Estimating the substrate water status using capacitance measurements

The suitability of capacitance probes for measuring the actual variations in substrate water content in container-grown ornamental species (Lawson cypress) was examined. The probes were installed in the plant containers. Weighing measurement data on water loss was used to assess the actual changes in substrate water content (plant water use). In an additional test, an evaluation of temperature sensitivity of the capacitance probe was performed under laboratory conditions. The probe was placed in a container containing the growing medium (peat substrate) with a defined (stable) moisture content. The substrate temperature was modified and the changes in probe output were recorded. The experiment demonstrated the existence of the effect of temperature on the quality of soil moisture measurements conducted with the capacitance method. The accuracy of the results obtained from measurements with dielectric sensors in relation to the data obtained by means of weighing platforms depended largely on the temperature profile of the measured medium. It was demonstrated that temperature variations explained 99% of the observed differences in the results of moisture content measured with the capacitance method. Due to the fact that there is no possibility of developing universal factors (for different sensors and substrates) for correcting the influence of temperature, this relationship should be defined independently for a given type of crop and the measuring system available

An hourly reference evapotranspiration model as a tool for estimating plant water requirements

The usefulness of estimating hourly reference evapotranspiration for assessing the water requirements of plants over a 24-hour period was determined in the study. The values of hourly (ET0,h) and daily (ET0,d) evapotranspiration were calculated using the Penman-Monteith (PM) model. The daily ET0 was calculated automatically by the meteorological station, and the evapotranspiration values for individual hours were calculated using spreadsheet software. To verify the values of evapotranspiration calculated with these two approaches in relation to the actual water needs of grass, lysimetric measurements were performed. Additionally, substrate moisture content and temperature were measured using capacitance probes. The values of evapotranspiration estimated with the hourly PM model were higher than those determined with the daily model. An accuracy of the hourly model in relation to the data measured with a weighing lysimeter depended largely on the quality of the reproduction of meteorological parameters at the site of the crop. Observed underestimation of the actual daily evapotranspiration was presumably due to the use of air temperature values in the calculations (measured at a height of 2 m by the weather station). During strong solar radiation the air temperature was much lower than the temperature of the upper layer of the substrate in the weighing lysimeter. Reference evapotranspiration was recalculated by introducing into the hourly PM model the measured values of substrate temperature. After taking into consideration the higher temperatures, the calculated values of evapotranspiration increased, and the regression model took the form: y = 1.01x + 0.014 (R2 = 0.90), which proves the proportionality of the calculated and measured (actual water needs determined with the weighing lysimeter) data. Reliable data on the hourly variations in evapotranspiration over a 24-hour period can be a great tool for use in controlling the irrigation of plants grown in a limited volume of substrate

Estimation of water consumption by strawberry plants cultivated under greenhouse conditions

The experiment was conducted during two seasons (2002, 2003) t o investigate water consumption by three strawberry cultivars (‘Elsanta’, ‘Elkat’, ‘Salut’) grown under greenhouse conditions. Strawberry plants were grown in pots filled with a peat substrate. The pots were placed on top of glass containers filled with a nutrient solution. Each pot was connected with the container below by two pieces of water absorbing material immersed in the nutrient solution. The amount of the nutrient solution taken up by the plants was recorded every day. The highest water consumption was recorded for ‘Elsanta’, and the lowest one for ‘Salut’ plants. Water use efficiency calculated as a ratio of the total amount of water consumed by the plant and the size of the fruit crop produced ( cm 3 H 2 O g - 1 of fruit) was similar for the cultivars ‘ Salut’ and ‘Elsanta’. The highest level of water consumption recorded for ‘Elsanta’ plants indicates that it was caused by the high production potential of this cultivar

Ocena przydatnosci podloza kokosowego do bezglebowej uprawy truskawki [Fragaria x ananassa Duch.]

W jednorocznych badaniach określono możliwość zastosowania podłoża kokosowego w uprawie truskawki pod osłonami. Ocenie poddano właściwości fizyczne podłoża kokosowego i torfu oraz wpływ różnych poziomów nawożenia na wzrost i owocowanie roślin truskawki odmiany Elsanta. Wyniki doświadczenia wykazały, że właściwości fizyczne zarówno torfu, jak i kokosu są odpowiednie dla prawidłowego wzrostu truskawki. Generalnie większy i o lepszej jakości plon uzyskano z roślin rosnących na podłożu torfowym. Nie stwierdzono negatywnego skutku obniżenia dawki nawożeniowej na wzrost roślin i wielkość plonu uzyskanego w trakcie doświadczenia. Obserwacje te sugerują możliwość ograniczenia nawożenia roślin truskawki rosnących na podłożach bezglebowych, co może mieć istotne znaczenie dla obniżenia kosztów produkcji owoców i zmniejszenia zanieczyszczenia środowiska naturalnego.The possibility of using coco substrate in production of strawberry plants under greenhouse conditions and the effect of different fertilizer rates on growth and fruiting of these plants were examined in one year study. Obtained results showed that physical properties of peat and coco substrate were adequate for growth of strawberries. Plants grown in peat produced more fruits and their quality was better compared to these from coco substrate. The lack of negative effect of lower nutrient supply, suggests the possibility of reduction of rates of mineral fertilizers in soilless strawberry production systems, decrease of production costs and pollution of environment

A new approach to the method of drawing the Gaussen-Walter climate diagram

In traditional climate diagrams a fixed coefficient (α) between temperature and precipitation has been adopted. It has been shown, however, that such an approach does not correctly describe the conditions of the climatic balance in Poland for the entire growing season. In this paper, a different solution to this problem is proposed - the introduction of a variable coefficient for individual months. The analysis of patterns of climatic variables over the year supports the hypothesis that in order to estimate ETo only by means of mean air temperature (ETo = α·T), the coefficient α should be variable for the individual months of the vegetative period. The values of the coefficient were empirically determined for use in calculating daily and monthly ETo. The newly proposed coefficients α were different from those determined with the standard climate diagram (published by Walter, Lieth 1967). The introduction of the variable value α into the computational model markedly improved the quality of the estimation of ETo. The mean bias errors determined for the estimation of ETo on the basis of temperature and the changing value of α were considerably lower than for the estimation of ETo with a fixed value of α. This provides the possibility of a more accurate presentation of periods of both excess and shortage of precipitation

Effect of water deficit on gas exchange parmeters, growth and yield of two strawbery cultivars grown under greenhouse conditions

W doświadczeniu określono wpływ deficytu wody w podłożu na wybrane parametry fizjologiczne, wzrost i plonowanie roślin dwóch odmian truskawki uprawianych w szklarni. Niedobór wody w podłożu (-30 kPa) był utrzymywany poprzez ograniczenie nawadniania. W doświadczeniu wykazano zróżnicowanie reakcji dwóch odmian truskawki na suszę. W warunkach stresu u roślin odmiany ‘Sonata' stwierdzono mniejsze zahamowanie rozwoju systemu korzeniowego oraz powierzchni liściowej w porównaniu z ‘Elsantą'. Na podstawie pomiarów parametrów fizjologicznych (natężenia fotosyntezy i transpiracji), których stosunek wyraża efektywność wykorzystania wody, wykazano, że rośliny odmiany ‘Sonata' charakteryzują się sprawniejszą regulacją stosunków wodnych. W warunkach optymalnego zaopatrzenia w wodę rośliny obu odmian wydały plon podobnej wielkości. Niedobór wody spowodował większe ograniczenie plonowania w przypadku roślin odmiany ‘Elsanta'.The response of two strawberry cultivars (‘Elsanta’, ‘Sonata’) to drought was examined by evaluating the yield and selected morphological and physiological parameters. Plants were subjected to two different water regimes: optimalirrigation (control), and reduced irrigation (water potential in the growing medium was maintained at a level -30 kPa, stress treatment). Genotypes differed in their response to water deficiency. Cultivar ‘Sonata’ presented high rates of net photosynthesis with high value of water use efficiency (a ratio of photosynthetic rate to transpiration rate) under water shortage conditions. Drought stress reduced leaf area in all cultivars, but root development was retarded only in ‘Elsanta’. Under water deficiency conditions reduction of yield was higher for ‘Elsanta’. ‘Sonata’ appeared to be more drought resistant which was reflected by both growth and yield parameters

Influence of supplementary lighting with high pressure sodium and LED lamps on growth, yield and photosynthetic activity of strawberry plants

Rośliny truskawki (odmiany „Elsanta” „Grandarosa”) uprawiane w szklarni w okresie zimowo-wiosennym (luty-maj) doświetlano przy pomocy lamp sodowych lub LED (diody emitujące światło czerwone, niebieskie oraz w zakresie bliskiej podczerwieni). Kombinację kontrolną stanowiły rośliny rosnące w warunkach naturalnego światła. Prowadzono pomiary intensywności wymiany gazowej oraz natężenia zielonej barwy liści (względna zawartość chlorofilu). Określono plonowanie roślin, a po zakończeniu doświadczenia wykonano analizę budowy morfologicznej roślin, mierząc masę i powierzchnię liści, masę korzeni oraz średnicę korony. Stwierdzono zróżnicowaną reakcję ocenianych odmian na doświetlanie. Zastosowane światło LED spowodowało zwiększenie natężenia fotosyntezy roślin odmiany „Grandarosa”. Rośliny te charakteryzowały się także intensywniejszym wzrostem i większym plonowaniem w porównaniu do roślin niedoświetlanych. W przypadku odmiany „Elsanta” przebieg procesów fizjologicznych, wzrost i plonowanie roślin nie były uzależnione od zastosowanego doświetlania.The objective of the study was to evaluate the physiological response and growth of strawberry plants grown under different light treat-ment. During cultivation period (February-May), the plants (two cultivars: ‘Elsanta’, ‘Grandarosa’) received supplemental artificial lighting provided by standard high-pressure sodium lamps or high-power solid-state lighting modules with red, blue and far red LEDs. Quantum irradiance in the both combinations was maintained at the same level. The third group of plants (control combination) was grown under the natural light (without sup-plemental lighting). The following measurements were taken: photosynthetic rate, leaf greenness index (relative chlorophyll content), fruit yield and the most important morphological parameters (fresh weight of plant organs, leaf surface area, crown diameter). The results showed that supplemental illumi-nation using LED light source affected photosynthesis (higher rates), growth (higher foliage weight and area) and productivity of ‘Grandarosa’ straw-berry plants. On the opposite, no significant effect of supplemental artificial lighting on performance of ‘Elsanta’ plants was recorded. The obtained results showed that LED lamps could be used in greenhouse lighting systems. However, much work still has to be done to optimize lighting spectrum of LED modules for the cultivation of the specific crop species and cultivars