced rice-grain yields and increased As concentrations in rice grain and straw, indicating the potential hazards of continued irrigation with As-contaminated water to sustainable rice production and food security in South Asia. [ABSTRACT FROM AUTHOR]

The effects of arsenate, Fe2+, and phosphate on amount and composition of Fe-oxide plaque at the rice-root surface and on the yield and arsenic accumulation in rice (cv. BRRI dhan33) were studied in a replicated pot-culture experiment. Arsenic in the form of Na2HAsO4 was applied at concentrations of 0, 15 and 30 mg kg−1 in combination with P and/or Fe at 0 and 50 mg kg−1, from KH2PO4 and FeSO4, respectively. Root, grain and straw yields and their As, Fe and P concentrations were determined. The Fe-oxide plaque was extracted from the plant roots using dithionite-citrate-bicarbonate (DCB) and NH4-oxalate extractions. The addition of Fe2+ reduced the toxic effect of As in flooded-rice culture and resulted in reduced grain-As accumulation and increased grain yields. The effect of applied phosphate was the opposite, in that it resulted in higher As concentrations in both grain and straw and lower grain yields. The effects of both Fe and P can be explained based on their impacts on adsorption of As onto soil and rice-plaque Fe-oxides and the subsequent As solubility and availability for uptake by rice. These reactions have important implications to rice-crop management and the natural variability in soils and irrigation-water characteristics that might impact As uptake by rice. [ABSTRACT FROM AUTHOR]

A study was made over 3 years to find out an optimum rate of Zn application for the maize–mungbean–rice cropping system in a calcareous soil of Bangladesh. Zinc application was made at 0, 2 and 4 kg ha−1 for maize (cv. Pacific 984, Thai hybrid) and at 0, 1 and 2 kg ha−1 for rice (cv. BRRI dhan33), with no Zn application for mungbean (cv. BARI mung5). Effect of Zn was evaluated in terms of yield and mineral nutrients contents (N, P, S and Zn). All the three crops responded significantly to Zn application. The optimum rate of Zn for the maize–mungbean–rice cropping system was found to be 4–0–2 kg ha−1 for the first year and 2–0–2 kg ha−1 for subsequent years particularly when mungbean residue was removed, and such rates for mungbean residue incorporation being 4–0–1 and 2–0–1 kg ha−1, respectively. For all crops, the Zn and N concentrations of grain were significantly increased with Zn application. For the case of grain-S, the concentration was significantly increased for maize and mungbean, but it remained unchanged for rice. The grain-P concentration on the other hand tended to decrease with Zn application. For maize, the grain-Zn concentration increased to 27.0 μg g−1 due to 2 kg Zn ha−1 treatment from 16.5 μg g−1 for Zn control and at higher Zn rate (4 kg Zn ha−1) the increment was very minimum. Another field experiment was performed over 3 years on the same soil to screen out maize varieties for Zn efficiency. Of the eight varieties tested, the BARI maize 6 and BARI hybrid maize 3 were found Zn in-responsive (Zn efficient) and the others Zn responsive (Zn-inefficient). [ABSTRACT FROM AUTHOR]