Soil respiratory quotient determined via barometric process separation combined with nitrogen-15 labeling

The barometric process separation (BaPS) and ¹⁵N dilution techniques were used to determine gross nitrification rates on the same soil cores from an old grassland soil. The BaPS-technique separates the O₂ consumption into that from nitrification and that from soil organic matter (SOM) respiration. The most sensitive parameter for the calculations via the BaPS technique is the respiratory quotient (RQ = ∆CO₂/∆O₂) for SOM turnover (RQSOM). Combining both methods (BaPS–¹⁵N ) allowed the determination of the RQSOM. The RQ value determined in such a way is adjusted for the influence of nitrification and denitrification, which are both characterized by totally different RQ values. The results for the grassland soil showed that 6 to 10% of O₂ was consumed by nitrification when incubated at 20°C and 0.49 g H₂O g⁻¹ soil. A set of BaPS measurements with the same soil at various temperature and moisture contents showed that up to 49% of the total O₂ consumption was due to nitrification. The calculated RQSOM values via the BaPS–¹⁵N technique presented here are more closely associated with the overall SOM turnover than the usual net RQ reported in the literature. Furthermore, the RQSOM value provides an overall indication of the decomposability and chemical characteristics of the respired organic material. Hence, it has the potential to serve as a single state index for SOM quality and therefore be a useful index for SOM turnover models based on substrate quality

A hydraulic analysis of shock wave generation mechanism on flat spillway chutes through physical modeling

Shock waves are generated downstream of spillways during flood operations, which have adverse effects on spillway operations. This paper presents the physical model study of shock waves at the Mohmand Dam Spillway project, Pakistan. In this study, hydraulic analysis of shock waves was carried out to investigate its generation mechanism. Different experiments were performed to analyze the rooster tail on a flat spillway chute and to examine the factors affecting the characteristics of the rooster tail. The study results show that shock wave height is influenced by spillway chute slope, pier shape, and flow depth. Moreover, the height of the shock wave can be minimized by installing a semi-elliptical pier on the tail part of the main pier. Further modifications in the geometry of the extended tail part of the pier are recommended for the elimination of the shock wave. Based on observed data collected from the model study, an empirical equation was developed to estimate the shock wave height generated on the flat slope spillway chutes (5◦ to 10◦ )

Effect of soil-applied calcium carbide and plant derivatives on nitrification inhibition and plant growth promotion

The aim of this study was to evaluate the relative performance of three nitrification inhibitors (NIs) viz. calcium carbide (CaC2), and plant derivatives of Pongamia glabra Vent. (karanj) and Melia azedarach (dharek) in regulating N transformations, inhibiting nitrification and improving N recovery in soil-plant systems. In the first experiment under laboratory incubation, soil was amended with N fertilizer diammonium phosphate [(NH4)2sub>HPO4] at a rate of 200 mg N kg-1, N + CaC2, N + karanjin, and N + M. azedarach and incubated at 22 °C for 56 days period. Changes in total mineral N (TMN), NH4 +-N and NO3--N were examined during the study. A second experiment was conducted in a glasshouse using pots to evaluate the response of wheat to these amendments. Results indicated that more than 92 % of the NH4+ initially present had disappeared from the mineral N pool by the end of incubation. Application of NIs i.e., CaC2, karanjin, and M. azedarach resulted in a significant reduction in the extent of NH4+ disappearance by 49, 32, and 13 %, respectively. Accumulation of NO3--N was much higher in N amended soil 57 % compared to 11 % in N + CaC2, 13 % in N + karanjin, and 18 % in N + M. azedarach. Application of NIs significantly increased growth, yield, and N uptake of wheat. The apparent N recovery in N-treated plants was 20 % that was significantly increased to 38, 34, and 37 % with N + CaC2, N + karanjin, and N + M. azedarach, respectively. Among the three NIs tested, CaC2 and karanjin proved highly effective in inhibiting nitrification and retaining NH4+-N in the mineral pool for a longer period

Nitrogen mineralization of a loam soil supplemented with organic-inorganic amendments under laboratory incubation

The quantification of nitrogen (N) supplying capacity of organic amendments applied to a soil is of immense importance to examine synchronization, N release capacity, and fertilizer values of these added materials. The aim of the present study was to determine the potential mineralization of separate and combined use of poultry manure (PM), wheat (Triticum aestivum L.) straw residues (WSR), and urea N (UN) applied to a loam soil and incubated periodically over 140 days period. Treatments included PM100, WSR100, PM50 + WSR50, UN100, UN50 + PM50, UN50 + WSR50, UN50 + PM25 + WSR25, and a control (unfertilized). Added amendments were applied on an N-equivalent basis at the rate of 200 mg N kg−1. Nitrogen supplying capacity of added materials was determined by measuring changes in total mineral N (ammonium-nitrogen and nitrate-nitrogen [NH4+–N + NO3––N]) and accumulation of NO3––N over different incubation periods. Changes in soil organic matter content and total N concentration were also monitored during the study. Results indicated that added amendments released substantial N into the mineral N pool (net cumulative N mineralized) [NCNM] ranged between 39 and 147 mg N kg−1, lowest in the WSR and highest in the UN50+PM50. Significant differences were observed among the amendments and the net inorganic N derived from a separate and combined use of PM was greater than the other treatments. Total inorganic N derived from PM increased from 2.3 mg kg−1 at d 1, to a maximum of 102 to 105 mg kg−1 at 63, 84 and 105 d after PM application. The values were further increase from 31.5 mg kg−1 at d 0 to a maximum of 165 mg kg−1 at d 49 in UN50 + PM50 treatment. The net cumulative N nitrified (NCNN) varied between 16 and 126 mg kg−1, highest in UN50 + PM50 treatment. Soil amended with WSR100 showed negative values both for mineralization and nitrification until day 84, displaying net immobilization. On average, percentage conversion of added N into available N by different amendments varied between 21% to 80%, while conversion of applied N into NO3––N ranged between 9% to 65%, and the treatmen

Ameliorating Effects of Biochar Derived from Poultry Manure and White Clover Residues on Soil Nutrient Status and Plant growth Promotion--Greenhouse Experiments.

Biochar application to agricultural soils is rapidly emerging as a new management strategy for its potential role in carbon sequestration, soil quality improvements, and plant growth promotion. The aim of our study was to investigate the effects of biochars derived from white clover residues and poultry manure on soil quality characteristics, growth and N accumulation in maize (Zea mays L.) and wheat (Triticum aestivum L.) grown in a loam soil under greenhouse conditions. Treatments comprised of: untreated control; mineral N fertilizer (urea N, UN) at the rate of 200, and 100 mg N kg(-1), white clover residues biochar (WCRB), poultry manure biochar (PMB) at 30 Mg ha(-1), and the possible combinations of WCRB+PMB (50:50), UN+WCRB (50:50), UN+PMB (50:50), and UN+WCRB+PMB (50:25:25). The treatments were arranged in a completely randomized design with three replications. Results indicated a significant increase in the growth and biomass production of maize and wheat supplemented with biochars alone or mixed with N fertilizer. Biochars treatments showed varying impact on plant growth depended upon the type of the biochar, and in general plant growth under PMB was significantly higher than that recorded under WCRB. The growth characteristics in the combined treatments (half biochar+half N) were either higher or equivalent to that recorded under full fertilizer N treatment (N200). The biochar treatments WCRB, PMB, and WCRB+PMB (50:50) increased maize shoot N by 18, 26 and 21%, respectively compared to the control while wheat shoot N did not show positive response. The N-uptake by maize treated with WCRB, PMB, and WCRB+PMB (50:50) was 54, 116, and 90 mg g(-1) compared to the 33 mg g(-1) in the control while the N-uptake by wheat was 41, 60, and 53 mg g(-1) compared to 24 mg g(-1) in the control. The mixed treatments (half biochar+half N) increased N-uptake by 2.3 folds in maize and 1.7 to 2.5 folds in wheat compared to the N100 showing increasing effect of biochar on N use efficiency of applied N. Post-harvest soil analysis indicated a significant increase in pH, organic matter, organic C, total N, C:N, and porosity (% pore space) by the added biochars while bulk density (BD) was significantly decreased. The organic matter content in the soil amended with biochars ranged between 19.5 and 23.2 g kg(-1) compared to 11.7 and 10.2 g kg(-1) in the control and N fertilizer treatments while the BD of biochars amended soils (WCRB, PMB, and WCRB+PMB) was 1.07, 1.17, and 1.11 g cm(-3) compared to 1.28 g cm(-1) in the control. In summary, the results of present study highlight the agronomic benefits of biochars in improving the quality of the soil, and promoting growth, yield and N accumulation of both maize and wheat with a consequent benefit to agriculture

Maize biomass production in response to the application of biochars with and without N fertilizer under greenhouse conditions.

<p>Treatments included i.e. T₁ = control, T₂ = urea N (UN) at 200 mg kg^-1, T₃ = urea N (UN) at 100 mg kg^-1, T₄ = white clover residue biochar (WCRB) at 30 t ha^-1, T₅ = poultry manure biochar (PMB) at 30 t ha^-1, T₆ = WCRB+PMB (50:50 w/w), T₇ = UN+WCRB (50:50 w/w), T₈ = UN+PMB (50:50 w/w), and T₉ = UN+WCRB+PMB (50:25:25 w/w). The vertical lines on each bar represent the least significant difference (LSD at <i>P</i> ≤ 0.05) among different treatments for each trait while the letters on each bar highlight the statistical differences among the treatments for the traits studied.</p

Maize and wheat N-uptake (average over stages of development) in response to the application of biochars with and without N fertilizer under greenhouse conditions.

<p>Treatments included i.e. T₁ = control, T₂ = urea N (UN) at 200 mg kg^-1, T₃ = urea N (UN) at 100 mg kg^-1, T₄ = white clover residue biochar (WCRB) at 30 t ha^-1, T₅ = poultry manure biochar (PMB) at 30 t ha^-1, T₆ = WCRB+PMB (50:50 w/w), T₇ = UN+WCRB (50:50 w/w), T₈ = UN+PMB (50:50 w/w), and T₉ = UN+WCRB+PMB (50:25:25 w/w). The vertical lines on each bar represent the least significant difference (LSD at <i>P</i> ≤ 0.05) among different treatments for each trait while the letters on each bar highlight the statistical differences among the treatments for the traits studied.</p