A review of soil NO transformation: Associated processes and possible physiological significance on organisms

NO emissions from soils and ecosystems are of outstanding importance for atmospheric chemistry. Here we review the current knowledge on processes involved in the formation and consumption of NO in soils, the importance of NO for the physiological functioning of different organisms, and for inter- and intra-species signaling and competition, e.g. in the rooting zone between microbes and plants. We also show that prokaryotes and eukaryotes are able to produce NO by multiple pathways and that unspecific enzymo-oxidative mechanisms of NO production are likely to occur in soils. Nitric oxide production in soils is not only linked to NO production by nitrifying and denitrifying microorganisms, but also linked to extracellular enzymes from a wide range of microorganisms.Further investigations are needed to clarify molecular mechanisms of NO production and consumption, its controlling factors, and the significance of NO as a regulator for microbial, animal and plant processes. Such process understanding is required to elucidate the importance of soils as sources (and sinks) for atmospheric NO.     

Monitoring wheat phenology and irrigation in Central Morocco: On the use of relationships between evapotranspiration,crops coefficients,leaf area index and remotely-sensed vegetation indices

The monitoring of crop production and irrigation at a regional scale can be based on the use of ecosystem process models and remote sensing data. The former simulate the time courses of the main biophysical variables which affect crop photosynthesis and water consumption at a fine time step (hourly or daily); the latter allows to provide the spatial distribution of these variables over a region of interest at a time span from 10 days to a month. In this context, this study investigates the feasibility of using the normalised difference vegetation index (NDVI) derived from remote sensing data to provide indirect estimates of: (1) the leaf area index (LAI), which is a key-variable of many crop process models; and (2) crop coefficients, which represent the ratio of actual (AET) to reference (ET₀) evapotranspiration.A first analysis is performed based on a dataset collected at field in an irrigated area of the Haouz plain (region of Marrakesh, Central Morocco) during the 2002–2003 agricultural season. The seasonal courses of NDVI, LAI, AET and ET₀ have been compared, then crop coefficients have been calculated using a method that allows roughly to separate soil evaporation from plant transpiration. This allows to compute the crop basal coefficient (K_cb) restricted to the plant transpiration process. Finally, three relationships have been established. The relationships between LAI and NDVI as well as between LAI and K_cb were found both exponential, with associated errors of 30% and 15%, respectively. Because the NDVI saturates at high LAI values (>4), the use of remotely-sensed data results in poor accuracy of LAI estimates for well-developed canopies. However, this inaccuracy was not found critical for transpiration estimates since AET appears limited to ET₀ for well-developed canopies. As a consequence, the relationship between NDVI and K_cb was found linear and of good accuracy (15%).Based on these relationships, maps of LAI and transpiration requirements have been derived from two Landsat7-ETM+ images acquired at the beginning and the middle of the agricultural season. These maps show the space and time variability in crop development and water requirements over a 3 km × 3 km irrigated area that surrounds the fields of study. They may give an indication on how the water should be distributed over the area of interest in order to improve the efficiency of irrigation. The availability, in the near future, of Earth Observation Systems designed to provide both high spatial resolution (10 m) and frequent revisit (day) would make it feasible to set up such approaches for the operational monitoring of crop phenology and irrigation at a regional scale.     

Yield performance of spring wheat improved by regulated deficit irrigation in an arid area

A field experiment was conducted in 2003 and 2004 growing seasons to evaluate the effects of regulated deficit irrigation on yield performance in spring wheat (Triticum aestivum) in an arid area. Three regulated deficit irrigation treatments designed to subject the crops to various degrees of soil water deficit at different stages of crop development and a no-soil-water-deficit control was established. Soil moisture was measured gravimetrically in the increment of 0–20 cm every five to seven days in the given growth periods, while that in 20 increments to 40, 40–60, 60–80, and 80–100 cm depth measured by neutron probe. Compared to the no-soil-water-deficit treatment, grain yield, biomass, harvest index, water use efficiency (WUE), and water supply use efficiency (WsUE) in spring wheat were all greatly improved by 16.6–25.0, 12.4–19.2, 23.5–27.3, 32.7–39.9, and 44.6–58.8% under regulated deficit irrigation, and better yield components such as thousand-grain weight, grain weight per spike, number of grain, length of spike, and fertile spikelet number were also obtained, but irrigation water was substantially decreased by 14.0–22.9%. The patterns of soil moisture were similar in the regulated deficit treatments, and the soil moisture contents were greatly decreased by regulated deficit irrigation during wheat growing seasons. Significant differences were found between the no-soil-water-deficit treatment and the regulated soil water deficit treatments in grain yield, yield components, biomass, harvest index, WUE, and WsUE, but no significant differences occurred within the regulated soil water deficit treatments. Yield performance proved that regulated deficit irrigation treatment subjected to medium soil water deficit both during the middle vegetative stage (jointing) and the late reproductive stages (filling and maturity or filling) while subjected to no-soil-water-deficit both during the late vegetative stage (booting) and the early reproductive stage (heading) (MNNM) had the highest yield increase of 25.0 and 14.0% of significant water-saving, therefore, the optimum controlled soil water deficit levels in this study should range 50–60% of field water capacity (FWC) at the middle vegetative growth period (jointing), and 65–70% of FWC at both of the late vegetative period (booting) and early reproductive period (heading) followed by 50–60% of FWC at the late reproductive periods (the end of filling or filling and maturity) in treatment MNNM, with the corresponding optimum total irrigation water of 338 mm. In addition, the relationships among grain yield, biomass, and harvest index, the relationship between grain yield and WUE, WsUE, and the relationship between harvest index and WUE, WsUE under regulated deficit irrigation were also estimated through linear or non-linear regression models, which indicate that the highest grain yield was associated with the maximum biomass, harvest index, and water supply use efficiency, but not with the highest water use efficiency, which was reached by appropriate controlling soil moisture content and water consumption. The relations also indicate that the harvest index was associated with the maximum biomass and water supply use efficiency, but not with the highest water use efficiency.     

Management of declining groundwater in the Trans Indo-Gangetic Plain (India): Some options

The average productivity of rice–wheat sequence is quite impressive in the Trans Indo-Gangetic Plain (India) but these gains are over-shadowed due to declining groundwater, particularly in the areas, where groundwater quality is either good or marginal. The groundwater decline can be reversed through artificial groundwater recharge and by adopting suitable land and water management practices. Groundwater recharge is found technically feasible through vertical shafts conducting water from the ground surface directly to aquifers, after it has been passed through a sand-gravel filter. The recharge rate through this system is almost equal to a shallow cavity/filter well yield (about 11 l/s) and its cost is estimated at about INR 10/100 m³ (1 US$ = 45 INR). Further study in the Kaithal and Karnal districts of Haryana for stabilizing watertable within 6–7 m, which permits continuous use of shallow tubewell technology, indicated that the rice area could be supported at 60% of cultivable command area (CCA) and wheat between 65 and 80% of CCA with the existing management practices. The cultivation of wheat crop is sustainable in larger area, mainly due to its medium water requirement, salt resistance characteristics and consistent market demand resulting in assured returns. There is a possibility of supporting rice at a higher level, if part of the area (up to 10%) is left fallow and used for rainwater conservation and recharge. The fallow area may be subsequently put under early rabi (winter) crops like mustard, gram and other pulses. The effect of varying irrigation and fallowing would increase 23% equivalent wheat yield by changing land and water management practices. The analysis further indicated that the adoption of proposed irrigation management practices might stabilize watertable at desired level of 6–7 m in 10–15 years in high (3–4 m), 5 years in medium (5–10 m) and 40 years in deep (>10 m) watertable areas.     

Agronomic performance of late-season rice under different tillage,straw, and nitrogen management

In double rice-cropping system in China, zero tillage in late-season rice with straw return from early season rice is an emerging technology for saving inputs, shortening the lag time between rice crops, avoiding straw burning, and conserving natural resources. The objective of this 2-year field study was to determine the effects of tillage and straw return on N uptake, grain yield, and N use efficiency of late-season rice. Treatments were arranged in a split-plot design with four combinations of tillage and straw return as main plots and three N management practices as subplots. Tillage was either conventional soil puddling or zero tillage with newly harvested crop residue from early season rice either removed or placed on the soil surface without incorporation. The N treatments were zero-N control, site-specific N management (SSNM), and farmers’ N-fertilizer practice (FFP). Straw return regardless of tillage or N management did not reduce rice yield. In the second year, straw return significantly increased grain yield in the zero-N control. Chlorophyll meter readings at heading and total N uptake at maturity were higher with straw return in the zero-N control, suggesting that straw provides nutrients to rice in the late growing period. Zero tillage did not reduce N uptake, grain yield, and N use efficiency compared with conventional tillage. Despite large differences in timing and rate of N application between FFP and SSNM, these two N treatments resulted in comparable N uptake and grain yield of late-season rice regardless of tillage and straw return. These results suggest that zero tillage after early rice with straw return could replace conventional tillage for late rice in the double rice-cropping system in China.     

Simulated rain addition modifies diurnal patterns and temperature sensitivities of autotrophic and heterotrophic soil respiration in an arid desert ecosystem

The timing and magnitude of rainfall events in arid and semiarid regions are expected to change dramatically in future decades, which will likely greatly affect regional carbon cycles. To understand how increases in rainfall affect the diurnal patterns and temperature sensitivities (Q₁₀) of soil respiration (R_S) and its key components (i.e. heterotrophic respiration (R_H) and autotrophic respiration (R_A)), we conducted a manipulative field experiment in a desert ecosystem of Northwest China. We simulated five different scenarios of future rain regimes (0%, 25%, 50%, 75% and 100% increase over local annual mean precipitation) each month from May to September in 2009. We measured R_S and R_H every three hours on 6 and 16 days after the rain addition, and estimated R_A by calculating the difference between R_S and R_H. We found that rain addition significantly increased the daily mean R_S and its components on the two measurement days during the growing season. However, the diurnal pattern was different between the two respiration components. Rain addition significantly increased the daily Q₁₀ value of R_H but suppressed that of R_A on Day 6. Rain addition had no influence on daily Q₁₀ value of both respiration components on Day 16 when soil moisture was lower. In addition, we observed significantly higher daily Q₁₀ of R_H than R_A under all five rain addition treatments, indicating that microbial respiration is more temperature sensitive than root respiration in a short-time scale in this desert ecosystem. Thus, partitioning soil respiration into its two components, and analyzing the differential responses of R_H and R_A to future climate changes should be considered for more accurate predictions of soil respiration and regional carbon cycle in these arid and semiarid regions.     

未来气候情景内蒙古蒸散和产水量的变化特征

评估预测区域蒸散变化趋势及其影响因素对干旱半干旱区的可持续发展至关重要。基于4种来自CMIP 5的全球气候模式数据和CLM 4.5模型,研究了在RCP 6.0和RCP 8.5情景下内蒙古地区2020—2099年的蒸散和产水量的时空变化特征及其影响因素。结果表明：在RCP 6.0和RCP 8.5情景下,未来内蒙古蒸散分别以0.37,0.69 mm/a速度增加（p<0.05）,呈西低东高分布。2种情景下产水量均无明显变化趋势（p>0.05）,但是存在明显显著的空间差异。空间上看,到21世纪末,在RCP 6.0情景下,全境产水量大部分地区呈增加趋势,在南部温带半干旱和半湿润区增加超过10 mm/a;但是在RCP 8.5情景下产水量减少区域占全境的46.32%,特别是干旱半干旱区和半湿润区产水量显著减少。蒸散影响因子存在较大区域差异,干旱半干旱区蒸散变化的主要影响因素是降水,半湿润区蒸散变化受降水和温度的共同影响,湿润区蒸散变化由温度主导;且在更高的升温情景下,增温影响进一步增加。同时,植被也是蒸散重要的影响因子,但其影响程度小于气候因子。     

基于遥感和地面试验的水分指数与土壤湿度及生理指标关系

为研究作物生长发育早期受干旱影响的作物水分光谱特征,对冬小麦返青期进行水分控制试验。利用野外光谱辐射仪在河北固城试验区测量冬小麦的光谱并分别计算归一化水分指数（NDWI）和简单比值水分指数（SRWI）,同时测定冬小麦的叶绿素浓度（Chl）、叶面积指数（LAI）、株高（H）和叶片相对含水率（LRWC）等冠层生理指标和土壤湿度（SM）。分析结果表明：冬小麦生理指标与土壤湿度之间有着显著的正相关,最大相关系数为0.657,表明土壤水分状况直接影响作物发育早期的光合和生长状况。NDWI/SRWI与SM相关系数均为 0.545,呈现弱的正相关;相反,水分指数与冬小麦生理指标之间的相关不明显,特别是,NDWI/SRWI与LRWC的相关系数仅为0.175。据此得出在作物低覆盖生长阶段,水分指数更多反映的是土壤水分状况而不是作物水分。     

The effect of plastic mulch on the fate of urea-N in rain-fed maize production in a semiarid environment as assessed by 15N-labeling

A better understanding of the fate of fertilizer nitrogen (N) is critical to design appropriate N management strategies in plastic-mulched croplands. We evaluated the effects of plastic mulch on urea-N recovery by crops and loss from soil in furrow-ridge plots, with and without maize (Zea mays L.) cropping, in a semi-arid rain-fed site in China. We applied the same rate of urea-N (281 kg ha⁻¹) to all treatments during the preparation of the furrow-ridges in 2011 and 2012 but ¹⁵N-labeled the urea in 2011 only. We used transparent film to cover all soil surfaces in the mulched treatments and seeded maize in furrows in treatments with crop. In 2011, plastic mulch increased the total N uptake in the aboveground biomass of maize by 53%, whereas it decreased the in-season labeled-N uptake by 19%, compared to non-mulched treatment. At harvest in 2011, in mulched treatments the total labeled-N remaining in the 0−170 cm soil layer was 25% greater whereas unaccounted labeled-N was 69% less, than in non-mulched treatments, regardless of whether maize was cropped. In 2012 the effect of mulch on total maize N uptake was comparable to that in 2011, but the residual soil labeled-N uptake by maize was 63% higher in mulched compared to non-mulched treatment. At harvest in 2012, plastic mulch increased total labeled-N remaining in the 0−170 cm depth in cropped soils and unaccounted labeled-N in non-cropped soils, compared with no mulch. Our results indicate that plastic mulch profoundly changes the fate of urea-N in maize production in cold and dry croplands.     

水溶性有机质对南京城郊菜地土壤Pb吸附解吸行为的影响

通过批处理试验研究了不同来源的水溶性有机质（DOM）对南京城郊菜地土壤铅（Pb）吸附解吸行为的影响。研究结果表明,DOM抑制了土壤对Pb的吸附,随着DOM浓度的增加,土壤对Pb的吸附量减少,当DOM体积从0增加到21 mL时,土壤对Pb的吸附量分别减少5.34%（鸡粪）、24.12%（牛粪）和0.35%（有机肥）。不同来源的DOM也影响土壤对Pb的吸附程度。当添加低浓度的DOM（添加体积小于6 mL）时,土壤对Pb的吸附量顺序为鸡粪DOM〈牛粪DOM≈有机肥DOM;当添加高浓度的DOM（添加体积大于6 mL）时,土壤对Pb的吸附量顺序为牛粪DOM〈鸡粪DOM〈有机肥DOM。反之亦然,DOM促进了土壤Pb的解吸,解吸量随添加DOM浓度的增大而增加。不同来源的DOM对土壤Pb解吸程度的影响也有所差异。对于低污染土壤,Pb的解吸量顺序为鸡粪DOM〉牛粪DOM〉有机肥DOM;对于高污染土壤,Pb的解吸量顺序为鸡粪DOM〉有机肥DOM〉牛粪DOM。Pb吸附动力学曲线揭示,添加DOM延缓了土壤Pb吸附平衡到达的时间。本研究表明,DOM增加了土壤Pb的环境风险。