Soil, water and nutrient loss under conventional and organic vegetable production managed in small farms

Agricultural systems with conventional tillage and intensive use of agrochemicals, especially those on high slopes and with shallow soils, have the potential to release pollutants. This study aimed at evaluating the soil, water and nutrient lost via agricultural runoff in large plots (small catchments) under conventional and organic farming of vegetables as well as under forest (control) system in a Cambisol in the Campestre catchment. Samples of runoff were collected biweekly for one year through a Coshocton wheel. The soil and water losses from the conventional farming were 218 and 6 times higher, respectively, than forest. Under organic farming the soil and water losses were 12 and 4 times higher, respectively, than forest. However the soil losses (0.5 to 114 kg ha^(−1) year^(−1)) are considered low in agronomy but environmentally represent a potential source of surface water contamination by runoff associated pollutants. The concentrations and losses of all forms of phosphorus (P) were higher in the conventional system (9.5, 0.9 and 0.3 mg L^(−1) of total P for conventional, organic and forest systems, respectively), while the organic system had the highest concentrations and losses of soluble nitrogen (4.7, 38.6 and 0.4 mg L^(−1) of NO_3-N, respectively). The percentage of bioavailable P was proportionally higher in the organic system (91% of total P lost was as bioavailable P), indicating greater potential for pollution in the short term.

Downscaling and Modeling the Effects of Climate Change on Hydrology and Water Resources in the Upper Blue Nile River Basin, Ethiopia

The Upper Blue Nile River Basin (UBNRB) located in the western part of Ethiopia, between 7° 45’ and 12° 45’N and 34° 05’ and 39° 45’E has a total area of 174962 km2 . More than 80% of the population in the basin is engaged in agricultural activities. Because of the particularly dry climate in the basin, likewise to most other regions of Ethiopia, the agricultural productivity depends to a very large extent on the occurrence of the seasonal rains. This situation makes agriculture highly vulnerable to the impact of potential climate hazards which are about to inflict Africa as a whole and Ethiopia in particular. To analyze these possible impacts of future climate change on the water resources in the UBNRB, in the first part of the thesis climate projection for precipitation, minimum and maximum temperatures in the basin, using downscaled predictors from three GCMs (ECHAM5, GFDL21 and CSIRO-MK3) under SRES scenarios A1B and A2 have been carried out. The two statistical downscaling models used are SDSM and LARS-WG, whereby SDSM is used to downscale ECHAM5-predictors alone and LARS-WG is applied in both mono-model mode with predictors from ECHAM5 and in multi-model mode with combined predictors from ECHAM5, GFDL21 and CSIRO-MK3. For the calibration/validation of the downscaled models, observed as well as NCEP climate data in the 1970 - 2000 reference period is used. The future projections are made for two time periods; 2046-2065 (2050s) and 2081-2100 (2090s). For the 2050s future time period the downscaled climate predictions indicate rise of 0.6°C to 2.7°C for the seasonal maximum temperatures Tmax, and of 0.5°C to 2.44°C for the minimum temperatures Tmin. Similarly, during the 2090s the seasonal Tmax increases by 0.9°C to 4.63°C and Tmin by 1°C to 4.6°C, whereby these increases are generally higher for the A2 than for the A1B scenario. For most sub-basins of the UBNRB, the predicted changes of Tmin are larger than those of Tmax. Meanwhile, for the precipitation, both downscaling tools predict large changes which, depending on the GCM employed, are such that the spring and summer seasons will be experiencing decreases between -36% to 1% and the autumn and winter seasons an increase of -8% to 126% for the two future time periods, regardless of the SRES scenario used. In the second part of the thesis the semi-distributed, physically based hydrologic model, SWAT (Soil Water Assessment Tool), is used to evaluate the impacts of the above-predicted future climate change on the hydrology and water resources of the UBNRB. Hereby the downscaled future predictors are used as input in the SWAT model to predict streamflow of the Upper Blue Nile as well as other relevant water resources parameter in the basin. Calibration and validation of the streamflow model is done again on 1970-2000 measured discharge at the outlet gage station Eldiem, whereby the most sensitive out the numerous “tuneable” calibration parameters in SWAT have been selected by means of a sophisticated sensitivity analysis. Consequently, a good calibration/validation model performance with a high NSE-coefficient of 0.89 is obtained. The results of the future simulations of streamflow in the basin, using both SDSM- and LARS-WG downscaled output in SWAT reveal a decline of -10% to -61% of the future Blue Nile streamflow, And, expectedly, these obviously adverse effects on the future UBNRB-water availibiliy are more exacerbated for the 2090’s than for the 2050’s, regardless of the SRES.

Aspekte des Prozesses der N-Freisetzung aus Humus-Vorratsabbau

In der vorliegenden Arbeit werden die Auswirkungen von Umweltveränderungen in einem N-gesättigten Buchenwaldökosystem über Basalt (Braunerde) untersucht. Unter veränderten Umweltbedingungen sind hier vor allem Bestandesdachauflösung, immissions- oder waldbaulich bedingt, und Klimaveränderung zu verstehen, die eine Erwärmung des Oberbodens zur Folge haben. Die Änderungen der Umweltbedingungen werden in diesem Versuchsansatz durch einen waldbaulichen Eingriff simuliert, durch den eine Bestandeslücke entsteht, die in einer Erwärmung des Bodens resultieren und damit den Wasser- und Elementhaushalt insgesamt beeinflussen. Es wird deutlich, dass die in der vorliegenden Arbeit untersuchten Flächen als N-gesättigt bezeichnet werden können, da die N-Verluste aus dem System die Größe der Einträge überschreiten. In der Folge ist es zu einer Entkopplung des Stoffhaushalts und damit zu erhöhter N-Mobilisierung gekommen. Diese konnte vor allem im hydrologischen Jahr 1996 dokumentiert werden; der Überschuss-N-Output liegt auf der Auflichtungsfläche bei bis zu 50 kg N/(ha*a)! Die beobachteten hohen N-Austräge erfolgten trotz eines ebenfalls beobachteten Anwachsens des mikrobiellen Stickstoff-Pools und des Aufwachsens einer krautigen und strauchigen Vegetation auf der Auflichtungsfläche. Im Jahresgang konnten auf der Auflichtungsfläche in 0 - 30 cm Bodentiefe maximale Änderungen im Nmic-Vorrat von 130 kg N/(ha*a) beobachtet werden. Das im Frühjahr beginnende quantitative Anwachsen des mikrobiellen Stickstoff-Pools mit dem Jahresgang zeigt vor allem dessen Temperaturabhängigkeit auf. Die am Ende der Vegetationsperiode deutlich ansteigenden Austragsraten zeigen jedoch an, dass der freigesetzte Stickstoff auch von den Mikroorganismen nicht dauerhaft im System gehalten werden kann, da mit fallender Temperatur auch die Mikroorganismen absterben und der in ihrer Biomasse gespeicherte Stickstoff freigesetzt wird. Aufwachsende Vegetation auf der Auflichtungsfläche konnte einen Großteil des Netto-Stickstoff-Jahreseintrages aufnehmen. Da die "Netto-Jahres-Mineralisation" 1996 leicht über der Wurzelaufnahme liegt, verbleibt ein Rest, der nicht von der aufwachsenden krautigen Vegetation der Auflichtungsfläche aufgenommen werden kann. Ergebnis ist damit, dass die auf Lochhieben aufwachsende krautige und strauchige Vegetation eine temperaturbedingte Stickstoffmobilisierung nur teilweise kompensieren kann. Allein aufwachsende verholzende Vegetation kann Stickstoff langfristig im System binden.

Studies on arbuscular mycorrhiza (AM) in the Alentejo (Portugal) using pea mutants resistant to AM fungi as a control tool for field conditions

The utilization and management of arbuscular mycorrhiza (AM) symbiosis may improve production and sustainability of the cropping system. For this purpose, native AM fungi (AMF) were sought and tested for their efficiency to increase plant growth by enhanced P uptake and by alleviation of drought stress. Pot experiments with safflower (Carthamus tinctorius) and pea (Pisum sativum) in five soils (mostly sandy loamy Luvisols) and field experiments with peas were carried out during three years at four different sites. Host plants were grown in heated soils inoculated with AMF or the respective heat sterilized inoculum. In the case of peas, mutants resistant to AMF colonization were used as non-mycorrhizal controls. The mycorrhizal impact on yields and its components, transpiration, and P and N uptake was studied in several experiments, partly under varying P and N levels and water supply. Screening of native AMF by most probable number bioassays was not very meaningful. Soil monoliths were placed in the open to simulate field conditions. Inoculation with a native AMF mix improved grain yield, shoot and leaf growth variables as compared to control. Exposed to drought, higher soil water depletion of mycorrhizal plants resulted in a haying-off effect. The growth response to this inoculum could not be significantly reproduced in a subsequent open air pot experiment at two levels of irrigation and P fertilization, however, safflower grew better at higher P and water supply by multiples. The water use efficiency concerning biomass was improved by the AMF inoculum in the two experiments. Transpiration rates were not significantly affected by AM but as a tendency were higher in non-mycorrhizal safflower. A fundamental methodological problem in mycorrhiza field research is providing an appropriate (negative) control for the experimental factor arbuscular mycorrhiza. Soil sterilization or fungicide treatment have undesirable side effects in field and greenhouse settings. Furthermore, artificial rooting, temperature and light conditions in pot experiments may interfere with the interpretation of mycorrhiza effects. Therefore, the myc- pea mutant P2 was tested as a non-mycorrhizal control in a bioassay to evaluate AMF under field conditions in comparison to the symbiotic isogenetic wild type of var. FRISSON as a new integrative approach. However, mutant P2 is also of nod- phenotype and therefore unable to fix N2. A 3-factorial experiment was carried out in a climate chamber at high NPK fertilization to examine the two isolines under non-symbiotic and symbiotic conditions. P2 achieved the same (or higher) biomass as wild type both under good and poor water supply. However, inoculation with the AMF Glomus manihot did not improve plant growth. Differences of grain and straw yields in field trials were large (up to 80 per cent) between those isogenetic pea lines mainly due to higher P uptake under P and water limited conditions. The lacking N2 fixation in mutants was compensated for by high mineral N supply as indicated by the high N status of the pea mutant plants. This finding was corroborated by the results of a major field experiment at three sites with two levels of N fertilization. The higher N rate did not affect grain or straw yields of the non-fixing mutants. Very efficient AMF were detected in a Ferric Luvisol on pasture land as revealed by yield levels of the evaluation crop and by functional vital staining of highly colonized roots. Generally, levels of grain yield were low, at between 40 and 980 kg ha-1. An additional pot trial was carried out to elucidate the strong mycorrhizal effect in the Ferric Luvisol. A triplication of the plant equivalent field P fertilization was necessary to compensate for the mycorrhizal benefit which was with five times higher grain yield very similar to that found in the field experiment. However, the yield differences between the two isolines were not always plausible as the evaluation variable because they were also found in (small) field test trials with apparently sufficient P and N supply and in a soil of almost no AMF potential. This similarly occurred for pea lines of var. SPARKLE and its non-fixing mycorrhizal (E135) and non-symbiotic (R25) isomutants, which were tested in order to exclude experimentally undesirable benefits by N2 fixation. In contrast to var. FRISSON, SPARKLE was not a suitable variety for Mediterranean field conditions. This raises suspicion putative genetic defects other than symbiotic ones may be effective under field conditions, which would conflict with the concept of an appropriate control. It was concluded that AMF resistant plants may help to overcome fundamental problems of present research on arbuscular mycorrhiza, but may create new ones.

Field measurements of the CO2 evolution rate under different crops during an irrigation cycle in a mountain oasis of Oman

For millennia oasis agriculture has been the backbone of rural livelihood in the desertic Sultanate of Oman. However, little is known about the functioning of these oasis systems, in particular with respect to the C turnover. The objective was to determine the effects of crop, i.e. alfalfa, wheat and bare fallow on the CO2 evolution rate during an irrigation cycle in relation to changes in soil water content and soil temperature. The gravimetric soil water content decreased from initially 24% to approximately 16% within 7 days after irrigation. The mean CO2 evolution rates increased significantly in the order fallow (27.4 mg C m^−2 h^−1) < wheat (45.5 mg C m^−2 h^−1) < alfalfa (97.5 mg C m^−2 h^−1). It can be calculated from these data that the CO2 evolution rate of the alfalfa root system was nearly four times higher than the corresponding rate in the wheat root system. The decline in CO2 evolution rate, especially during the first 4 days after irrigation, was significantly related to the decline in the gravimetric water content, with r = 0.70. CO2 evolution rate and soil temperature at 5 cm depth were negatively correlated (r = -0.56,n = 261) due to increasing soil temperature with decreasing gravimetric water content.

Konstruktive und funktionale Entwicklung eines selbststeuernden Unterflurbewässerungsverfahrens

Unter Einfluss des gegenwärtigen Klimawandels sowie dem Anstieg der Erdbevölkerung ist der effiziente Umgang mit den vorhandenen Wasserressourcen ein zentrales Thema in der Bewässerungslandwirtschaft. Die Unterflurbewässerung ist ein seit Jahrtausenden bekanntes Verfahren, bei dem das Bewässerungswasser unterhalb der Erdoberfläche aufgebracht wird und der Pflanze direkt im Wurzelraum zur Verfügung steht. Die Gefäßbewässerung ist ein selbststeuerndes Verfahren wobei die Wassergabe aus dem unglasierten Tongefäß aufgrund der im umgebenden Boden anliegenden Saugspannung erfolgt. Diese wassersparende und dem Wasserbedarf der Pflanze angepasste Bewässerungsweise ist Grundlage der Überlegungen und Untersuchungen der vorliegenden Arbeit. Ausgehend von dem Gedanken der Kombination der Vorteile der Gefäßbewässerung mit denen moderner Materialien, die eine maschinelle Installation ermöglichen und eine lange Lebensdauer aufweisen, wurde die Entwicklung einer selbststeuernden Bewässerung verfolgt. Materialrecherchen und eine Auswahl als geeignet identifizierter Materialien führten zu Laboruntersuchungen an Hand derer die Darcy-Eigenschaften (linearer Zusammenhang zwischen Volumenstrom und anliegendem Druck) überprüft wurden. Membranen erwiesen sich danach als geeignet, so dass an einer ausgewählten Schlauchmembran weitergehende Untersuchungen zum Einsatz für die Bewässerung vorgenommen wurden. Diese umfassten Langzeitlaborversuche im Boden zur Untersuchung der Entwicklung der Durchlässigkeit der Schlauchmembran über die Zeit, sowie zum Nachweis der Selbststeuerung des Systems. Mit den gewonnenen Ergebnissen war es möglich großmaßstäbliche Versuche im Gewächshaus zu realisieren, bei der die Schlauchmembran im Vergleich zur Tropfbewässerung hinsichtlich Wasserverbrauch und Ernteertrag an Standorten in Deutschland und Algerien getestet wurde. Diese Gewächshausversuche zeigten vielversprechende Ergebnisse für die Membranschlauchbewässerung mit im Vergleich zur Tropfbewässerung erhöhten Erträgen bei gleichzeitig geringerem Wasserverbrauch. Dies wurde besonders bei Verwendung von Bewässerungswasser mit erhöhtem Salzgehalt deutlich. Sorgfältiger Beachtung bedarf die Wasserqualität, da die Membranschlauchbewässerung auf Wasserverunreinigungen mit Durchflussverminderung reagiert, die sich nachteilig auf die Pflanzenentwicklung auswirkt. Aufgabe weiterer Forschungen muss es demnach sein, technische Verfahren zu entwickeln, die die langfristige Leistungsfähigkeit der Membran im Bewässerungsbetrieb aufrechterhalten.