With respect to ongoing discussions about the causes of energy imbalance and approaches to force energy balance closure, a method has been proposed that allows partial latent heat flux closure (Widmoser and Wohlfahrt, 2018). In the present paper, this method is applied to four measurement stations over grassland under humid and semiarid climates, where lysimeter (LY) and eddy covariance (EC) measurements were taken simultaneously. The results differ significantly from the ones reported in the literature. We distinguish between the resulting EC values being weakly and strongly correlated to LY observations as well as systematic and random deviations between the LY and EC values. Overall, an excellent match could be achieved between the LY and EC measurements after applying evaporation-linked weights. But there remain large differences between the standard deviations of the LY and adjusted EC values. For further studies we recommend data collected at time intervals even below 0.5 h. No correlation could be found between evaporation weights and weather indices. Only for some datasets, a positive correlation between evaporation and the evaporation weight could be found. This effect appears pronounced for cases with high radiation and plant water stress. Without further knowledge of the causes of energy imbalance one might perform full closure using equally distributed weights. Full closure, however, is not dealt with in this paper.

The commonly observed lack of energy balance closure at eddy covariance flux tower sites represents an outstanding problem in micrometeorology and significantly compromises the value of eddy covariance latent and sensible heat flux measurements. Here we used concurrent lysimeter and eddy covariance evapotranspiration measurements to correct for the energy imbalance attributable to the eddy covariance latent heat flux measurements (32%) and then, by assuming that the Bowen ratio is correctly quantified by the eddy covariance method, attributed the remainder of the energy balance to the sensible heat flux (10%) and the available energy (58%). We discuss our findings with respect to the ongoing discussion on the causes of the energy imbalance and approaches to force energy balance closure.

Elucidating the causes for the energy imbalance, i.e. the phenomenon that eddy covariance latent and sensible heat fluxes fall short of available energy, is an outstanding problem in micrometeorology. This paper tests the hypothesis that the full energy balance, through incorporation of additional independent measurements which determine the driving forces of and resistances to energy transfer, provides further insights into the causes of the energy imbalance and additional constraints on energy balance closure options. Eddy covariance and auxiliary data from three different biomes were used to test five contrasting closure scenarios. The main result of our study is that except for nighttime, when fluxes were low and noisy, the full energy balance generally did not contain enough information to allow further insights into the causes of the imbalance and to constrain energy balance closure options. Up to four out of the five tested closure scenarios performed similarly and in up to 53% of all cases all of the tested closure scenarios resulted in plausible energy balance values. Our approach may though provide a sensible consistency check for eddy covariance energy flux measurements.

Small weirs may control the groundwater level of drained fields in such a way that a balance between concerns of agriculture, flood prevention and water quality may be achieved. Based on a spreadsheet calculation, an easy to use software package is presented considering the interactions between precipitation, groundwater level, drain discharge, ditch runoff and weir action. Examples of calculation performed show the potential of flood prevention in different soils, the effect of different drain spacing and the influence of ditch maintenance on the operation of the entire system.

The Penman-Monteith (PMe) equation that estimates evaporation from leaf/canopy surfaces is based on a few approximations. Several authors discussed ensuing errors and suggested improvements. This paper reminds those discussions which ended in the early nineties. It compares linearized PMe- with non-linear iterative solutions and illustrates resulting deviations. It differentiates between deviations for daily and hourly evaporation rate estimates. The latter are found to be higher. It also demonstrates deviations obtained at two different altitudes above sea level. considering present tendencies to refine evaporation estimates for practical purposes and making use of easily available methods for solving non-linear equations this paper offers a new method to estimate evaporation.In a first step, a simple algebraic term, the surface temperature control sum, is introduced to find approximate differences between air and evaporating surface (leaf, canopy) temperatures. It suggests to concentrate research on the r(s)/r(a) ratio. A new formula is derived for estimating leaf/canopy surface temperatures for non-water stressed plants.In a second step, the estimates of temperature differences are used to calculate evaporation estimates. This two-step approximation leads to appreciably smaller errors as compared to the PMe-solution over the full range of input parameters of agro-meteorological relevance. It is, however, less accurate than some of methods proposed in literature, The method is meant for practical application in agricultural water management, (C) 2008 Elsevier B.V. All rights reserved.

Fresh water is a limited resource and its efficient use in agriculture represents a great challenge. The objective of the investigation was, to test a new subsoil irrigation technique for obtaining high grain yields and water use efficiency in comparison with furrow irrigation still used in Middle East. Clay pipes of the subsoil irrigation had a particular porosity which allowed a controlled diffusion of water out of the pipe into the soil. The pipes were imbedded into the soil at a depth of 0.3 m. The technique was tested in field trials with winter wheat (Triticum aestivum L.) in the 1992/1993 and 1993/1994 season under arid, continental climatic conditions of Persia on a representative silty loam soil. Plot size was 5 m(2).Yields were nearly twice as high under subsoil irrigation compared with furrow irrigation. With subsoil irrigation maximum grain yield (>10 Mg/ha) was already obtained with a N fertilizer rate of 50 kg N/ha. Water use efficiency (WUE) ranged from 1.64 to 3.34 in subsoil irrigation and from 0.46 to 1.2 g grain/kg water in furrow irrigation (p < 0.001). N release from soil was much higher under subsoil irrigation (111-216 kg N/ha) than under furrow irrigation (-11 to 33 kg N/ha). There were no significant differences between the irrigation techniques for the harvest index, single grain weight and the nitrogen fertiliser agronomic efficiency (AE). The apparent nitrogen recovery (ANR%) was high particularly in the subsoil irrigation treatments and decreased with N fertiliser rates. The question is raised whether this subsoil irrigation technique can be developed for the application on a large enough scale for crop production. (c) 2007 Elsevier B.V. All rights reserved.

Der Artikel enthält folgende Kapitel: Einleitung Wasserhaushaltsgleichung Niederschlag Verdunstung Bodenwasserhaushalt Abfluss Grundwasser Zitierte Literatur Abkürzungs- und Symbolverzeichnis Glossar

The underlying question of these investigations asked, how and to which extent rape plants react with transpiration and soil water uptake to different degrees of nitrogen fertilization. Therefore repeated campaigns with concurrent measurements of plant surfaces (leaves, stems, pods), diurnal courses of leaf transpiration and root length density of rape plants growing on heavily (240 kg ha(-1)), moderately, (120 kg ha(-1)), and nil N-fertilized plots of an experimental field in northern Germany were performed during two growing seasons. Additionally, matric potentials at different soil depths were measured. In the first year (1994) investigations were concentrated primarily on shoot area development and transpiration, whereas in the subsequent year (1995) root measurements were mainly undertaken. Also, the influence of soil management (ploughing, conservation tillage) was taken into consideration. The plots where the shoot measurements were carried out were ploughed in 1994 and rotovated in 1995. Matric potentials were measured in both years in ploughed soil and, for comparison, also in soils with conservation tillage. Shoot area index, as measure of the transpiratory capacity of the canopy, increased on ploughed soil and reached a maximum before flowering. Thereafter it decreased until harvest when the relative amount of green stems and pods was increasing. Then, the measured transpiration rate per pod surface area was equal to, or higher than, the transpiration rate per leaf surface area. Plant surface area was smaller in plots with conservation tillage and decreased generally with decreasing N-fertilization. Increasing plant surface area was joined by an increasing density of plant canopy. Light interception was thus highest in the plots receiving 240 kg N ha(-1). Although the shading effect may cause a reduction of transpiration per plant, the total plant mass per area generally resulted in a greater water loss from these plots. Roots reached at least 110 cm depth. Root length density was significantly higher in the upper 10-30 cm of soil than at greater depths. Root mass was smaller in soil with conservation tillage than in ploughed soil. Oscillations of soil matric potentials in the diurnal and long-term periods were highest in the upper 10 cm of soil. Here, they corresponded well with the cumulative diurnal transpiratory water loss. It is concluded that the soil water dynamics depends largely on the distribution of plant roots. As a result, rape plants did not change their specific transpiration capacity as a response to increased nitrogen fertilization. However, the transpiring plant surface and root length density increased the turnover rate of water by a higher plant density per plot. This effect was more pronounced in ploughed than in rotovated plots.

Within comparative studies on solute movement in tile drained agricultural fields in Schleswig-Holstein a bromide field test was conducted at two field sites. The soil of site 'Bokhorst' shows both spatial and profile heterogeneity with significant clay and silt contents (loam) whereas site 'Hohn' had a homogeneous particle size distribution within the profile with sand being the dominating particle fraction (sand) but with neglible spatial variability. Rainfall amount, drain dis charge and bromide concentrations in drain outflow were monitored over a 6 months period. A rapid response of drain discharge on rain events was observed for the loamy site but not for the sand. The simple water balance yielded +8.7 mm of drain discharge for site Bokhorst (loam) and -43 mm for the sandy site Hohn (sand).Largest bromide concentrations were detected shortly after chemical application at the loamy site. The bromide loss curve was characterized by simultaneous in- and decrease of flow rate and bromide concentrations. This solute behaviour was named 'event-dependent'. Bromide occurred in drain outflow at the sandy site not before 30 mm discharge and maximum concentrations were observed at the end of the monitoring period, Mass balance calculations revealed that 70.5% (loam) and 33% (sand) of the applied solute mass were transported from the fields via the tile drains. A two dimensional, advection dispersion equation based simulation model was applied to predict solute behaviour at site Bokhorst. Computed bromide concentrations were not in line with the observed preferential breakthrough curve. Consequences of preferential transport conditions in tile-drained field soils on surface water quality are briefly discussed, especially concerning the displacement of plantprotective agents and methodical difficulties.

The forest floor (total organic matter above the surface of the mineral soil) is an important interception storage for throughfall. Therefore, it must be considered in detailed water balances of forest. The objective in this paper is to present a method for measuring the forest floor percolation. It was developed within the framework of the interdisciplinary project Ecosystem research in the Bornhoyed lake region.A technique for permanent registration of mineral soil input and a vacuum control system for mini lysimeters and suction plates are described. The registration system has a resolution about 0,1 mm. Some figures illustrate the instrumentation, respectively measured row data and some results. Finally, the used materials, their properties and sources of supply are presented.

Use of the dew point method to determine matrix- and osmotic soil water potentials in pot cultures under different salt stress Water consumption of festuca rubra was investigated under different salt stress as measured by the dew point method. Water content of the soil, total tension and water consumption was measured daily. At the end of the growing season the low salt stress plants had used nearly completely all water available and were under water stress. Plants under medium salt stress reduced transpiration in time and showed highest water content in the soil and in the plants after growing season. For the high salt stress plants the total water potential remained low due to the osmotic component. Dew point measurements were compared with other methods (Cl-concentration; electric conductivity). A close correlation was found in all cases, demonstrating the usefulness of the dew point method.

Intercropping with maize (Zea mays L.) and common bean (Phaseolus vulgaris L.) is one of the widely used practices of producing food crops on smallholder farms in Sub-Saharan Africa (SSA). However, the knowledge on the options toward intensification of available practices in order to optimize systems productivity using intercrops is generally lacking. Therefore, this study evaluated the effects of intercropping, cropping seasons, and different varieties of common bean on productivity of the maize-common bean based intercrop through 5 cropping seasons from 2015 to 2017. Experimental site is located at 03°18 ′03.74′' S and 37°12′13.94′ E and an altitude of 956 m above sea level in the northern highlands of Tanzania. Hybrid maize Dekalb brand (DK 8031) and two varieties of common bean (improved Lyamungu 90 and local Mkanamna) were used. The treatments within a replicate were: (1) sole crops: (i) maize, (ii) local bean, (iii) improved bean, and (2) intercrops: (i) maize + local bean, (ii) maize + improved bean. Interaction and individual effects of cropping seasons (S) (periods of years – short and long rains), varieties of common bean (V), and cropping systems (C) (sole and intercrop) were studied. Results indicated that S × V interaction was significant on bean grain yield and 100-seed weight. Improved bean outweighed the local bean with grain yields ranging from 2.2–3.5 t ha-1 and 0.2–2.5 t ha-1, respectively. The effect of S was significant on all measured variables in beans and the effect of M was only significant on total biomass. Further, S significantly affected all measured variables in maize and grain yields ranged from 2.3–2.6 t ha-1. In maize, correlations were strong (r = 0.48*; P = 0.0325) between maize grain yield and ground coverage of leaf canopy measured 42–56 days after sowing. The land equivalent ratios (LERs) for maize intercropped with improved and local beans were 1.48 and 1.55, respectively but LER values did not differ significantly between bean varieties. In this study, both common bean varieties were sown simultaneously with the maize, which might have resulted in their differential performance. It is recommended that studies are conducted to evaluate time of introducing this legume crop to a maize system such as early sowing, sowing mid in the season after a maize crop is well established, and sowing late in the season when the leaves in maize plant have started to senesce.