Interaction of compost additives with phosphate solubilizing rhizobacteria improved maize production and soil biochemical properties under dryland agriculture

Dry land soils from the Indo-Gangetic plains are inherently poor in organic matter content and phosphorus (P). Amendment of these soils with P-enriched compost, together with P solubilizing rhizobacterial (PSR) inoculation has been suggested to improve plant growth and P uptake. We performed 3 x 2 factorial experiment using compost i.e. control, raw saw dust P compost (RPC) and acidified saw dust P compost (APC), and PSR inoculation as factors. The pot study investigated the effects of compost and PSR on maize growth, yield, P nutrition and soil biochemical properties. PSR inoculation with APC enhanced shoot length, cob diameter, grain yield and plant P uptake compared to control. APC amendment, either alone or in combination with PSR, also improved root growth and caused extension of rhizosphere by increasing the root length density of the maize plants. Significant improvement in soil biochemical properties i.e. dehydrogenase (DHA), beta-glucosidase (BGA), urease (UA) activity, dissolved organic carbon (DOC), soil organic carbon (SOC) and microbial biomass carbon (MBC) are due to the additive effect of compost amendments. A substantial increase in P availability and associated biochemical attributes reflect the significance of substrate quality, structural stability and optimized pH conditions of added compost that may have enhanced PSR performance, specifically with APC. Moreover, increased carboxylate secretions and PSR abundance in the root zone, lowering of pH and increase in rhizosphere fungal parameters, suggest PSR and APC to be synergetic driving of increased P availability for maize. We conclude that efficiency of P enriched compost could be increased with suitable compost additive in the presence of PSR in dry land soil.

Associative interplay of plant growth promoting rhizobacteria (Pseudomonas aeruginosa QS40) with nitrogen fertilizers improves sunflower (Helianthus annuus L.) productivity and fertility of aridisol

Muhammad Saleem Arif, Luca Bragazza, Alexandre Buttler, Vincent Eric Jules Jassey, Muhammad Riaz

The environmental and economic impacts of chemical fertilizer have encouraged farmers to integrate them with organic materials, an important nutrient management strategy for sustainable agriculture production. In the present study, we conducted field experiments to study the effects of nitrogen enriched compost (NEC) and mineral nitrogen (MN) fertilizer with a selected plant growth promoting rhizobacterial (PGPR) strain, Pseudomonas aeruginosa QS40, on productivity of sunflower and soil fertility. The results demonstrated that integrated application of PGPR with organic-inorganic N significantly increased shoot and root length, leaf area, total chlorophyll, head diameter, fresh biomass, straw-achene yield and N uptake in sunflower compared to unamended control and PGPR alone. The results also showed that integrated N biofertilizer regime enhanced soil microbial biomass, enzymatic activities and soil nitrogen contents. We also observed significant changes in rhizosphere soil pH, abundance of cultivable bacteria and arbuscular mycorrhizae fungi (AMF) root colonization. Treatment and year interaction was significant for dissolved organic carbon (DOC) and microbial biomass carbon (MBC) only. These results suggest that the efficiency of PGPR could be improved with increased availability of labile C substrate resource in NEC amended aridisol. We conclude that the application of NEC fertilizer with efficient PGPR biofertilizer may improve sunflower productivity and soil chemical and biological fertility in nutrient-poor agroecosystems of arid and semi-arid regions. (C) 2016 Elsevier B.V. All rights reserved.

Elsevier Science Bv2016

Regional and local scale pesticide transport in the alluvial plain of the Swiss Rhône River Valley

Kirsten Meiwirth

The herbicide transport and the groundwater vulnerability to pesticide contamination were studied in the alluvial aquifer of the Rhône River Valley near Martigny (Southwest Switzerland). The low clay and organic matter content of the soil, the intensive agricultural use, and the low depth of the groundwater table, lead to an alleged high vulnerability of the groundwater to contamination. Groundwater is used for irrigation, drinking water supply, and industrial purposes; it is of great economic and ecological importance which makes it particularly interesting to study. The work consists of local scale transport experiments and a regional monitoring of the groundwater over a two year period. At the local scale, two herbicides (atrazine and isoproturon) and a tracer were applied to instrumented field plots (4 m2) in two consecutive years and the transport through the vadose zone was studied in detail. Water flow and solute transport are closely linked to climatic factors. After the application, the pesticides remain at the soil surface as long as no precipitation occurs. Following to the first heavy rainfall, the chemicals are quickly transported through the vadose zone and part of them reaches the groundwater in a short time. During dry periods, the concentrations decrease steadily in the soil profile and the groundwater. After further rainfall, additional concentration peaks are observed in the groundwater, while only small peaks appear near the soil surface. Approximately 2.5 months after the application, the chemical concentration in the soil and in the groundwater has decreased considerably. The experimental results have been used to evaluate a mechanistic deterministic root zone model (HYDRUS-1D). The aim of the simulations was to define the processes involved in pesticide transport and, if possible, to predict the fate of chemicals applied at the soil surface. The MIM (mobile-immobile water) concept was used in order to account for the rapidity of the observed transport. In the study area, the shallow groundwater influences considerably the water conditions in the unsaturated zone; apparently, in such cases the use of a one-dimensional model to simulate the water flow and the chemical transport in the vadose zone is hindered due to difficulties in defining the lower boundary condition. Groundwater flow is typically three-dimensional and therefore, a global (saturated - unsaturated) 3-D model or the coupling of an unsaturated 1-D model to a 3-D saturated model would be more appropriate. Nevertheless, HYDRUS-1D allowed to describe qualitatively the observed results and to confirm the assumption that accelerated flow occurs on the experimental plots. At the regional scale, 13 piezometers were installed in an observation area (400 ha), and the groundwater was regularly analysed for the concentration of 6 herbicides (atrazine, terbutylazine, simazine, deethylatrazine, isoproturon, and diuron). Herbicides were detected in 12 piezometers, sometimes at high concentrations, but during a short period of time (mid May to mid July). Throughout the rest of the year, the concentrations remained below the drinking water limit. The observations are in good agreement with the conclusions of the local experiments (rapid transport, important influence of the climatic conditions, quick decrease of concentration peaks). Furthermore, the groundwater characteristics play an important role for the observation of herbicides. Near the Rhône river, high hydraulic gradients quickly dilute chemicals leaching from the fields above and herbicides coming from more distant fields may also be observed. Near the slope, an inflow of contaminated water from the hill side (vineyards) contributes to the groundwater contamination. Within the plain, high concentrations of herbicides applied to an above located field can temporarily be observed. Contaminations are confined in time and space and different substances are detected from one piezometer to another. This lack of continuity in pesticide concentrations will complicate the prediction of the solutes' fate in the groundwater, and a very precise knowledge of the pesticides use, both in space and time, is required.

EPFL2003

Riparian wetland properties counter the effect of land-use change on soil carbon stocks after rainforest conversion to plantations

Thomas Guillaume

Progressive conversion of tropical rainforests to agricultural monocultures in South East Asia increasingly affects landscape types such as riparian areas. The impacts of conversions on soil organic matter (SOM) vary with changing landforms. However, this was often not accounted for in previous studies where SOM in soils in riparian areas was combined with SOM from well-drained adjacent slopes. Because riparian areas have a high carbon (C) storage potential, our objectives were i) to assess their C stocks after conversion to rubber and oil palm plantations in Sumatra (Indonesia) and ii) to compare the impacts of land use conversion on C stocks between riparian and well-drained areas. Average soil C stock losses from the top 30 cm were about 14% and 4% following conversion of riparian forest to rubber and oil palm plantations, respectively, indicating a high resistance of C to mineralization. C losses from well-drained areas were twice as high as from riparian areas after the respective conversion. delta C-13 values from riparian areas showed clear heterogeneity down soil profiles that was explained i) by alternating oxic and anoxic conditions, leading to reduced SOM and litter decomposition in riparian areas and ii) by mineral sediments and organic matter deposition and accumulation by erosion from adjacent slopes covered by plantations. We conclude that riparian areas are more resilient in terms of soil C storage towards land-use change than well-drained areas because of sediment deposition and reduced oxygen availability. On this basis, we developed a conceptual model of the effects of land-use change and various ecotone characteristics on SOM mineralization in the top- and subsoil of riparian areas.

2021

Regional and local scale pesticide transport in the alluvial plain of the Swiss Rhône River Valley

Kirsten Meiwirth

EPFL2003