Effect of nitrogen fertilizer rate and timing on sorghum productivity in Ethiopian highland Vertisols

Sorghum is cultivated on Vertisols in the Ethiopian Highlands. An experiment was conducted in the Gumara-Maksegnit watershed in 2013 and 2014 to assess the effect of rate and timing of nitrogen fertilizer application on the possibility to shorten the maturity period and to improve the productivity of sorghum. The experiment was laid out as Randomized Complete Block Design with three replications. Treatments were nitrogen doses between 0 and 87 kg N ha^?1 as urea applied at planting, at knee-height stage or in split doses at both stages. Results showed that application of 23, 41, 64 and 87 kg ha^?1 N gave a yield increase of 40, 53, 62 and 69% over the control (0 kg N ha^?1), respectively. In addition, split application of 41 kg ha^?1, 64 kg ha^?1 and 87 kg ha^?1 of nitrogen fertilizer, half at planting and half at knee height stage, gave 19%, 15% and 18% increase in sorghum grain yield over a single dose application, respectively. Applying 87 kg ha^?1 nitrogen fertilizer with split application half at planting and half at knee height stage, along with 46 kg ha^?1 of P₂O_5, gave the highest grain yield and income.     

Fuzzy modelling and mapping soil moisture for observed periods and climate scenarios. An alternative for dynamic modelling at the national and regional scale?

Key message

Average soil moisture was spatially modelled for observed periods and climate scenarios using a fuzzy logic approach. Accordingly, a significant decline of soil moisture until 2070 in Germany and the Kellerwald National Park could be evidenced for soils influenced by ground water and by stagnant water and at sites on steep slopes and on southerly slopes.

Context

Soil moisture is an essential environmental factor affecting the condition of forests throughout time with high spatial variance. To adapt forests to climate change, assessments of ecological integrity and services in forest management and nature conservation need spatio-temporal estimations of current and future soil moisture. Dynamic modelling of soil moisture even with rather simple models needs numerous data which are often not available for areas of large spatial extent.

Aims

Therefore, the objectives of this investigation were to (1) spatio-temporally estimate ecological soil moisture with available data covering the whole territory of Germany, (2) to specify these estimates for the regional scale, (3) to statistically analyse temporal trends of modelled soil moisture for the time period 1961–2070 and (4) to map soil moisture changes (drying-out) at both national and regional levels.

Methods

A fuzzy rule-based model was developed allowing the combination of a pedological and an ecological soil moisture classification. The fuzzy modelling approach was applied for mapping average soil moisture at two spatial scales.

Results

Soil moisture was modelled and mapped on a scale of 1:500,000 across Germany and regionally specified on a scale of 1:25,000 for the Kellerwald National Park for the time intervals 1961–1990, 1991–2010, 2011–2040 and 2041–2070. The model validation gave a root mean squared error (RMSE) of 0.86 and a coefficient of determination (pseudo R ²) of 0.21. Average soil moisture was expected to decline significantly until 2070 concerning soils influenced by ground water and by stagnant water and at sites on steep slopes (>?25%) and on southerly slopes (120–240°).

Conclusion

The model allows mapping of mean soil moisture at the national and regional scale as shown by the example of Germany and the Kellerwald National Park across observed periods and climate scenarios. It should be combined with available ecological data on forest ecosystem types (Jenssen et al. 2013; Schröder et al. 2015) and tested at the European scale.

     

Stimulation of methane oxidation by CH<Subscript>4</Subscript>-emitting rose chafer larvae in well-aerated grassland soil

In this study, the impact of rose chafer (Cetonia aurata L.) larvae on net and gross methane (CH₄) fluxes in soil from an old permanent grassland site (Giessen, Germany) was investigated. Previous studies at this site suggested the existence of Scarabaeidae larvae-induced “CH₄-emitting hot spots” within the soil profile which may subsequently lead to increased CH₄ oxidation. The net (soil + larvae) and gross (soil and larvae separated) CH₄ fluxes were studied in a 3-month laboratory incubation. Addition of larvae changed the soil from a net sink (?330 ± 11 ng CH₄ kg^?1 h^?1) to a net source (637 ± 205 ng CH₄ kg^?1 h^?1). Supply of plant litter to the soil + larvae incubation jars tended to increase CH₄ emissions which was not significant due to large variability. After 11–13 weeks of incubation, the net soil CH₄ oxidation was significantly stimulated by 13–21% in the treatments containing larvae when these were taken out. Analysis of archaeal 16S rRNA genes revealed that the majority of the obtained clones were closely related to uncultured methanogens from guts of insects and other animals. Other sequences were relative to cultivated species of Methanobrevibacter, Methanoculleus, and Methanosarcina. Hence, Scarabaeidae larvae in soils (i) may represent an underestimated source of CH₄ emissions in aerobic upland soils, (ii) may stimulate gross CH₄ consumption in their direct soil environment, and, thus, (iii) contribute to the spatial heterogeneity often observed in the field with closed-chamber measurements. Long-term CH₄-flux balances may be wrongly assessed when “exceptional” net CH₄ flux rates (due to larvae hot spots) are excluded from data sets.     

Rinsing of Saline Water from Road Salt in a Sandy Soil by Infiltrating Rainfall: Experiments,Simulations, and Implications

Saline melt water from road salt applications that has percolated into a fine sandy soil in winter is rinsed out of the soil by infiltrating rainwater in the following warmer seasons. This sequence of saturated and unsaturated flow processes associated with saline water transport in a fine sandy soil was studied by simulation and exploratory laboratory experiments. Experiments in soil columns of 300-μm sand revealed that two rinses of pure water, each of one pore volume, were sufficient to reduce the salt concentration by 99% of its original value in the soil column. Simulated time variations of salt concentration in the effluent from the column agreed with experimental results. Based on simulated and experimental results, a sandy soil must become saturated to experience pore water flow in order to efficiently rinse saline snowmelt water. Depending on the saturated hydraulic conductivity and the soil depth, days, weeks, or months of freshwater infiltration in summer are needed to rinse saline melt water from an unsaturated sandy soil after road salt applications in winter. This explains findings of significant salt concentrations in surface and shallow groundwater during summer months, long after road salt application and infiltration has ceased.     

Magnitude and Occurrence Probability of Soil Loss: A Risk Analytical Approach for the Plot Scale For Two Sites in Lower Austria

Long‐term contribution of soil loss events depends on both – the magnitude and the occurrence probability – but oftentimes, a limited observation period impedes the assessment of the temporal soil loss distribution. In this research, the event‐based soil loss from two plot locations in Lower Austria (Mistelbach and Pixendorf) was linked with the event‐based rainfall erosivity (EI₃₀) to assess the temporal soil loss distribution using long‐term rainfall data from two meteorological stations in Lower Austria. For both plot locations, a risk analysis was performed to (i) assess the long‐term average annual soil loss and to (ii) evaluate the contribution of incremental erosion events according to different event return periods. The risk analysis showed that in Pixendorf the events <20 years return period dominatingly contribute to long‐term soil loss, because the contribution of the events >20 years return period is progressively reduced through the low occurrence probability. On the contrary, in Mistelbach the soil loss magnitudes of the extreme events overcome the effect of the low occurrence probability, and consequently, the contribution of the extreme events (>20 years return period) is dominant. The spatially variable contribution of the erosion events reveals the need for spatially customized soil conservation strategies. A risk analytical approach may help to allocate the driving events and thus to define proper event design magnitudes for local soil conservation planning. Copyright © 2014 John Wiley & Sons, Ltd.