Lake Naivasha is a freshwater lake in the East African Rift Valley, which was affected by a continuously declining water level between 1980 and 2011. The newly exposed littoral area has been gradually put under agricultural ...

Die Landwirtschaft ist über die Ausbringung von Dünger Hauptverursacher diffuser Nährstoffeinträge in deutsche Gewässer. Sie ist somit mitverantwortlich dafür, dass das erklärte Ziel eines „guten ökologischen Zustands“ ...

Rainfed lowland rice is the dominant food crop in the low-input agricultural systems of Cambodia. The main production area is characterized by sandy soils with low contents in nitrogen, phosphorus and organic matter, as well as low cation exchange capacity. The use efficiency of applied nutrients is reportedly very low, and the outcome of nutrient application strategies is highly variable. This study assesses the potential of organic manures to replace mineral N fertilizers in rainfed lowland rice-based production systems on sandy soils of Cambodia. It comprised field experiments and surveys. Four field experiments were conducted between 2013 and 2014 and differed by district and soil type (shallow vs. deep). Treatments compared the recommended rates of applied mineral N, with farmyard manure and mungbean (Vigna radiate) used as a pre-rice leguminous green manure. Legume treatments were further varied including with or without P application to the green manure and different residue management strategies (all residues returned, only grain harvested, all residues removed). The survey investigated farmers’ perceptions regarding potentials and constraints to leguminous green manure adoption (here mungbean). The analysis of all manure-amended plots (farmyard and green manure combined) showed that organic manure could replace approximately 50% of the mineral N recommended for sandy soils. In addition, the use of organic amendments entailed significant increases in residual soil C and N after only one cropping cycle, suggesting that soil fertility may be enhanced in the long-term. In the case of mungbean green manure, the N₂ fixation measured by the δ¹⁵N natural abundance varied from 9 to 78 kg N ha^-1 (average of 36 kg N ha^-1). Highest N₂ fixation was associated with low rainfall intensity during legume establishment and the absence of soil flooding during the pre-rice period. Only on deep sandy soils, the addition of 10 kg P ha^-1 to mungbean was able to more than double the amount of N₂ fixation compared to the legume without P amendment. The incorporation of P-amended legume residues (total biomass or after grain harvest) produced in both soil types rice grain yields that were comparable those obtained with the recommended mineral N application rate. Similarly, farmyard manure applied at 60 kg N ha^-1 produced a rice yield comparable to mineral fertilizer N, however only in the deep soils. The study of farmers’ perception and adoption of organic amendments highlights that the use of farmyard manure is widespread but that its efficiency to replace mineral N is highly soil-specific. However, the availability of farmyard manure will be increasingly constrained by declining cattle numbers. While the adoption of legume green manures is potentially high, their actual use is constrained by soil P availability and limited to sites without soil flooding during the pre-rice niche and to systems with sufficient labor availability of biomass incorporation. While organic amendments have the potential to replace mineral fertilizers, such options and use strategies are highly site- and system specific....
<strong>Potenzial organischer Dünger in Reisanbausystemen auf sandigen Böden im Tiefland von Kambodscha</strong><br /> Regengespeister Nass-Reis ist das vorherrschende angebaute Nahrungsmittel in extensiven Agrarsystemen von Kambodscha. Die überwiegenden Teile des Anbaugebiets sind durch sandige Böden mit geringen Gehalten an Stickstoffgehalt, Phosphor, und organischer Substanz sowie niedriger Kationenaustauschkapazität geprägt. Auch die Nutzungseffizienz extern über mineralische oder organische Düngung zugeführter Nährstoffe ist in der Regel sehr gering und oft extrem variabel. Die vorliegende Studie untersucht das Potenzial der Anwendung organischer Dünger zu Nass-Reis im Regenfeldbau auf sandigen Böden in Kambodscha im Hinblick auf den Ersatz der kaum verfügbaren mineralischen N Dünger. Vier Feldexperimente wurden zwischen 2013 und 2014 durchgeführt. Sie unterschieden sich durch die Lage (Bezirk und Bodentyp – flachgründig vs. tiefgründig), die empfohlene Rate von mineralischem N und die Integrationen von Leguminosen in das Anbausystem (P-Anwendung zu Reis oder der Leguminose, Rückführung der Ernterückstände). Ferner wurde die Akzeptanz, Einschränkung und die Wahrnehmung von Bauern gegenüber Leguminosen als Gründünger im Vergleich zu Stallmist und Mineraldünger untersucht.<br /> Die organische Düngung vermochte im Mittel etwa 50% der empfohlene Mineral-N-Dünger-gabe für sandige Böden zu ersetzen und gleichzeitig die Gehalte der Böden an organischem C und N bereits nach einem Anbauzyklus signifikant zu erhöhen, was eine Verbesserung der Bodenfruchtbarkeit bei längerfristigen Anwendung vermuten lässt. Im Falle von Gründünger (hier Mungbohne) variierte die N₂-Bindung, die mit Hilfe der natürlichen Abundanz-Methode (δ¹⁵N’) gemessen wurde, zwischen 9 und 78 kg N ha^-1 (durchschnittlich 36 kg N ha^-1). Hohe Werte der N₂-Bindung durch die Leguminosen waren mit geringem Niederschlag während der Vorfruchtperiode assoziiert, was darauf hinweist, dass die N₂-Bindung von der Bodenhydrologie (hier temporärer Wasserüberstau) beeinfluss wird. Auf tiefgründigen Böden führte die Zugabe von 10 kg P ha^-1 zu Mungbohne zu einer Verdoppelung der N₂-Bindung verglichen zum Anbau ohne P- Zufuhr. Die Einarbeitung von Ernterückständen der Mungbohne erzielte in beiden Bodentypen vergleichbare Reiserträge wie bei empfohlener mineralischer N-Zufuhr. Eine Stallmistgabe, äquivalent zu 60 kg N ha^-1, erzielte ebenfalls einen Reisertrag vergleichbar dem einer empfohlenen Mineral-N-Düngung auf tiefgründigen, jedoch nicht auf flachgründigen Böden.<br /> Die Akzeptanzstudie vermochte zu zeigen, dass die Nutzung von Stallmist in der Region weit verbreitet ist und mineralischen Dünger in Abhängigkeit des Bodentyps effizient zu ersetzen vermag. Allerdings ist die Verfügbarkeit von Mist durch sinkende Viehbestände in der Region zunehmend limitiert. Die Akzeptanz von Leguminosen zur Gründüngung im Regenfeld-Reisanbau ist potentiell hoch, allerdings unter den Voraussetzungen, dass hinreichend verfügbares P vorhanden ist, dass die Flächen während der Zwischenfrucht- Anbauperiode nicht überflutet sind, und dass Arbeitskräfte für die Einarbeitung der Biomasse zur Verfügung stehen. Ich kann gefolgert werden, dass Lösungsansätze und Technologie-Optionen zur organischen Düngung Standort- und System-spezifisch erfolgen müssen....

The aim of this work was to test strategies, which improve nutrient supply and weed control in occasional direct-seeded (DS) grain legumes in Organic Agriculture. The effect of intra-row fertilisation of rock phosphate (RP) and several sulphur fertilisers on crop growth, yield and nutrient uptake was studied in field trials with faba bean (Vicia faba) in Germany (two sites in NRW, 2011 and 2012) and with soybean (Glycine max) in Brazil (three sites in Paraná, 2012 and 2013). The second part of this work investigated weed control with natural herbicides (NH). Therefore, eighteen screening trials in the field and five field trials with soybean and common bean (Phaseolus vulgaris) were conducted in Brazil. Additionally, the effect of different amounts of oats straw residue on faba bean and weed shoot growth were examined as a second trial factor within the 2012 fertiliser trials in Germany. <br /> Soils at all <u>fertiliser trials</u> in Germany exhibited sufficient P-contents (LUFA C) and the intra-row<br /> fertilisation of RP (50 kg/ha^-1 P) did not have any effect on faba bean growth and P-uptake, neither alone nor in combination with elemental sulphur, which by way of in situ acid formation can enhance RP solubility. On the contrary, the sulphur fertilisers potassium sulphate, gypsum and elemental sulphur did result in a markedly increased S-uptake in both trial years, while faba bean growth and yield were only affected positively and in part significantly in the second trial year. The clear effect was assumed to be due to low soil sulphate contents during initial crop development, caused by low sulphate adsorption and hence high leaching rates during winter and also due to low soil organic matter (SOM) mineralisation rates under DS management. However in Brazil, soybean did not react to S-fertilisation with increased crop growth, yield or S-uptake in any trial. The sufficient S-supply was explained with the high contents of adsorbed sulphate in soil and high SOM mineralisation rates under tropical climate. P-fertiliser application was also ineffective at most sites due to sufficient to high soil P-contents. Only on a field with low P-contents at site Ponta Grossa P-fertilisation had a positive effect on P-uptake, crop growth and yield. In both years this positive effect was increased by simultaneous application of elemental sulphur, which presumably increased solubility of RP. <br /> In screening trials with <u>natural herbicides</u> pine oil and acidic acid were found to be the most potent active ingredients with a cell membrane disrupting (CMD) effect. While the sole spray application of high amounts of NaCl resulted in relatively weak plant damage, it was found that the combination of CMD and NaCl resulted in a strongly enhanced weed control. Additionally, a meristem damaging systemic effect of NaCl was identified, which was particularly strong for dicot weed species. In consequence, CMD amounts and hence application costs could be reduced drastically. Furthermore, it was determined repeatedly that emulsifiers influence formulation efficacy strongly at the rates commonly applied in NH and therefore these inert ingredients have to be considered as active ones in NH formulations. In the DS soybean field trial in Londrina it was determined that at a fixed total amount of AI (90 L/ha^-1 pine oil or limonene and 90 kg/ha^-1 NaCl) two concentrated applications resulted in a higher weed control than the three diluted ones. Weed control in this trial was not satisfactory, though, and crop growth as well as yield were markedly reduced compared to the clean control treatment. In the DS soybean trial<br /> in Ponta Grossa 50 L ha^-1 pine oil or limonene and 50 kg/ha^-1 NaCl were applied once, twice and three times. Even after three applications weed drymass remained relatively high compared to the weedy control. Nevertheless, soybean shoot drymass was not affected strongly by weed infestation and with three applications grain yield was close to the clean control. Nevertheless, results in this trial were influenced by crop damage due to contact with NH spray, because no working protective screen was available during application. In two field trials with conventionally tilled common bean, weed control was satisfactory in all spray treatments. Crop growth and yield were comparable to those of the weed free control....