•We review components of the water balance for Australian grain crops.•For wheat, on average 38% of evapotranspiration was lost to direct soil evaporation.•No evidence for increased transpiration at ...the expense of soil evaporation.•Transpiration efficiencies vary within crops after accounting for vapour pressure deficit.•More robust seasonal estimates of crop transpiration efficiency are required.
Australian agriculture is dominated by rainfed cropping in environments where evaporative demand greatly exceeds annual rainfall. In this paper we review field measurements of crop transpiration and bare soil evaporation under rainfed grain crops, and crop transpiration efficiencies. Crop transpiration is typically calculated from the difference between evapotranspiration and bare soil evaporation, however, while the former is readily measured, the latter is difficult to obtain. For wheat we found only 19 studies which measured the critical water balance parameters of bare soil evaporation and crop transpiration in Australia, and very many fewer for other crops. From the studies reported for wheat, on average 38% of evapotranspiration was lost to direct soil evaporation. Data for other crops are insufficient to ascertain whether they are similar or different to wheat in terms of the relative contributions of Es and T to the water balance. Although it may have occurred in practice, we can find no field measurements of the crop water balance to demonstrate an increase in crop transpiration at the expense of bare soil evaporation as a function of improvements in agronomic practices in recent decades.
Although it is thought that crop transpiration efficiencies are primarily a function of vapour pressure deficit, transpiration efficiencies reported in the literature vary considerably within crops, even after accounting for vapour pressure deficit. We conclude that more reliable estimates of crop transpiration efficiency would be highly valuable for calculating seasonal transpiration of field grown crops from shoot biomass measurement, and provide an fruitful avenue for exploring water use efficiency of grain crops.
Agrometeorological department of Meteorological Office at Slovenian Environment Agency (ARSO) is a key provider of agrometeorological service in Slovenia. Its major priority is to manage ...agrometeorological and phenological networks including providing guidelines for observers and maintenance of databases. Agrometeorological and phenological data are foundation for several tools and analyses which have been developed during the past decades for agricultural decision purposes. Recently, focus is on the crop water balance modelling with irrigation forecasts, drought monitoring, climate change impact scenarios and many others. After year 2006 special work emphasis is on coordination of Drought Management Center for South-eastern Europe hosted by ARSO. A set of information, tools and publications, bulletins is free available at the webpage and servers of ARSO with the aim to make smarter weather/climate related decisions in agriculture.
ABSTRACT The present work was performed by applying the principal component analysis, in order to compare the water needs of banana, mango, grape, sugarcane, maize and beans crops in different ...regions of the São Francisco river basin, aiming to identify the climate elements that most influence the reference evapotranspiration (ET0) in the locations of Pirapora-MG, Jaíba-MG, Barreiras-BA and Petrolina-PE. In addition, the locations with more similarities, according to the evaluated parameters, were verified by applying cluster analysis, and the equivalence relations between the studied crops were determined by integrating the parameters related to the climatic elements and the characteristics of crops and soils. Based on the principal components analysis, it was observed that the most significant climate elements for ET0 estimation were different for each place. The model with two components explained 90%, 88%, 95% and 97% of the total variance, respectively for the locations of Pirapora, Jaíba, Barreiras and Petrolina. Because it is in a semi-arid climate region, Petrolina showed high crop water needs, a behavior proven with the cluster analysis. The equivalence relations allowed comparing the water needs for the studied crops, providing, in general terms, a parameter comparison between the crops, and specifying which one will be more adequate depending on the water availability in the São Francisco basin.
Reference evapotranspiration (E T 0) is a major estimator for crop water requirements predicted by decision support systems for irrigation. However, the impact of different E T 0s on the predicted ...amount of water supply and counts of irrigation events has not been evaluated. Simulations of the Geisenheim Irrigation Scheduling (GS) for vegetable crops with two different E T 0s, P2-E T 0 and FAO56-E T 0, were evaluated to assess exemplarily the impact of E T 0s. The sensitivity of both E T 0s to local climate conditions was characterized through a random forest analysis, and a linear regression model was used to adjust the original GS by adapting K c-values to the exchange E T 0. For assessing the outcomes of GS irrigation decision, simulations of 173 individual cropping cycles including six vegetable crops over eight years were conducted. After adjusting P2-E T 0 K c-values to FAO56-E T 0 K c-values, there was no impact of the E T 0-model on the practical irrigation scheduling with GS. Finally, we discuss that any E T 0-model, if adjusted accordingly, might have little impact on similar irrigation systems and provide a method to exchange E T 0s.
To detect temporal and spatial variability of drought is one of the most challenging issues of drought monitoring in the specific country or region due to the fact that there is no standard ...definition of severity and duration of different types of drought. Crop water deficit (CWD) simulated by crop water balance model IRRFIB supplemented with some in-situ soil water measurements by Time-Domain Reflectometry (TDR) measurement technique are proposed as tools for local agricultural drought monitoring in this study. Moving to regional drought monitoring the main constraint represents data availability of different sources. Available global data sets are of assistance for preparing regional drought monitoring products. In the study two specific products designed for regional scale are described: preliminary maps of the SPI (Standardized Precipitation Index) and products generated by implementation of numerical weather prediction model. It seems to be a lot of potential in both products for a first overview of key meteorological parameters in the region. The development of drought in the year 2009 was under examination and also yearly results for different periods after 1971. Dry periods in the year 2009 heavily impacted cereals in Slovenia. Maize yield showed best agreement with crop water deficit (r = 0.65) and SPI on the time scale of six months for September (r = 0.61). SPI was not suitable for describing agricultural drought in the periods with higher evapotranspiration rate. For more agricultural oriented drought monitoring more indices should be included into the consideration.
Eden izmed večjih izzivov na področju monitoringa suše v določeni državi ali regiji je določanje časovne in prostorske variabilnosti suše, saj ne obstaja splošna definicija, ki bi določala intenzivnost in trajanje različnih tipov suše. V študiji predlagamo primanjkljaj vode pri rastlinah (CWD), simuliran z vodnobilančnim modelom IRRFIB in podprt z in-situ meritvami vode v tleh s TDR tehnologijo, kot primerno orodje za lokalno določanje kmetijske suše. Na širšem, regionalnem nivoju pa se pojavi ovira pri dostopnosti podatkov, zato si pri pripravi regionalnih produktov lahko pomagamo z globalnimi nizi. Opisujemo dve možnosti, primerni za regionalno skalo: preliminarne karte standardiziranega padavinskega indeksa (SPI) in produkte, ki jih generiramo z implementacijo numeričnega modela za napovedovanje vremena. Pri obeh se kaže velik potencial za prvi, splošni pregled nad stanjem glavnih meteoroloških parametrov v regiji. Za primer smo vzeli razvoj suše leta 2009 ter letne rezultate za različna obdobja po letu 1971. Leta 2009 so sušna obdobja hudo prizadela poljščine v Sloveniji. Pridelek koruze kaže najboljšo povezanost s primanjkljajem vode CWD (r = 0,65) in z indeksom SPI na šestmesečni časovni skali za september (r = 0,61). Indeks SPI se ni izkazal za primernega pri obravnavi obdobij z višjo stopnjo potencialne evapotranspiracije. Opozarjamo še na dejstvo, da bi bilo potrebno za bolj kmetijsko usmerjen monitoring suše vključiti več različnih indeksov.
Experiments are presented that test the relative importance, during ontogeny, of stomatal control and leaf area expansion to optimum seasonal water use in pearl millet (Pennisetum glaucum). These ...parameters play a key role in the compromise between plant growth and water saving under unpredictable conditions of semiarid environments. The response of growth and water use of crops to successive 15 d drought periods was measured under field conditions in Niger (West Africa). From emergence to anthesis, biomass partitioning to stems and panicles depended strongly on leaf area development. Water use was linearly related to green leaf area duration in well watered plots, but was reduced proportionally more than green leaf area in drought-affected plots. The relations of crop growth rate and transpiration efficiency to leaf area depended on ontogenetic changes in biomass partitioning. In P. glaucum, stomata play a dominant role in reducing crop water use under preanthesis drought, although this control becomes negligible after anthesis because of ontogenetic decline in the range of stomatal conductance. The rate of leaf senescence after anthesis is not drought-dependent.
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