Crop row spacing and its influence on the partitioning of evapotranspiration by winter-grown wheat in Northern Syria

A study was conducted during the 1996–97 crop growth season at ICARDA in northern Syria, to investigate the influence of wheat canopy architecture on the partitioning of moisture between soil evaporation and crop transpiration, on a soil with high hydraulic conductivity. The study was conducted on the long-term two course wheat-lentil rotation trial, established on a swelling clay soil (Calcixerollic xerochrept). The wheat canopy architecture was manipulated by sowing the crop at either of two row-spacings, 0.17 or 0.30 m, both at a constant sowing rate equivalent to 120 kg ha^–1. In this study, evapotranspiration from the crop was inferred from changes in soil moisture content over time, evaporation and rainfall interception were measured daily using microlysimetry, drainage was estimated as being the difference between potential daily evapotranspiration, and the evapotranspiration estimated from the soil water deficit. Between sowing and day 80 (tillering stage), evapotranspiration was calculated to consist mainly of soil evaporation. However, after day 80, transpiration became an increasingly dominant component of evapotranspiration. For both row-spacings, cumulative evapotranspiration over the season was approximately 373 mm. In the narrow-row crop, transpiration and soil evaporation were approximately 185 mm and 183 mm of water respectively. Conversely for the wide row-spaced crop, 172 mm of water was transpired while about 205 mm of water evaporated from the soil surface. While green leaf area index did not differ between row-spacings, the architecture of the crops as a result of sowing affected solar radiation penetration such that more incident radiation was intercepted at the soil surface of the wide row-spaced crop. This is likely to have made some contribution to the elevated levels of evaporation from the soil beneath the canopy of the wide-sown crop.     

Temporal and spatial root development of cauliflower (Brassica oleracea L. var. botrytis L.)

Row crops are often inefficient in utilizing soil resources. One reason for this appears to be inefficient rooting of the available soil volume. Five experiments were performed to study the temporal and spatial root development of cauliflower (cv. Plana). The crop was grown with 60 cm between rows, and root development was followed in minirhizotrons placed under the crop rows, 15 cm, and 30 cm from the crop rows. Soil was sampled and analyzed for nitrate content at the final harvest and once during growth. In two of the experiments N fertilizer rate was varied and in two of the other experiments two cultivars were compared (cv. Plana and Siria).The rooting depth of cauliflower was found to be linearly related to temperature sum, with a growth rate of 1.02 mm day^-1 °C^-1. Depending on duration of growth this leads to rooting depths at harvest of 85–115 cm. Soil analysis showed that the cauliflower was able to utilize soil nitrogen down to at least 100 cm.With Plana differences in root growth between row and interrow soil were only observed during early growth, but with Siria this difference was maintained until harvest. However, at harvest both cultivars had depleted row and interrow soil nitrate equally efficient. Nitrogen fertilizer did not affect overall root development significantly.The branching frequency of actively branching roots was increased in all soil layers from about 6 to 10 branches cm^-1 by increasing N fertilizer additions from 130 to 290 kg N ha^-1. Increasing N supply increased the number of actively branching roots in the topsoil and reduced it in the subsoil.The average growth rate of the roots was always highest in the newly rooted soil layers, but fell during time. At 74 days after planting very few roots were growing in the upper 60 cm of the soil whereas 70% of the root tips observed in the 80–100 cm soil layer were actively growing. Within each soil layer there was a large variation in growth rate of individual root tips.     

半干旱黄土丘陵区撂荒坡地土壤水分循环特征

为深入了解半干旱黄土丘陵区土壤水分循环特征和为开展荒地造林工作提供背景数据,在宁南上黄生态试验站,选取典型多年撂荒坡地,进行土壤水分的长期定位观测,分析其土壤水分补给、消耗特征与时空变异性。结果表明:研究区降雨入渗量和入渗深度随降雨量增加而增加,入渗补给系数约为0.44,雨水资源化率有待提高。定义全年一半以上的次降水事件中能被有效补给的土层深度为降水普遍入渗深度,则研究区降水普遍入渗深度为0—40 cm,观测期内最大入渗深度不超过300 cm。同时,土壤水分的蒸散发量在丰水年平水年干旱年,主要蒸散发作用层位于0—200 cm土层范围内,最大蒸散发深度达到300 cm以下。该区土壤储水量的季节变化为"V"型,剖面土壤平均含水量的垂直变异则呈现反"S"型。土壤水分的变异系数随土层深度的增加表现出幂函数递减趋势,结合有序聚类法的分层结果,可采用0.20和0.05两个CV值将撂荒地土壤剖面划分为水分活跃层(0—40 cm)、次活跃层(40—200 cm)和相对稳定层(200 cm以下)3个层次。     

Movement of nitrate,chloride, and potassium in a sandy loam soll

Summary This study was conducted to measure the movement of nitrogen, chloride, and potassium in a sandy loam soil under field conditions and with controlled sprinkle irrigation. After 62.5 mm of water was applied, soil nitrate measurements indicated 67 per cent of the applied N fertilizer was lost from the upper 105 cm of the soil profile. Following a cumulative irrigation of 112.5 mm of water, 82 per cent of the applied N was lost. Since the chloride movement and redistribution was almost identical to the nitrate movement pattern, it would seem plausible that most of the nitrates were lost from the upper part of the soil by leaching. The potassium movement involved the redistribution of exchangeable K from the 0–8 cm soil zone into the 8–15 cm zone and with some buildup of K occurring in the 15–30 cm soil layer. re]19741126 rv]19751111     

Analysis of soil moisture variations in an irrigated orchard root zone

Soil moisture and suction head in an irrigated orchard were continuously monitored by time domain reflectometry (TDR) probes and gypsum blocks, respectively, during and between successive irrigation events. On each side of the trees in the plot, two 30-cm long probes were installed vertically 10 cm below the soil surface (denoted as shallow) and another two probes were installed vertically 40 cm below the soil surface (denoted as deep). The variation in moisture content measured by the TDR probes between successive irrigation events was qualitatively divided into four stages: the first was during water application; the second initiated when irrigation stopped and the moisture content in the layer sharply decreased, mainly due to free drainage. The succeeding moderate soil-moisture decrease, caused by the simultaneous diminishing free drainage and root uptake, was the third stage. During the fourth stage, moisture depletion from the layer was solely by root uptake. The slopes of moisture content variation with time throughout this stage enabled the monitoring of water availability to the plant. The range of moisture content variations and moisture depletion rates between subsequent irrigation events was higher in the shallow (10–40 cm) than in the deeper (40–70 cm) layer. Irrigation nonuniformity and spatial variability of soil hydraulic properties contributed to the unevenness of the moisture distribution in the soil profile. However, as soon as moisture content within a layer reached field capacity, namely the free drainage had stopped, irrigation uniformity had a negligible effect on water flux to the plant roots. The measured data indicate that soil moisture is fully available to the plant as long as the momentary moisture flux from the soil bulk to the soil–root interface can replenish the moisture being depleted to supply, under non-stressed conditions, the atmospheric water demand. This flux is dominated by the local momentary value of the soil's bulk hydraulic conductivity, K _r, and it stays constant for a certain range of K _r values, controlled by the increasing root suction. A decrease in water availability to the plant appears for longer irrigation intervals as a break in the constant soil-moisture depletion rate during stage 4. This break is better correlated to a threshold K _r value than to threshold values of moisture content or suction. Therefore, it is suggested that moisture content or suction used to measure water availability or to control irrigation first be alibrated by K _r() or K _r() curves, respectively.     

华北平原冬小麦农田蒸散量

以华北平原冬小麦农田为研究对象,采用涡度相关技术和热红外遥感技术,研究了不同环境条件下土壤含水量与农田蒸散量及作物冠层温度的关系.结果表明,冬小麦在农田郁闭(LAI≥3)、晴天和土壤相对含水量低于田间持水量65%的情况下,蒸发比值日变化正午前后出现相对较低且平稳的变化趋势.在晴天情况下,农田潜热通量与作物冠层温度日变化和季节变化均呈极显著的非线性相关关系,而冠气温差、农田相对蒸散量则与0～100 cm土层的土壤相对含水量密切相关.以13:30～14:00的平均冠层温度值T_c、日最高气温T_{a max}和日净辐射总量Rn_d为统计数据,确立了冬小麦农田日蒸散量ET_d （mm）估算简化模式参数.     

Root distribution and water uptake patterns of corn under surface and subsurface drip irrigation

Information on root distribution and uptake patterns is useful to better understand crop responses to irrigation and fertigation, especially with the limited wetted soil volumes which develop under drip irrigation. Plant water uptake patterns play an important role in the success of drip irrigation system design and management. Here the root systems of corn were characterized by their length density (RLD) and root water uptake (RWU). Comparisons were made between the spatial patterns of corn RWU and RLD under surface and subsurface drip irrigation in a silt loam soil, considering a drip line on a crop row and between crop rows. Water uptake distribution was measured with an array of TDR probes at high spatial and temporal resolution. Root length density was measured by sampling soil cores on a grid centered on crop row. Roots were separated and an estimation of root geometrical attributes was made using two different image analysis programs. Comparisons of these programs yielded nearly identical estimates of RLD. The spatial patterns of RWU and RLD distributions, respectively normalized to the total uptake and root length, were generally similar only for drip line on a crop row, but with some local variations between the two measures. Both RLD and RWU were adequately fitted with parametric models based on semi-lognormal and normal Gaussian bivariate density functions (Coelho and Or, 1996; Soil Sci. Soc. Am. J. 60, 1039–1049).     

内蒙古典型草原小叶锦鸡儿灌丛化对水分再分配和利用的影响

灌丛化是全球草原地区存在的主要环境问题。通过对内蒙古典型草原区小叶锦鸡儿灌丛和草地斑块冠层降雨再分配、地表径流、土壤含水量的对比观测,研究了小叶锦鸡儿灌丛化对该区水分再分配和利用的影响。结果表明,灌丛和草地斑块的冠层截留量分别占降雨量的20.86%和7.88%,灌丛和草地斑块的平均地表径流系数分别为5.95%和17.19%。土壤含水量观测结果显示,0—60 cm土层中,降雨事件过程中,灌丛斑块较草地斑块能捕获更多水分,灌丛斑块植被冠层下方土壤含水量高于草地斑块;而在雨后无有效降水补充土壤水分的前提下,0—60 cm土层中,灌丛斑块土壤水分蒸散发量高于草地斑块,其中0—10cm土层中灌丛斑块土壤水分蒸散发速率低于草地斑块,10—60 cm土层中灌丛斑块土壤水分蒸散发速率高于草地斑块。研究认为,在水分为关键性限制因子的干旱半干旱区,小叶锦鸡儿灌丛化过程增加草原生态系统中水分分布的空间异质性,灌丛斑块能捕获、利用更多水分以维持更多的生物量。     

Alley cropping with Senna siamea in South-western Nigeria: I. Recovery of 15N labeled urea by the alley cropping system

Improved cropping systems with in-situ production of organic matter require the input of additional inorganic N to maintain crop production in a sustainable way. For proper management of this fertilizer-N, it is necessary to quantify how the applied fertilizer N is used by the various components of the system and by the system as a whole. The fate of a single application of ¹⁵N labeled urea-N through the different components (crop, hedgerow, surface litter, soil profile up to 150 cm) of a Senna siamea alley cropping system, intercropped with maize in the first and cowpea in the second season, was followed for a period of 1.5 years (1994–1995), equivalent to 2 maize and 1 cowpea crop. Special attention was given to the role of the particulate organic matter (POM) in the cycling of urea-N through the soil organic matter (SOM). The maize crop recovered 26.5 and 1.7% of the applied urea-N at harvest in 1994 and 1995, respectively. The cowpea pods recovered only 0.7% of the applied urea-N at harvest. The highest proportion of applied urea-N recovered by the hedgerow occurred at 38 days after 1994 maize planting (DAP) (3.8%), while at later dates, recoveries of applied urea-N were always below 1%. This indicates that the Senna hedge is not a strong competitor for the applied urea-N during crop growth, i.e. while the Senna canopy is pruned at regular intervals. At 21 DAP, 12.7% of the applied urea-N was recovered in the surface litter and this value dropped significantly to 1.6% at 107 DAP and remained below 1% up to 480 DAP. The top 10 cm of soil contained 21% of the applied urea-N at 21 DAP and this value dropped to 9% at 480 DAP. Significantly more urea-N was recovered in the top 10 cm of soil than in the deeper soil layers at all sampling times. At 21 DAP, 11% of the applied urea-N was recovered in the 120–150 cm layer. This fast movement of urea-derived N to deep soil layers must have happened by preferential flow in macropores as the rainfall between urea application and the first sampling (74.2 mm) was not high enough to explain downward movement of N with the mobile water. Significant linear relationships between the proportion of urea-N in the different soil layers (excluding 0–10 cm) and the anion exchange capacity (AEC) and silt+clay content of the respective layers were found at 67, 107, 347 and 480 DAP. The total N content of the POM fraction increased significantly between 0 and 101 DAP from 127 to 171 mg N kg^–1 and decreased to 92 mg N kg^–1 at 480 DAP. The highest recovery of applied urea-N in the POM pool was measured at 101 DAP (3.6%) and this value decreased to 1.8% at 480 DAP. The total recovery of applied urea-N was 81% at 21 DAP, and decreased to values varying between 53 and 60% up from 38 to 347 DAP. At 480 DAP, the recovery decreased further to 47%. The fast movement of a substantial amount of urea-N may be responsible for this incomplete recovery, already at 21 DAP. Although the soil N status in the fertilized alley cropping system appears to be favourable for plant growth, this may be short-lived in the absence of further urea additions, as the soil-derived maize uptake in 1995 was already significantly lower than in 1994, and as the labile POM pool decreased significantly between the maize harvest in 1994 and 1995.     

Influence of tillage on soil macropore size, shape of top layer and crop development in a sub-humid environment

Topsoil macropores of two plots under no-tillage and conventional tillage were analyzed. A leguminous-cereal rotation was applied for six cycles under dry-land farming system (crop residues were removed). The clay-loam soil shows some vertic characteristics. The main goal is to identify the relationship between the top soil macro and meso-pore distribution for the two tillage systems (at the end of sixth cycle of cultivation) with the annual crop production (rainfall in normal growing period and crop production values are included). Unaltered topsoil samples were taken from 0 to 60 mm (row and interrow positions) and from the immediate depth (60 to 110 mm) in both plots (conventional and no-tillage). The morphometric analyses of 66 polished slices were carried out with the aim to identify differences in soil macro and meso-pore organisation. Soil macropores were classified by size (area) and elongation ratio and by form factor and equivalent pore diameter. No appreciable differences were observed. Soil macro and meso-pore distributions of samples were also compared. The main difference observed between topsoil’s treatments was a different macropore size distribution between topsoil positions. The presence of larger macropores was higher in conventional tillage compared to no-tillage. Samples taken from row and deeper positions of conventional tillage show a somewhat higher amount of macropores in the range between 2 to 2.3 mm equivalent pore diameter. Soil macropores contribute to increase soil aeration and soil drying when topsoil is too wet in critical periods of crop development. Conventional tillage (crop residues removed), provides to the topsoil of a larger lateral and vertical variability of macropore distribution than no-tillage topsoil.     

Transformation of15N-labelled urea in rice-wheat cropping system

Summary In a udic chromusterts the transformation of an initial application of¹⁵N-urea @ 80 kg N ha^–1 to rice (Oryza sativa L.) in rice-wheat (R-W) and to wheat (Triticum aestivum L.) in wheat-rice (W-R) rotations was followed in 6 successive crops in each rotation. All rice crops were grown in irrigated wetland and wheat in irrigated upland conditions.The first wheat crop in W-R rotation utilized 22 kg fertilizer N ha^–1 as compared to 19 kg by the corresponding rice crop in R-W rotation. But the latter absorbed more soil N than the former. About 69% of the total N uptake in rice was derived from mineralization of soil organic N as compared to 61% in wheat.The succeeding wheat crop in R-W rotation utilized 6.7% of the residual fertilizer N in the soil but the corresponding rice crop in W-R rotation only 2.2%. The higher utilization appeared to be related to a greater incorporation of labelled fertilizer N in mineral and hexosamine fractions of the soil N. After the second crop in each rotation, the average residual fertilizer N utilization in the next 4 crops ranged between 3 and 4%.The total recovery of¹⁵N-urea in all crops amounted to 21.7 and 24.3 kg N ha^–1 in R-W and W-R rotation, respectively. At the end of the experiment, about 9 to 10 kg ha^–1 of the applied labelled N was found in soil upto 60 cm depth. Most of the labelled soil N (69–76%) was located in the upper 0–20 cm soil layer indicating little movement to lower depths despite intensive cropping for 4 years.     

Effect of crop residues on root growth and phosphorus acquisition of pearl millet in an acid sandy soil in Niger

The effect of long-term (1983–1988) applications of crop residues (millet straw, 2–4 t ha^-1 yr^–1) and/or mineral fertilizer (30 kg N, 13 kg P and 25 kg K ha^-1 yr^-1) on uptake of phosphorus (P) and other nutrients, root growth and mycorrhizal colonization of pearl millet (Pennisetum glaucum L.) was examined for two seasons (1987 and 1988) on an acid sandy soil in Niger. Treatments of the long-term field experiment were: control (–CR–F), mineral fertilizer only (–CR+F), crop residues only (+CR–F), and crop residues plus mineral fertilizer (+CR+F).In both years, total P uptake was similar for +CR–F and –CR+F treatments (1.6–3.5 kg P ha^-1), although available soil P concentration (Bray I P) was considerably lower in +CR–F (3.2 mg P kg^-1 soil) than in –CR+F (7.4) soil. In the treatments with mineral fertilizers (–CR+F; +CR+F), crop residues increased available soil P concentrations (Bray I P) from 7.4 to 8.9 mg kg^-1 soil, while total P uptake increased from 3.6 to 10.6 kg P ha^-1. In 1987 (with 450 mm of rainfall), leaf P concentrations of 30-day-old millet plants were in the deficiency range, but highest in the +CR+F treatment. In 1988 (699 mm), leaf P concentrations were distinctly higher, and again highest in the +CR+F treatment. In the treatments without crop residues (–CR–F; –CR+F), potassium (K) concentrations in the leaves indicated K deficiency, while application of crop residues (+CR–F; +CR+F) substantially raised leaf K concentrations and total K uptake. Leaf concentrations of calcium (Ca) and magnesium (Mg) were hardly affected by the different treatments.In the topsoil (0–30 cm), root length density of millet plants was greater for +CR+F (6.5 cm cm^-3) than for +CR–F (4.5 cm cm^-3) and –CR+F (4.2 cm cm^-3) treatments. Below 30 cm soil depth, root length density of all treatments declined rapidly from about 0.6 cm cm^-3 (30–60 cm soil depth) to 0.2 cm cm^-3 (120–180 cm soil depth). During the period of high uptake rates of P (42–80 DAP), root colonization with vesicular-arbuscular mycorrhizal (VAM) fungi was low in 1987 (15–20%), but distinctly higher in 1988 (55–60%). Higher P uptake of +CR+F plants was related to a greater total root length in 0–30 cm and also to a higher P uptake rate per unit root length (P influx). Beneficial effects of crop residues on P uptake were primarily attributed to higher P mobility in the soil due to decreased concentrations of exchangeable Al, and enhancement of root growth. In contrast, the beneficial effect of crop residues on K uptake was caused by direct K supply with the millet straw.     

Silicon accumulation and water uptake by wheat

Silicon (Si) content in cereal plants and soil-Si solubility may be used to estimate transpiration, assuming passive Si uptake. The hypothesis for passive-Si uptake by the transpiration stream was tested in wheat (Triticum aestivum cv. Stephens) grown on the irrigated Portneuf silt loam soil (Durixerollic calciorthid) near Twin Falls, Idaho. Treatments consisted of 5 levels of plant-available soil water ranging from 244 to 776 mm provided primarily by a line-source sprinkler irrigation system. Evapotranspiration was determined by the water-balance method and water uptake was calculated from evapotranspiration, shading, and duration of wet-surface soil. Water extraction occurred from the 0 to 150-cm zone in which equilibrium Si solubility (20°C) was 15 mg Si L^–1 in the A_p and B_k (0–58 cm depth) and 23 mg Si L^–1 in the B_kq (58–165 cm depth).At plant maturity, total Si uptake ranged from 10 to 32 g m^–2, above-ground dry matter from 1200 to 2100 g m^–2 and transpiration from 227 to 546 kg m^–2. Silicon uptake was correlated with transpiration (Si_up=–07+06T, r²=0.85) and dry matter yield with evapotranspiration (Y=119+303ET, r²=0.96). Actual Si uptake was 2.4 to 4.7 times that accounted for by passive uptake, supporting designation of wheat as a Si accumulator. The ratio of Si uptake to water uptake increased with soil moisture. The confirmation of active Si uptake precludes using Si uptake to estimate water use by wheat.     

Root effects on soil water and hydraulic properties

Plants can affect soil moisture and the soil hydraulic properties both directly by root water uptake and indirectly by modifying the soil structure. Furthermore, water in plant roots is mostly neglected when studying soil hydraulic properties. In this contribution, we analyze effects of the moisture content inside roots as compared to bulk soil moisture contents and speculate on implications of non-capillary-bound root water for determination of soil moisture and calibration of soil hydraulic properties. In a field crop of maize (Zea mays) of 75 cm row spacing, we sampled the total soil volumes of 0.7 m × 0.4 m and 0.3 m deep plots at the time of tasseling. For each of the 84 soil cubes of 10 cm edge length, root mass and length as well as moisture content and soil bulk density were determined. Roots were separated in 3 size classes for which a mean root porosity of 0.82 was obtained from the relation between root dry mass density and root bulk density using pycnometers. The spatially distributed fractions of root water contents were compared with those of the water in capillary pores of the soil matrix. Water inside roots was mostly below 2–5% of total soil water content; however, locally near the plant rows it was up to 20%. The results suggest that soil moisture in roots should be separately considered. Upon drying, the relation between the soil and root water may change towards water remaining in roots. Relations depend especially on soil water retention properties, growth stages, and root distributions. Gravimetric soil water content measurement could be misleading and TDR probes providing an integrated signal are difficult to interpret. Root effects should be more intensively studied for improved field soil water balance calculations. Presented at the International Conference on Bioclimatology and Natural Hazards, Pol’ana nad Detvou, Slovakia, 17–20 September 2007.     

Deposition of ammonia to the forest floor under spruce and beech at the Höglwald site

Laboratory and field measurements of the flux of ammonia to forest floor canopies of spruce and beech stands at the Höglwald site in southern Bavaria are reported. Measurements were performed with an open chamber method. A linearity between ammonia concentration and ammonia flux from the atmosphere to the ground floor canopy was detected. Deposition of ammonia showed no saturation even at air concentrations up to 50 g NH₃ m^–3 air. Temperature, water content and the moss layer of the ground floor canopy had a minor influence on the deposition velocity in laboratory experiments. Deposition velocity of ammonia was higher to the spruce (1.3 cm s^–1), and limed spruce ground floor canopy (1.17 cm s^–1) compared to the beech stand (0.79 cm s^–1). In field studies, a diurnal course of the deposition velocity was detected with highest velocities in midday and minor during night times, but not in the climatic chamber. The flux of ammonia to the ground floor canopy was estimated of app. 10 kg N ha^–1 yr^–1 for the soil under spruce, 9 kg N ha^–1 yr^–1 for the limed spruce and 6 kg N ha^–1yr^–1 for the soil under beech. The fluxes are interpreted as fluxes from the atmosphere to the ground canopies of the stands.     

Effect of Rural Sewage Irrigation Regime on Water-Nitrogen Utilization and Crop Growth of Paddy Rice in Southern China

Reclaimed water irrigation has become an effective mean to alleviate the contradiction between water availability and its consumption worldwide. In this study, three types of irrigation water sources (rural sewage’s primary treated water R1 and secondary treated water R2, and river water R3) meeting the requirements of water quality for farmland irrigation were selected, and three types of irrigation water levels (low water level W1 of 0–80 mm, medium water level W2 of 0–100 mm, and high water level W3 of 0–150 mm) were adopted to carry out research on the influence mechanismS of different irrigation water sources and water levels on water and nitrogen use and crop growth in paddy field. The water quantity indicators (irrigation times and irrigation volume), soil ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃⁻-N), rice yield indicators (thousand-grain weight, the number of grains per spike, and the number of effective spikes), and quality indicators (the amount of protein, amylose, vitamin C, nitrate and nitrite content) of rice were measured. The results showed that, the average irrigation volume under W3 was 2.4 and 1.9 times of that under W1 and W2, respectively. Compared with R3, the peak consumption of rice was lagged behind under R1 and R2, and the nitrogen form in 0–40 cm soil layers under rural sewage irrigation was mainly NH₄⁺-N. The changes of NO₃⁻-N and NH₄⁺-N in the 0–40 cm soil layer showed the trend of declining and then increasing. The water level control only had a significant effect on the change of NO₃⁻-N in the 60–80 cm soil layer. Both irrigation water use efficiency and crop water use efficiency were gradually reduced with the increase of field water level control. The nitrogen utilization efficiency under rural sewage irrigation was significantly higher than that under R3. Compared with the R3, rural sewage irrigation could significantly increase the yield of rice, and as the field water level rose, the effect of yield promotion was more obvious. It was noteworthy that the grain of rice under R1 monitored the low nitrate and nitrite content, but no nitrate and nitrite was discovered under R2 and R3. Therefore, reasonable rural sewage irrigation (R2) and medium water level (W2) were beneficial to improve nitrogen utilization efficiency, crop yield and crop quality promotion.

     

玉米农田蒸散过程及其对气候变化的响应模拟

应用基于生理生态学过程的EALCO模型,对玉米农田生态系统的蒸散(ET)过程进行了模拟,在模型检验基础上,使用该模型模拟了玉米农田生态系统ET过程对未来气候变化的响应。结果表明,EALCO模型中能量与水过程的动态耦合机制使模型能够较好地模拟农田蒸散过程,基于涡度相关法的观测值与模型模拟值在小时、日尺度上均吻合较好,模型可以解释67%的日蒸散的变化特征。对土壤蒸发与冠层蒸腾的分别模拟显示,生长季土壤蒸发约占ET的36%。温度的升高会引起ET与冠层蒸腾的增加,同时土壤蒸发减少;ET对降水减少的响应较为敏感,主要表现在土壤蒸发的下降。大气CO2浓度升高对冠层蒸腾影响显著,该情景下冠层蒸腾下降幅度最大。研究所假设的2100年气候情景下,该农田生态系统生长季蒸散将减少,然而相对于降水的减少而言,蒸散的减少量较小,即水分支出项相对增加,因此,发生土壤水分匮乏的可能性加大,这可能会加剧该地区的暖干化趋势,给作物产量及生态环境带来威胁。     

Barley yield under saline water cultivation

Summary In a microplot experiment conducted during the winter seasons of 1979–80 and 1980–81 on a sandy loam soil in the semi-desert tract, the accumulation of salts was found to be highest in March after harvest of the barley crop grown with saline water of EC values ranging from 2.2 to 24 mmhos/cm. The average EC of saturation extract of the surface soil layer (0–15 cm) was 0.79 times that of the applied irrigation water at the time of crop harvest, however, accumulated salts of the winter season were leached by the following monsoon rains. The average SAR of saturation extract of soil was 1.5 times that of the irrigation water in March but quite low in November. Highly significant correlations, (+0.90 to 0.99) at the post irrigated period between ECse of soils and EC of waters and SARse of soils and SAR of waters have been observed. Barley could be grown economically with irrigation water upto EC 16 mmhos/cm; however an average reduction in grain yield or not more than 43.5% compared to the yield under irrigation with tube well water of EC 2.2 mmhos/cm, was obtained. The starch, N and P contents decreased and that of K and Na increased in the grain with the use of saline waters. The performance of DL-85 variety was best and its K/Na ratio was also higher than that of other tested varieties.     

Denitrification in the top soil of managed grasslands in The Netherlands in relation to soil type and fertilizer level

The objective of this investigation was to determine how free-air carbon dioxide enrichment (FACE) of cotton (Gossypium hirsulam L.) affects root distribution in a natural soil environment. For two years cotton was grown on a Trix clay loam under two atmospheric CO₂ concentrations (370 and 550 μmol mol⁻¹) and two water treatments [wet, 100% of evapotranspiration (ET) replaced and dry, 75% (1990) and 67% (1991) of ET replaced] at Maricopa, AZ. At early vegetative and mid-reproductive growth, 90 cm soil cores were taken at 0,0.25, and 0.5 m perpendicular to row center; root variables were ascertained at three 30 cm depth increments. The effect of water stress alone or its interaction with CO₂ on measured variables during both samplings were rare and showed no consistent pattern. There was a significant CO₂ × position interaction for root length density at the vegetative stage (both years) and reproductive stage (1990 only); the positive effects of extra CO₂ were more evident at interrow positions (0.25 and 0.5 m). A CO₂ × depth × position interaction at the vegetative phase (1990) indicated that FACE increased root dry weight densities for the top soil depth increment at all positions and at the middle increment at the 0.5 m position. Similar trends were seen at the reproductive sampling for this measure as well as for root length density at both sample dates in 1990. In 1991, a CO₂ × depth interaction was noted at both periods; CO₂ enhancement of root densities (i.e., both length and dry weight) were observed within the upper and middle depths. Although variable in response, increases for root lineal density under high CO₂ were also seen. In general, results also revealed that the ambient CO₂ treatment had a higher proportion of its root system growing closer to the row center, both on a root length and dry wight basis. On the other hand, the FACE treatment had proportionately more of its roots allocated away from row center (root length basis only). Results from this field experiment clearly suggest that increased atmospheric CO₂ concentration will alter root distribution patterns in cotton.     

Influence of mulching on the pattern of growth and water use by spring wheat and moisture storage on a fine textured soil

Eight tonnes ha^–1 of stubble were used to mulch spring wheat (Triticum aestivum) on a fine textured soil with the aim of controlling both transpiration and soil evaporation during the wet pre-anthesis phase to increase moisture supply during grain filling in the eastern wheatbelt of Western Australia. Mulching reduced leaf area per plant by reducing the culm number; consequently the green area index was reduced. Reduced culm number was associated with low soil temperature which at 50 mm depth averaged 7°C lower under the mulched crop relative to the control crop in mid-season. The smaller canopies of the mulched crop used 15 mm less water than those of the control before anthesis; this difference in water-use was due equally to reduced transpiration and soil evaporation. However, the mulched crop was unable to increase ET during grain filling, a response associated with the persistence of low soil temperature for most of the growth period. Hence, total ET for the season was significantly lower (18 mm) under the mulched crop than the control crop. At harvest, mulching did not have significant effects on total above-ground dry matter and grain yields, but it increased water use efficiency for grain yield by 18%, grain weight by almost 17% and available moisture in both uncropped and cropped plots by an average of 43 mm.To determine whether there was any residual effects of soil treatment on moisture storage during the summer fallow period, soil moisture was monitored both in cropped plots and uncropped plots, that were either mulched or unmulched during the growing season, from harvest in October 1988 until next planting in June 1989. Available moisture at next planting was correlated with moisture storage at harvest despite the differences in run-off, soil evaporation and fallowing efficiency (increase in moisture storage as a percentage of rainfall) between treatments during fallowing. Therefore, the mulched treatments had more moisture available (30 mm), mostly as a result of less water use during cropping in the previous growing season, than the unmulched treatment.The study shows that mulching may be used to restrain both transpiration and soil evaporation early in the season to increase availability of soil moisture during grain filling. Secondly, mulching during the previous growing season had little effect on soil moisture during the summer fallow period, however, the moisture saved by mulching during cropping was conserved for the following season. These results indicate the importance of evaluating mulching of winter crops in terms of crop yield in the subsequent growing season as well as in the current season in which the soil was treated.Abbreviations D through drainage - DAS days after sowing of the crop on 31 May 1988 - DM dry matter produced in the above-ground portion of the crop (kg ha^–1) - E₀ evaporation from Class A pan (mm) - E_s evaporation from uncropped soil (mm) - E_sc evaporation from soil beneath the wheat canopy (mm) - ET evapotranspiration (mm) - FE fallowing efficiency (gain in soil moisture storage/rainfall) - GAI green area index (area of green vegetation per unit land area) - GWUE water-use efficiency for grain production (grain yield/total ET, kg ha^–1mm^–1) - K extinction coefficient (see equation 1) - RO run-off of moisture from soil surface during/following rainfall (mm) - SM available soil moisture (mm) at harvest (SMh) or at planting (SMp) - WUE water-use efficiency for total above-ground dry matter yield (see GWUE)