Browsing by Subject "Fertigation"

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Bedarfsgerechte Stickstoffernährung von Hopfen (Humulus lupulus L.) durch Düngesysteme mit Fertigation
(2021) Stampfl, Johannes; Ebertseder, Thomas
In terms of quantity, nitrogen is the most important and most yield limiting plant nutrient in hops (Humulus lupulus L.), whereby excess nitrogen not taken up by the hop plant is subject to various loss processes. Despite that, little is known about the exact effects of an N supply varying in rate and timing for the hop varieties and cultivation systems currently used in the Hallertau, the worlds most important hop-growing region. In the Hallertau, the required amount of nitrogen is largely supplied by surface spreading of granulated N fertilizers, whereas in semi-arid growing regions, high proportions are applied via irrigation water (fertigation). The aim of this thesis was to examine nitrogen fertilization systems with fertigation under the conditions in the Hallertau region with regard to a nitrogen nutrition that is based on the hop plant’s needs. Therefore, four research questions with different sub-aspects have been formulated, as explained below. From 2017 to 2019 the experimental research and the acquisition of empirical data has been conducted in various field trials consisting of three trial series examining the most important hop varieties at different locations. Apart from a variation in rate and timing of N fertilization, different fertilizer application forms (surface application of granulated fertilizer and above- or below-ground fertigation) have also been examined. In addition to the determination of yield, quality and N-uptake at the time of harvest, further analysis methods such as the 15N-Tracer-Technique, chlorophyll value measurements (SPAD-Meter) or passive reflection measurements were used in individual field trials to depict the N-uptake and N-distribution in different parts of the plant. a) Which effects have different nitrogen treatments varied in rate and timing? These studies found that the hop plant absorbs more than two thirds of the total amount of nitrogen over a period of 7 to 8 weeks between early June and end of July - during formation of main biomass. Despite the fact that only a low amount of nitrogen is accumulated in the plant prior to this stage, the varieties Perle and Tradition showed that a nitrogen deficit in early growth stages until end of May already leads to a decrease of yield potential. This is due to a change in the variety-characteristic formation of lateral shoots (side arms) - the later the application of nitrogen, the greater the formation of side arms was reduced, starting from the bottom to higher plant sections. Consequently, a nitrogen fertilization solely based on the hop plant’s N uptake curve cannot be recommended, neither regarding yield formation nor nitrogen utilization. Instead, an early application of the first nitrogen treatment in April is of vital importance for early maturing varieties such as Perle and Tradition. Late maturing varieties like Herkules show a higher potential of compensation due to prolonged growth phases which enables a higher adaption of N-Fertilization to the plant’s N uptake curve. The ideal amount of nitrogen fertilization with regard to yield optimization has been determined by the growth pattern - depending on variety, weather conditions and location - and therefore by the N uptake, the supply of mineral nitrogen in the soil as well as the location-specific N mineralization potential. A reduction of the nitrogen fertilization to a level significantly below the plant’s N uptake not necessarily led to a limitation of biomass and yield formation in the same year, however, it resulted in an accelerated ripening and a negative impact on external cone quality. Furthermore, it showed that the storage of nitrogen in specific storage roots declines if N levels are significantly reduced, leading to lower vitality as well as limited plant development and yield formation in the following year. With regard to the hop plant’s perennial properties as well as the goal to achieve a demand-oriented nitrogen nutrition of the hop plant it is also necessary to supply the storage roots with enough nitrogen. With respect to valuable contents of alpha acid it has been found that high N supply levels during the stage of alpha acid synthesis (starting from early August) can result in a reduction of alpha acid concentration in the variety Herkules. This decrease can be caused by late and excessive N fertilization as well as by high mineral N contents in the soil. However, this effect has not been observed in the aroma varieties Perle and Tradition. b) Is it possible to determine the current nitrogen nutritional status through non-invasive methods? The measurement of the chlorophyll value with a SPAD-Meter on the lower leaves of the main shoot generally reflected the N content and N supply status of the hop plant. However, short-term changes in the N nutritional status could not be recorded with sufficient accuracy at this measuring point, especially not during the stage of main biomass formation, since increased proportions of the applied nitrogen were transported to higher plant sections, as was shown by the use of 15N. Regarding the determination of threshold values a classification of the plant development into before, during and after main biomass formation independent of the measuring point, is considered appropriate, since the chlorophyll value correlates with the plant’s development stage. Vegetation indices, calculated on the basis of reflectance spectra, represent not only the N content but also the actual N uptake of the crop, which is why passive reflectance measurement methods have a higher informative value with regard to the current N supply status of the plant compared to chlorophyll value measurements. Therefore, this technology could be used to achieve a site-specific optimization of rate and timing of N fertilization and thus a more demand-oriented nitrogen nutrition of the hop plant in the future. c) What are the effects of surface and subsurface drip irrigation? In the period from 2017 to 2019, additional irrigation of the aroma variety Perle on sandy soil led to a stabilization of the agronomic parameters cone yield and alpha acid content every year. In addition, irrigation also achieved an improvement of nitrogen utilization. Compared to subsurface systems, surface drip irrigation achieved a higher efficiency if the horizontal water distribution was limited by hydraulic soil properties. It was shown that this is due to the fact that the majority of the hop plant’s fine root system is located in the hill formed along the hop rows and the soil layers beneath it. d) What are the effects of a nitrogen nutrition via irrigation water? A system comparison was made between N fertilization systems with fertigation and a solely granulated N application. The use of fertigation resulted not only in an improvement of cone yield and alpha acid content, but also in an increase of the plants nitrogen uptake and a reduction of Nmin content in the soil, which is also associated with a reduction of the risk of nitrate leaching into the groundwater. Fertilization systems with fertigation achieved a higher nitrogen utilization especially at low N-fertilization rates. If two thirds of the total amount of nitrogen were applied via irrigation water, the concentration over a 6-week period proved to have a positive impact on all analyzed varieties, especially under conditions of a limited N supply, since a higher proportion of N has been applied during main biomass formation and the stage of lateral shoot growth. For an efficient N-fertilization with fertigation the application should take place between mid-June and late July while no significant amounts of nitrogen should be applied after early August. For early maturing varieties such as Perle and Tradition, there is a risk of a late N application as it is hardly possible to lay out the drip tubes before the 25th week of the year. Therefore, in early maturing varieties, a higher proportion of N should be applied in earlier growth stages while the amount of N applied via fertigation should be less than two-thirds of the total amount of N fertilizer. A substantial advantage of fertilization systems with fertigation is that nitrogen applied via the irrigation water is immediately absorbed by the plants, which allows an effective short-term intervention in the plant’s nitrogen nutrition. On the basis of a reliable recording of the current N supply status with sensors during the main growth stage, fertigation could be used to adjust the N fertilization in order to achieve a site-specific and demand-oriented nitrogen nutrition of the hop plant.
Spektralphotometrische Bestimmung des pflanzenverfügbaren Nitrats in der Bodenlösung : Entwicklung einer in-situ Messmethode zur Optimierung der Fertigation im intensiven Gemüsebau
(2015) Mayer, Stephan; Müller, Torsten
For many specialized cultivations, mainly in intensive horticulture, a slight N-deficiency may dramatically reduce crop quality and yield. Hence, especially in this case, fertilizer is often applied in surplus. Compared to the real N-demand of a crop, this results in a large investment in fertilizer and may also promote nitrogen loss due to leaching. At many sites, the consequences of this are nitrate contaminated ground and surface water. An in-situ method for the continuous determination of the actual and plant-available nitrate content in soil solution, which may be fundamental for adapted and culture specific fertilization, has not yet been created for practical use in horticulture. Such a method would minimize excessive nitrate loads, reduce fertilizer use as well as omit labor required for soil sampling for Nmin determination. The aim of this thesis is to develop such an in-situ method. For this purpose, nitrate was detected and quantified in soil solution by ultraviolet spectrophotometry. Based on these measurements and a comparison with the N-demand of the chosen crop, an adapted fertilization plan was established. Recovery of the necessary soil solution was carried out in the field with the aid of suction cups, which were connected to a vacuum system, which directed the solution to a measuring cell where the spectrophotometric measurement was performed. The data was collected and evaluated on an external server. After the calculation of the actual nitrate concentration, based on the spectral data, and comparing them to the N-demand, the need and amount of fertilization was determined. This process is performed automatically. Based on numerous lab experiments, one pot and two greenhouse experiments, the suitability of the nitrate-online-measurement-system (NITROM) for the determination of nitrate concentration in soil solution was tested, calibrated and validated on a total of twelve soil types, two gardening substrates and three different cultures. For the calculation of the nitrate concentration from spectral data, simple and multiple linear regressions (SLR, MLR), as well as polynomial multiple regression (PMR), were compared. Lab results of the nitrate UV absorption between 230 and 260 nm in pure nitrate standards (0 – 1000 mg NO3-- L-1) showed highly linear relationships for several wavelengths (231 und 240 nm: R2 > 0.999, p < 0.001). Low nitrate concentrations (0 – 150 mg L-1) were precisely determined between 230 and 240 nm, while high nitrate concentrations (150 – 1000 mg L-1) were determined between 240 and 250 nm. For UV measurements in soil solution with several interfering substances, no linearity was achieved (see below). The predominant interfering substances for nitrate measurements in the field are aromatic and alkene compounds in dissolved organic carbon (DOC). The complex structure of DOC may only be considered in a calibration through a multi-wavelength approach, accounting for wavelengths from the ranges of high and low nitrate concentrations as well as the reference range without nitrate absorption (250 – 260 nm). The PMR, in comparison to SLR and MLR, fit best for the estimation of nitrate concentration from spectral data. This can be seen in the field data obtained from the first greenhouse experiment (PMR: R2 = 0.963, p < 0.001; MLR: R2 = 0.948, p < 0.001; SLR 232 nm: R2 = 0.093, p = 0.047). The pot experiment with three different soil types and two gardening substrates allowed i.a. conclusions of DOC quality on different sites and confirms the need for a site-specific calibration of the measurement method. During the second greenhouse experiment, the entire NITROM technology was tested. Data obtained during half an hour intervals over a period of five weeks was evaluated online. Using a PMR calibration, a soil nitrate content curve (n = 998) was created and fertilizer loads were adapted. The fertilization events are clearly recognizable as distinct peaks in the graph. The PMR calibration (with 15 wavelength and n = 36) was highly significant (p = 0.001) and had a R2 > 0.999. The validation of the calibration reveals a relative estimation error of 6.1 %. The suitability of this method for in-situ determination of the nitrate concentration, as well as an adapted and culture specific fertilization management on the basis of measured data, can be confirmed. Further improvements to refine the measurement technology and evaluation procedure, as well as calibration of the method for DOC, are planned.