Cotton as an entry point for soil fertility maintenance and food crop productivity in savannah agroecosystems - Evidence from a long-term experiment in southern Mali
Ripoche, A. ; Crétenet, M. ; Corbeels, M. ; Affholder, F. ; Naudin, K. ; Sissoko, F. ; Douzet, J.M. ; Tittonell, P.A. - \ 2015
Field Crops Research 177 (2015). - ISSN 0378-4290 - p. 37 - 48.
organic-matter - nitrogen-fertilization - chemical-properties - nutrient dynamics - semiarid tropics - use efficiency - pearl-millet - burkina-faso - dry-matter - management
Given the scarcity of manure and the limited land available for fallowing, cotton cultivation with its input credit schemes is often the main entry point for nutrients in cropping systems of West Africa. In an experiment carried out during 25 years in southern Mali, the crop and soil responses to organic fertilizer (=OF), inorganic fertilizer (=IF), and a combination of both (=OIF) were quantified and compared to a control treatment for a typical cotton-sorghum-groundnut rotation. From 1965 to 1979 (15 years, period 1), fertilizers were only applied on cotton and the control treatment was not fertilized. From 1980 to 1989 (10 years, period 2), the amount of manure applied was split between cotton and sorghum, and inorganic fertilizers were applied to the three crops. Inorganic fertilizers were also applied to plots with cotton and sorghum that were previously unfertilized control treatments. In favorable rainfall seasons maximum yields of fertilized treatments reached ca. 3.5 t ha-1 in the case of cotton and groundnuts, and ca. 2 t ha-1 in the case of sorghum. During period 1, cotton yields were steady (ca. 1 t ha-1) when no fertilizers were added. Cotton yields were 20% higher in the OF and OIF treatments than in the IF treatment. Sorghum and groundnut benefited from residual effects of fertilizer application on cotton leading to a 200% and 50% yield increase respectively compared to the control treatment. During period 2, yields of the three crops were similar across fertilized treatments. Groundnut yields in the OF treatment, and cotton yields in the OF and IF treatments were respectively 45%, 30% and 20% significantly higher than those in the respective control treatments. No added benefit on crop yields was observed from the combined use of inorganic and organic fertilizer. Soil nutrient contents (SOC, N, P, K) did not significantly change in any of the treatments after 25 years. Soil pH decreased in treatments receiving inorganic fertilizer. Despite low level of soil organic matter, crops responded to organic or inorganic fertilization and crop productivity over time was mostly influenced by the interaction between fertilization and rainfall variability. Our results highlight the role of cotton in West African landscapes as an entry point of nutrients via fertilization, which impacts positively on the productivity of the other crops in the rotation. Credit schemes by the cotton company for farmers to purchase fertilizer to which they would otherwise not have access are thus crucial for sustained crop productivity.
Iron oxidation kinetics and phosphate immobilization along the flow-path from groundwater into surface water
Grift, B. van der; Rozemeijer, J.C. ; Griffioen, J. ; Velde, Y. van der - \ 2014
Hydrology and Earth System Sciences 18 (2014)11. - ISSN 1027-5606 - p. 4687 - 4702.
suspended sediment - ferrous iron - fresh-water - phosphorus limitation - nutrient dynamics - fe(ii) oxidation - arsenic removal - natural-waters - riparian zone - river
The retention of phosphorus in surface waters through co-precipitation of phosphate with Fe-oxyhydroxides during exfiltration of anaerobic Fe(II) rich groundwater is not well understood. We developed an experimental field set-up to study Fe(II) oxidation and P immobilization along the flow-path from groundwater into surface water in an agricultural experimental catchment of a small lowland river. We physically separated tube drain effluent from groundwater discharge before it entered a ditch in an agricultural field. Through continuous discharge measurements and weekly water quality sampling of groundwater, tube drain water, exfiltrated groundwater, and surface water, we investigated Fe(II) oxidation kinetics and P immobilization processes. The oxidation rate inferred from our field measurements closely agreed with the general rate law for abiotic oxidation of Fe(II) by O-2. Seasonal changes in climatic conditions affected the Fe(II) oxidation process. Lower pH and lower temperatures in winter (compared to summer) resulted in low Fe oxidation rates. After exfiltration to the surface water, it took a couple of days to more than a week before complete oxidation of Fe(II) is reached. In summer time, Fe oxidation rates were much higher. The Fe concentrations in the exfiltrated groundwater were low, indicating that dissolved Fe(II) is completely oxidized prior to inflow into a ditch. While the Fe oxidation rates reduce drastically from summer to winter, P concentrations remained high in the groundwater and an order of magnitude lower in the surface water throughout the year. This study shows very fast immobilization of dissolved P during the initial stage of the Fe(II) oxidation process which results in P-depleted water before Fe(II) is completely depleted. This cannot be explained by surface complexation of phosphate to freshly formed Fe-oxyhydroxides but indicates the formation of Fe(III)-phosphate precipitates. The formation of Fe(III)-phosphates at redox gradients seems an important geochemical mechanism in the transformation of dissolved phosphate to structural phosphate and, therefore, a major control on the P retention in natural waters that drain anaerobic aquifers.
Extending one-dimensional models for deep lakes to simulate the impact of submerged macrophytes on water quality
Sachse, R. ; Petzoldt, T. ; Blumstock, M. ; Moreira, S. ; Pätzig, M. ; Rücker, J. ; Janse, J.H. ; Mooij, W.M. ; Hilt, S. - \ 2014
Environmental Modelling & Software 61 (2014). - ISSN 1364-8152 - p. 410 - 423.
shallow eutrophic lakes - phytoplankton biomass - nutrient dynamics - phosphorus - ecosystem - growth - state - fish - zooplankton - vegetation
Submerged macrophytes can stabilise clear water conditions in shallow lakes. However, many existing models for deep lakes neglect their impact. Here, we tested the hypothesis that submerged macrophytes can affect the water clarity in deep lakes. A one-dimensional, vertically resolved macrophyte model was developed based on PCLake and coupled to SALMO-1D and GOTM hydrophysics and validated against field data. Validation showed good coherence in dynamic growth patterns and colonisation depths. In our simulations the presence of submerged macrophytes resulted in up to 50% less phytoplankton biomass in the shallowest simulated lake (11 m) and still 15% less phytoplankton was predicted in 100 m deep oligotrophic lakes. Nutrient loading, lake depth, and lake shape had a strong influence on macrophyte effects. Nutrient competition was found to be the strongest biological interaction. Despite a number of limitations, the derived dynamic lake model suggests significant effects of submerged macrophytes on deep lake water quality.
Crop resistance traits modify the effects of an aboveground herbivore, brown planthopper, on soil microbial biomass and nematode community via changes to plant performance.
Huang, J. ; Liu, M. ; Chen, F. ; Griffiths, B.S. ; Chen, X. ; Johnson, S.N. ; Hu, F. - \ 2012
Soil Biology and Biochemistry 49 (2012). - ISSN 0038-0717 - p. 157 - 166.
experimental grassland community - below-ground communities - animal trophic groups - nilaparvata-lugens - food-web - nutrient dynamics - carbon allocation - shoot herbivores - rice cultivars - root
Plant-mediated effects of aboveground herbivory on the belowground ecosystem are well documented, but less attention has been paid to agro-ecosystems and in particular how crop cultivars with different traits (i.e. resistance to pests) shape such interactions. A fully factorial experiment was conducted using four rice cultivars with different insect-resistance, with and without the aboveground herbivore Nilaparvata lugens (brown planthopper), and to test two hypotheses (1) aboveground herbivory affects the soil microbial biomass and nematode community by altering plant performance and soil resource availability and (2) herbivory effects will depend on cultivar resistance traits. Our results suggested that cultivar resistance mediated both herbivory intensity and herbivore effects on plant performance. N. lugens decreased the availability of soil resources (soluble sugars, amino acids, organic acids, dissolved organic carbon and nitrogen), microbial biomass and percentages of bacterivores when feeding on a susceptible cultivar but increased them in a resistant cultivar. However, total nematode abundance and the percentage of plant-parasitic nematodes responded in the opposite way, increasing under a susceptible cultivar and decreasing under a resistant cultivar. The development of plant-parasites under resistant cultivars before aboveground herbivory might contribute to their resistance traits. Our findings provide evidence that N. lugens significantly reversed the pattern of soil resource availability, microbial biomass and nematode community structure (abundance and trophic composition) across cultivars with distinct resistance. In the presence of aboveground pests, the agronomic use of resistant rice cultivars could also control populations of plant-parasites and promote soil resource availability, further extended to higher trophic level of soil food web.
Effects of litters with different concentrations of phenolics on the competition between Calluna vulgaris and Deschampsia flexuosa
Hofland-Zijlstra, J.D. ; Berendse, F. - \ 2010
Plant and Soil 327 (2010)1-2. - ISSN 0032-079X - p. 131 - 141.
caerulea l moench - mycorrhizal fungi - microbial activity - nutrient dynamics - alaskan taiga - l trin - l hull - nitrogen - soil - plant
We hypothesized that the outcome of competition between ericaceous plants and grasses is strongly affected by the concentrations of phenolics in the litter that they produce. To test the effect of phenolic-rich litter on soluble soil nitrogen concentrations, plant nitrogen uptake and inter-specific competition, we conducted a greenhouse experiment with the shrub Calluna vulgaris and the grass Deschampsia flexuosa and their leaf litters. Two litters of C. vulgaris were used, with equal nitrogen concentration but different (high and low) concentrations of total phenolics. The D. flexuosa leaf litter contained lower concentrations of phenolics, but higher concentrations of nitrogen than the C. vulgaris litters. The plants were grown in monocultures and in mixed cultures. Inorganic and dissolved organic nitrogen were measured monthly during the experiment. After four months, we measured above- and belowground biomass and the nutrient concentrations in above- and belowground plant parts. In monocultures, C. vulgaris produced more shoot and root biomass on its own litter than with no litter. Growth of Calluna was reduced on grass litter. D. flexuosa plants produced most biomass on their own litter type, whether in monocultures or in mixed cultures. Addition of Calluna litter stimulated the growth of D. flexuosa both in monoculture and in mixtures. The grass plants outcompeted Calluna both on shrub litter and on grass litter but not when grown without litter. The two C. vulgaris litter types that differed in their concentration of phenolics did not differ in their effects on the competition between the two species or on the production of inorganic and dissolved organic nitrogen. We conclude that the nitrogen content of the litter is more important as a plant feature driving competition between shrubs and grasses than the concentrations of phenolics
Can differences in soil community composition after peat meadow restoration lead to different decomposition and mineralization rates?
Dijk, J. van; Didden, W.A.M. ; Kuenen, F. ; Bodegom, P.M. van; Verhoef, H.A. ; Aerts, R. - \ 2009
Soil Biology and Biochemistry 41 (2009)8. - ISSN 0038-0717 - p. 1717 - 1725.
fresh-water wetlands - scots pine forest - nitrogen mineralization - microbial communities - northern wetlands - nutrient dynamics - food webs - carbon - diversity - protozoa
Reducing decomposition and mineralization of organic matter by increasing groundwater levels is a common approach to reduce plant nutrient availability in many peat meadow restoration projects. The soil community is the main driver of these processes, but how community composition is affected by peat meadow restoration is largely unknown. Furthermore, it is unclear whether restoration induced changes could lead to altered decomposition and mineralization rates. We determined soil community composition in restored peat meadows with different groundwater levels and soil pH. This composition was subsequently used in food web model calculations of C and N mineralization rates to assess whether differences in soil community composition may have contributed to differences in decomposition and mineralization rates observed between these meadows. Community composition of micro-organisms, Collembola and Enchytraeidae differed considerably between meadows and were correlated with differences in groundwater levels and soil pH. Collembolan and enchytraeid species from wet and neutral environments were more abundant at meadows with higher groundwater levels. Lower fungal to bacterial PLFA ratios and higher numbers of protozoa indicated an increased importance of the bacterial part of the food web at meadows with higher groundwater levels. Food web model calculations suggested that the observed changes in community composition would lead to higher rates of C and N mineralization at meadows with high groundwater levels. Results from modeling were consistent with field measurements of C mineralization, but not with measurements of N mineralization
Do competition and selective herbivory cause replacement of Phragmites australis by tall forbs?
Lenssen, J.P.M. ; Menting, F.B.J. ; Putten, W.H. van der - \ 2004
Aquatic Botany 78 (2004)3. - ISSN 0304-3770 - p. 217 - 232.
marsh plant zonation - salt-marsh - population-dynamics - community structure - nutrient dynamics - diverse habitats - insect herbivore - field experiment - shoot density - clonal plant
We investigated the role of biotic factors in determining abundance of the low marsh species Phragmites australis and the high marsh species Epilobium hirsutum. In a 2-year field experiment, at a position where Phragmites and Epilobium co-occurred, responses of both species to each other's removal were measured. In the second year, we also tested if larvae of Archanara geminipuncta, which feed exclusively on Phragmites shoots, affect the competitive ability of Phragmites relative to Epilobium. For both species, removal of aboveground material by clipping did not enhance shoot size or decrease variability in shoot size of the removed species itself. Surprisingly however, shoot numbers of both species increased after removal of the other, which demonstrates that there was a mutual inhibition of each other's abundance. Comparing the responses of Archanara-infested and non-infested Phragmites shoots revealed no increased competitive suppression by Epilobium due to selective herbivory. Instead, we found that herbivore activity was lower in plots with Epilobium, which demonstrates that Archanara population size is reduced by the presence of non-host plant species. These results contradict the common assumption that biotic factors constrain a species upper limit along flooding gradients. Instead, our result suggest that different biotic interactions may counteract each other and thus slow down replacement by successive species. (C) 2003 Elsevier B.V. All rights reserved.