Muhammad Shaaban

Nitrous oxide emission from two acidic soils as affected by dolomite application

The effect of dolomite (CaMg(CO3)2) application on nitrous oxide (N2O) emission was examined in a laboratory study with soil from a rice paddy–rapeseed rotation (PR soil, pH 5.25) and from a rice paddy–fallow–flooded rotation soil (PF soil, pH 5.52). The soils were treated with 0, 0.5 (L) and 1.5 (H) g dolomite 100 g–1 soil. Results showed that N2O emissions were higher in control treatments (untreated dolomite) in both soils. Application of dolomite decreased N2O emissions significantly (P ≤ 0.001) as soil pH increased in both soils. The H treatment was more effective than the L treatment for the reduction of N2O emissions. The H treatment decreased the cumulative N2O emissions by up to 73.77% in PR soil and 64.07% in PF soil compared with the control. The application of dolomite also affected concentrations of dissolved organic carbon, microbial biomass carbon, ammonium and nitrate in soils, which related to N2O emission. The results suggest that dolomite not only counteracts soil acidification but also has the potential to mitigate N2O emissions in acidic soils.

Conversion from rice to vegetable production increases N2O emission via increased soil organic matter mineralization

The conversion from rice to vegetable production widely occurs in China. However, the effects of this conversion on N2O emission and the underlying mechanisms are not well understood. In the present study, 12 rice paddies (R) were selected and half of them converted to vegetable fields (V) with the following treatments: rice paddies without N-fertilizer (R-CK), rice paddies with conventional N-fertilizer (R-CN), converted vegetable fields without N-fertilizer (V-CK), and converted vegetable fields with conventional N-fertilizer (V-CN) in a randomized block design with 3 replicates. N2O emissions were measured with static chambers from December 2012 to December 2015. Within each V-CN plot, a root exclusion subplot was established to measure soil heterotrophic respiration (CO2 effluxes), a proxy for soil organic matter mineralization. Conversion of rice paddies to vegetable production dramatically increased N2O emissions. The three-year cumulative N2O emissions were 0.59, 1.90, 55.50 and 160.14kg N ha-1 for R-CK, R-CN, V-CK and V-CN, respectively. The annual N2O emissions from vegetable fields ranged between 5.99 and 113.45kg N ha-1yr-1, with substantially higher emissions in the first year. N2O fluxes from V-CN were significantly and positively related to CO2 fluxes and inorganic N concentrations. The linear relationship between natural logarithms of N2O and CO2 fluxes was stronger and the regression coefficient higher in the first year, showing the dependence of N2O on soil organic matter mineralization. These results suggest that soil organic matter and N mineralization contributes significantly to N2O emission following conversion of rice paddies to vegetable production.

Effect of straw returning in winter fallow in Chinese rice fields on greenhouse gas emissions: evidence from an incubation study

Many studies have been performed to compare different straw-returning methods that could provide environmental benefits. However, few studies have focused on the greenhouse gas emissions from straw returning under winter water-stored fields (flooded conditions) and winter fallow fields (non-flooded conditions), which are the common land use types after the rice harvest in southern China. Thus, in the present microcosm incubation experiment, CO2, CH4 and N2O emissions were compared under flooded and non-flooded soil conditions, following straw incorporation. Straw application stimulated CO2 cumulative emission, and this effect was exacerbated by flooding (1818 and 4271 mg kg–1 under non-flooded and flooded conditions, respectively). Although the application of straw can mitigate N2O cumulative emissions under flooded conditions (10 152 μg kg–1 without and –51 μg kg–1 with straw incorporation, respectively), higher CO2 and CH4 production was detected (4271 and 149.20 mg kg–1 for CO2 and CH4 cumulative emissions, respectively). In contrast, straw application under non-flooded conditions had a relatively low global warming potential value (1836 mg CO2 Eq kg–1). Consequently, winter fallow field is recommended after the integrated application of straw and nitrogen fertiliser because of its low global warming potential. However, different strategies may be required for long-term reduction in global warming potential values.

The efficacy of Beauveria bassiana, jasmonic acid and chlorantraniliprole on larval populations of Helicoverpa armigera in chickpea crop ecosystems.

BACKGROUND A robust integrated pest management (IPM) programme is needed to reduce the use of insecticides in controlling Helicoverpa armigera. Therefore, a 2 year field study was conducted to evaluate the use of alternative control measures (biochemical use) for H. armigera relative to exclusively using chemical insecticides. The entomopathogenic fungus Beauveria bassiana, jasmonic acid and the insecticide chlorantraniliprole were each applied twice during the chickpea growing season. RESULTS All three applied materials (either alone or combined) significantly (P ≤ 0.05) reduced the larval population of H. armigera and pod infestation. Effects increased with time, and the maximum difference was observed 7 days after the second application in each year. The lowest numbers of larvae per plant and pod infestation were in the B. bassiana 3.21 × 106 + chlorantraniliprole treatment in both 2009/2010 and 2010/2011 year. The reduction in the larval population and pod infestation increased chickpea yield and the highest yield in both seasons, and the maximum yield was obtained in the B. bassiana 3.21 × 106 + chlorantraniliprole treatment. The populations of natural enemies were highest in the jasmonic acid treatment. CONCLUSION The results suggest that B. bassiana, jasmonic acid and chlorantraniliprole may be useful components for the H. armigera IPM strategy.

Effects of soluble organic carbon addition on CH4 and CO2 emissions from paddy soils regulated by iron reduction processes

An incubation experiment with the addition of glucose was conducted to evaluate the effects of carbon and iron (Fe(III)) reduction on methane (CH4) and carbon dioxide (CO2) emissions from paddy soils. Soils of a rice–rapeseed (Brassica napus) rotation and rice–fallow/flooded rotation were collected from Qianjiang (QR and QF, respectively) and Xianning (XR and XF). Incubation was conducted under flooding at 25°C ± 1°C with or without (CK) glucose over 40 days. With glucose addition, cumulative CH4-C emissions from QR, QF, XR and XF soils were 5.31, 35.26, 13.92 and 27.58 mg kg–1, respectively, and cumulative CO2-C emissions were 594.33, 620.49, 549.42 and 792.46 mg kg–1. Compared with CK, glucose addition significantly (P < 0.05) increased cumulative CH4 fluxes in QR and QF soils 11.07-fold and 1.39-fold, respectively, and cumulative CO2 fluxes 0.41-fold and 0.44-fold, whereas the effects of glucose addition on CH4 and CO2 fluxes in XR and XF soils were negligible. In addition, the soil Fe(II)/(Fe(II) + Fe(III)) fraction correlated positively with CH4 fluxes during the major emission period (P < 0.05), and the Fe(II) production rate was positively correlated with the CO2 flux during the whole incubation period. Furthermore, Fe(III) reduction strongly competed with CH4 emission, especially in XR and XF soils, which derived from quaternary red clay. The results suggest that Fe(III) reduction plays a key role in mediating the carbon cycle of paddy soils.

Assessing soil nitrous oxide emission as affected by phosphorus and nitrogen addition under two moisture levels

Abstract Agricultural soils are deficient of phosphorus (P) worldwide. Phosphatic fertilizers are therefore applied to agricultural soils to improve the fertility and to increase the crop yield. However, the effect of phosphorus application on soil N 2 O emissions has rarely been studied. Therefore, we conducted a laboratory study to investigate the effects P addition on soil N 2 O emissions from P deficient alluvial soil under two levels of nitrogen (N) fertilizer and soil moisture. Treatments were arranged as follows: P (0 and 20 mg P kg −1 ) was applied to soil under two moisture levels of 60 and 90% water filled pore space (WFPS). Each P and moisture treatment was further treated with two levels of N fertilizer (0 and 200 mg N kg −1 as urea). Soil variables including mineral nitrogen (NH 4 +-N and NO 3 − -N), available P, dissolved organic carbon (DOC), and soil N 2 O emissions were measured throughout the study period of 50 days. Results showed that addition of P increased N 2 O emissions either under 60% WFPS or 90% WFPS conditions. Higher N 2 O emissions were observed under 90% WFPS when compared to 60% WFPS. Application of N fertilizer also enhanced N 2 O emissions and the highest emissions were 141 μg N 2 O kg −1 h −1 in P+N treatment under 90% WFPS. The results of the present study suggest that P application markedly increases soil N 2 O emissions under both low and high soil moisture levels, and either with or without N fertilizer application.

Changes in the soil N potential mineralization and nitrification in a rice paddy after 20 yr application of chemical fertilizers and organic matter

Abstract: The effect of long-term (20 yr) fertilizer application on soil nitrogen (N) transformation in paddy soils was studied at three sites (Xinhua, Ningxiang, and Taojiang) in Hunan province, China. Four fertilization practices were chosen: chemical fertilizers (NPK), chemical fertilizers plus a medium or high amount of pig manure (MM + NPK), chemical fertilizers plus a high amount of pig manure (HM + NPK), and chemical fertilizers plus straw incorporated (Str. + NPK). A treatment with no fertilization was included as a control (CK). Ten week aerobic incubations were conducted to determine N potential mineralization and nitrification. Application of organic plus chemical fertilizer increased soil organic carbon, total nitrogen, and microbial biomass carbon (Cmic) and nitrogen (Nmic), whereas the response of Cmic/Nmic ratio to fertilizer application varied among sites. Across all sites, the HM + NPK treatments had the highest potentially mineralizable N and maximal nitrification rate, and the CK had the lowest. The MM + NPK, Str. + NPK, and NPK treatments had lesser effects on mineralizable N and nitrification. Results indicated that chemical fertilizer along with a high rate of manure application is an effective method to improve available soil N by increasing the N mineralization rate. However, higher N nitrification was also induced by manure application, which may lead to increased N losses, and also should be considered in practical applications.

Carbon budget and greenhouse gas balance during the initial years after rice paddy conversion to vegetable cultivation

Rice paddy conversion to vegetable production is a common agricultural practice driven by economic benefits and shifting diets. However, little is known on the initial effects of this land-use conversion on net ecosystem carbon budget (NECB) and greenhouse gas (GHG) balance. Annual NECB and emissions of CH4 and N2O were measured from a native double rice cropping system (Rice) and a vegetable field recently converted from rice paddy (Veg) under no nitrogen (N) fertilization (Rice-N0 and Veg-N0) and conventional N fertilization (Rice-N+ and Veg-N+) during the initial four years upon conversion in subtropical China. Land-use conversion from rice to vegetable cultivation led to substantial C losses (2.6 to 4.5 Mg C ha-1 yr-1), resulting from strongly reduced C input by 44-52% and increased soil organic matter mineralization by 46-59% relative to Rice. The magnitude of C losses from Veg was highest in the first year upon conversion, and showed a decreasing trend over time. N fertilization shifted rice paddy from a slight C source in Rice-N0 (-1.0 Mg C ha-1 yr-1) to a significant C sink in Rice-N+ (1.1 Mg C ha-1 yr-1) and alleviated the impact of land-use conversion on C loss via increased C input from higher crop productivity. Land-use conversion greatly increased the global warming potential (GWP) from Veg by 116-395% relative to Rice in the first year, primarily due to increased C losses and N2O emission outweighing the decreased CH4 emission. However, the GWP did not show obvious difference between Rice and Veg in the following years. N fertilization and land-use conversion interactively increased GWP in the first year via increased N2O production. Concluding, NECB and GHG emissions in the first year after conversion are crucial and should be considered when evaluating the environmental consequences of land-use conversion.

Reduction in soil N 2 O emissions by pH manipulation and enhanced nosZ gene transcription under different water regimes

Several studies have been carried out to examine nitrous oxide (N2O) emissions from agricultural soils in the past. However, the emissions of N2O particularly during amelioration of acidic soils have been rarely studied. We carried out the present study using a rice-rapeseed rotation soil (pH 5.44) that was amended with dolomite (0, 1 and 2 g kg-1 soil) under 60% water filled pore space (WFPS) and flooding. N2O emissions and several soil properties (pH, NH4+N, NO3--N, and nosZ gene transcripts) were measured throughout the study. The increase in soil pH with dolomite application triggered soil N transformation and transcripts of nosZ gene controlling N2O emissions under both water regimes (60% WFPS and flooding). The 60% WFPS produced higher soil N2O emissions than that of flooding, and dolomite largely reduced N2O emissions at higher pH under both water regimes through enhanced transcription of nosZ gene. The results suggest that ameliorating soil acidity with dolomite can substantially mitigate N2O emissions through promoting nosZ gene transcription.

Efficiency of C3 and C4 Plant Derived-Biochar for Cd Mobility, Nutrient Cycling and Microbial Biomass in Contaminated Soil

Biochar is considered a novel soil amendment to reduce metal mobility, but its influence on soil chemical and biochemical properties is not fully understood. In the present study, biochar derived from rice straw (RSB), rice hull (RHB), and maize stover (MSB) was used to evaluate comparative efficiency on Cd mobility and soil biochemical properties. Ammonium nitrate extractable Cd significantly decreased among all the applied biochar types and application rates. The European Community Bureau of Reference (BCR) technique showed significant decrease in acid-soluble Cd by 24%–32%, 19%–23%, and 22%–27% for RSB, RHB, and MSB, respectively at the 1.5% and 3% rate. However, the concentration of Cd in the residual increased by 38%, 35% and 36% for RSB, RHB and MSB, respectively at a 3% application rate. Soil microbial biomass (C and N) and inorganic nitrogen forms (NH4 and NO3) significantly increased among all biochar applications. Overall, RSB demonstrated positive results as soil amendments for Cd immobilization, increasing soil nutrient availability, and enhancing soil microbial biomass.