Characteristics of radiative and non-radiative energy fluxes over monsoon trough zone

In order to describe behaviour of radiative and non-radiative erergy fluxes in the surface layer, computation of net radiation, sensible, latent and heat soil flux has been done using hourly global radiation, slow response data of MONTBLEX-90 and surface observation of Varanasi and Jodhpur during rainy and non-rainy days in July 1990. Daily and hourly ground temperature is calculated solving one dimensional heat conduction equation and soil heat flux is computed using force restored method .Outgoing Longwave Radiation (OLR) is calculated by Stefan-Boltzrnann law of radiation and the largest diurnal variability was found over dry convective zone. Results show that OLR from the ground lies in the range 473.0-537.6 Wm-2 at Jodhpur and 497.4 -548.4 Wm-2 at Varanasi during generally cloudy day. The dip in OLR is increascd by 10% with increase of relative humidity and cloudiness. Daily mean of the largest downward soil heat flux are found as 206.4 and 269.4 Wm-2 at Varanasi and Jodhpur respectively during cloudy day. About 40-50% of net radiation is imparted to soil heat flux at Varanasi and Jodhpur. Sum of the hourly non- radiative energy fluxes has not been balanced by net radiation while daily cumulative value of the fluxes balances the net radiation during non-rainy day.

Laboratory and field measurements of HONO emissions from agricultural soils in Guangdong of China

<p>Laboratory studies indicated that soil could produce considerable nitrous acid (HONO) emissions, which is the main primary source of hydroxyl radical (OH) in the troposphere. However, very few field observations of HONO emission from soil were reported. In order to relate laboratory results and field measurements, we measured HONO emissions from 7 representative agricultural soils (rice, vegetables, orchards, peanuts, potatoes, sugarcane and maize) in Guangdong under controlled laboratory conditions, and took flux measurements on 2 of them (rice and vegetables) by dynamic chambers in the field. Generally, release rates of HONO from the seven soils increased with temperature and varied with soil moisture, and the optimum release rates can be reached under specific values of water-filled pore space (WFPS), which is considered to be beneficial to nitrification. The seven soils' optimum release rates ranged from 1.24 to 43.19 ng kg<sup>-1</sup> s<sup>-1</sup>, and the Q<sub>10</sub> (It is defined as the multiple of the increase of soil gas emission rate when the temperature increases by 10℃) ranged from 1.03 to 2.25. Formulas were deduced from the lab results to express HONO emissions for every soil. Flux measurements on two soils varied around -1 to 4 ng N m<sup>-2</sup> s<sup>-1</sup>, and both showed similar diurnal variations with peaks around noontime and very low even negative values during nighttime. There were good correlations between HONO fluxes and soil temperature (R<sup>2</sup>=0.5). Furthermore, irrigation enhanced the HONO emission substantially. However, a large discrepancy existed between soil HONO emissions measured in lab and low HONO fluxes in field. More investigations are needed to explain the paradox.</p>

Measuring frequently during peak soil N₂O emissions is more important than choosing the time of day to sample

Manual gas sampling from static soil chambers is commonly used to measure the flux of nitrous oxide (N2O) from soil. Because manual sampling is labour intensive, sampling frequencies are often insufficient to fully capture daily variability of N2O soil flux, which compromises the accuracy of estimates of daily and cumulative emissions. Knowledge of the diurnal fluctuation of N2O flux has been used to choose a flux sampling time that maximizes the accuracy of N2O flux estimates and thereby reduces the required frequency of flux measurements, but results of previous studies have been inconsistent. We analysed N2O soils emissions measured quasi-continuously over three years from a highly fertilized (> 200 kg N ha−1) maize system grown in southern Wisconsin, USA. This is the first study of N2O flux temporal variability that includes multiple difficult-to-measure peak emission events (hot moments) and estimates the relative contribution of hot moments to cumulative emissions. Analysis of diurnal fluctuation in N2O flux was performed using all measured data (≈ 22 000 fluxes) as well as using subsets of the data grouped by flux magnitude. The relationship between the observed hourly average flux and the mean daily flux was assessed using linear regression. Results show that diurnal variation in N2O soil flux was closely associated with normalized flux size. During low emission periods, N2O soil fluxes exhibited a diurnal pattern such that N2O flux measured at particular times of day, Preferred Measuring Times (PMTs), were not significantly different from the mean daily flux. During high emissions periods N2O flux did not exhibit a diurnal pattern and there was no PMT. High emissions periods included difficult-to-measure hot moments that did not exhibit a PMT and contributed up to 50 % of the cumulative emissions. We conclude that in order to accurately measure soil N2O flux in this type of system, it is necessary to sample frequently, particularly during peak flux events, and that constraining sampling to particular times of day provides little benefit.