Nitrogen Budgets and Soil Nitrogen Stocks of Organic and Conventional Cropping Systems: Trade-Off between Efficiency and Sustainability of Nitrogen Use

Organic and conventional cropping systems differ in the nature and amounts of nitrogen (N) inputs, which may affect efficiency and sustainability of N use. In the DOK (bio-Dynamic, bio-Organic, Konventionell) field experiment, organic and conventional cropping systems have been compared since 1978 at two fertilization levels. Nitrogen inputs via manure and/or mineral fertilizers, and N exports from plots with harvested products have throughout been recorded. For all treatments, N outputs with harvests have exceeded the inputs with fertilizers. Over the past years, symbiotic N2 fixation by soybean and clover grown in the trial has additionally been assessed, indicating average annual inputs of about 100 kg ha-1 yr-1 of N fixed from the atmosphere. Soil surface budgets opposing N inputs via fertilization, symbiotic fixation, seeds and deposition to N outputs via harvested products have been computed at the plot level for the duration from 1985 to 2012. The resulting balances range from negative values of about -20 kg N ha-1 yr-1 (where outputs exceed the sum of said N inputs) to surpluses of about +50 kg N ha-1 yr-1. The budget based N use efficiency (NUE; N output via harvested products divided by sum of N inputs) in the case of negative balances suggests irrationally high NUE (>100%), while positive balances are related to lower NUE for treatments with inputs exceeding outputs. Negative balances, however, indicate soil N mining, while surpluses point to a risk of N losses, and/or N accumulation in the soil. Estimation of soil N stock changes based on yearly total N concentration measurements in the topsoil layer is currently ongoing. Preliminary results suggest that soil N stocks in the topsoil decreased under all treatments more than expected from the N balance, and that positive N balances are needed to maintain topsoil N stocks. An increase in soil N concentration was observed in none of the treatments. In conclusion, the results indicate an efficiency-sustainability trade-off. Treatments with a higher NUE lose more soil stock N than those with a lower NUE. Treatments with lower NUE indicate higher N losses from the studied crop-topsoil system. Sustainable soil N management in addition to organic fertilizer inputs might at this site require reduced soil tillage. The significance of N contained in deeper soil layers, and deep rooting crops in recovering leached N should as well be investigated

New insights in below ground nitrogen of clover-grass mixtures

Estimates of symbiotic nitrogen fixation (SNF) of clover in mixtures usually consider only aboveground clover nitrogen (N). However, belowground inputs of clover N derived from SNF via roots and rhizodeposition and its transfer to associated grass may contribute significantly to the amount of symbiotically fixed clover N. A microplot study with a red clover ( L.)-perennial ryegrass ( L.) model mixture was conducted within zero fertilised, bio-organic and conventional field plots of the DOK (bio-Dynamic, bio-Organic, Konventionell) long-term experiment during two consecutive years

Photon-bunching measurement after 2x25km of standard optical fibers

To show the feasibility of a long distance partial Bell-State measurement, a Hong-Ou-Mandel experiment with coherent photons is reported. Pairs of degenerate photons at telecom wavelength are created by parametric down conversion in a periodically poled lithium niobate waveguide. The photon pairs are separated in a beam-splitter and transmitted via two fibers of 25km. The wave-packets are relatively delayed and recombined on a second beam-splitter, forming a large Mach-Zehnder interferometer. Coincidence counts between the photons at the two output modes are registered. The main challenge consists in the trade-off between low count rates due to narrow filtering and length fluctuations of the 25km long arms during the measurement. For balanced paths a Hong-Ou-Mandel dip with a visibility of 47.3% is observed, which is close to the maximal theoretical value of 50% developed here. This proves the practicability of a long distance Bell state measurement with two independent sources, as e.g. required in an entanglement swapping configuration in the scale of tens of km.Comment: 6 pages, 5 figure

Phosphorus status and cycling in native savanna and improved pastures on an acid low-P Colombian Oxisol

On acid low-phosphorus (P) Colombian Oxisols, improved pastures with acid-soil-tolerant grass and legume varieties have increased beef production by a factor of 10 to 15 with only modest P fertilizer inputs. This indicates that the efficiency of P fertilization could be greater than is commonly expected on such strongly P-sorbing soils. To understand the effect of improved pastures on P cycling and availability, we estimated P budgets, and characterized soil P by sequential fractionation, isotopic exchange and biological activity measurements on soil samples from unfertilized native savanna, and fertilized improved grass-only (Brachiaria decumbens cv. Basilisk) and grass-legume (B. decumbens + Pueraria phaseoloides, Kudzu) pastures established in 1978 on a medium-textured isohyperthermic, tropeptic haplustox. Comparison of calculated P budgets, based on inputs and exports, with total soil P contents showed that fertilization, as part of the improved pasture management, had resulted in a measurable increase of total P in the surface 0-20 cm soil layer of nearly 30 mg kg-1 or about 20% over the savanna level. Sequential soil P fractionation of different seasonal samplings indicated that grass-legume maintained higher organic and available inorganic P levels with less temporal variation than the two other types. The linkage of organic P and available P was also reflected in soil biological activity. Estimates of P in microbial biomass and phosphatase activity were significantly higher in grass-legume than grass-only and savanna. The improvement in soil P availability, as measured by solution P concentration, P sorption and exchangeable P, was much greater in grass-legume than in grass-only. With comparable fertilizer inputs and greater product exports, improved P availability in grass-legume cannot be due to differences in budgets but can be attributed to changes in the overall biological activity in the soil-plant system caused by the presence of legumes in the vegetation cover. Total C, organic P content and macrofaunal activity were all significantly higher in grass-legume soils. Greater turnover of organic litter in grass-legume may provide for steadier organic P inputs and, therefore, higher P cycling and availabilit

Soil phosphorus (P) budgets, P availability and P use efficiencies in conventional and organic cropping systems of the DOK trial

Cropping systems rely on the provision of adequate amounts of phosphorus (P) to enable stable crop yields. A balanced application of P is necessary to avoid reduced crop yields (in case of too low application rates), but also to avoid P losses to other ecosystems (in case of too high application rates). While in conventional cropping systems the use of synthetic P fertilizers is common practice, organic cropping systems mostly rely on organic P inputs such as farmyard manure or compost. We aimed to answer if different cropping systems attain balanced P application rates in the long run, and how plant P availability is affected by different cropping systems and forms of fertilizers applied

Phosphorus Transformations in an Oxisol under contrasting land-use systems: The role of the soil microbial biomass

It is generally assumed that phosphorus (P) availability for plant growth on highly weathered and P-deficient tropical soils may depend more on biologically mediated organic P (Po) turnover processes than on the release of adsorbed inorganic P (Pi). However, experimental evidence showing the linkages between Po, microbial activity, P cycling and soil P availability is scarce. To test whether land-use systems with higher soil Po are characterized by greater soil biological activity and increased P mineralization, we analyzed the partitioning of P among various organic and inorganic P fractions in soils of contrasting agricultural land-use systems and related it to biological soil properties. Isotopic labeling was used to obtain information on the turnover of P held in the microbial biomass. Soil samples were taken from grass-legume pasture (GL), continuous rice (CR) and native savanna (SAV) which served as reference. In agreement with estimated P budgets (+277, +70 and 0 kg P ha−1 for CR, GL and SAV, respectively), available P estimated using Bray-2 and resin extraction declined in the order CR > GL > SAV. Increases in Bray-2 and resin Pi were greater in CR than GL relative to total soil P increase. Organic P fractions were significantly less affected by P inputs than inorganic fractions, but were a more important sink in GL than CR soils. Extractable microbial P (Pchl) was slightly higher in GL (6.6 mg P kg−1) than SAV soils (5.4 mg P kg−1), and significantly lowest in CR (2.6 mg P kg−1). Two days after labeling the soil with carrier free 33P, 25, 10 and 2% of the added 33P were found in Pchl in GL, SAV and CR soils, respectively, suggesting a high and rapid microbial P turnover that was highest in GL soils. Indicators of P mineralization were higher in GL than CR soils, suggesting a greater transformation potential to render Po available. Legume-based pastures (GL) can be considered as an important land-use option as they stimulate P cycling. However, it remains to be investigated whether crops planted in pasture-crop rotations could benefit from the enhanced Po cycling in grass-legume soils. Furthermore, there is need to develop and test a direct method to quantify Po mineralization in these system

Unconventional feeds for small ruminants in dry areas have a minor effect on manure nitrogen flow in the soil-plant system

In dry areas, unconventional feeds are increasingly used for mitigating feed shortages and rangeland degradation. We evaluated how feeding sheep diets containing olive leaves, saltbush leaves and olive cake affects manure quality compared to a barley straw based diet. Soil incubation and plant growth experiments were carried out to measure soil nitrogen (N) mineralization and N uptake by barley plants and to calculate N flow through the feed-animal-soil-plant system. Fresh feces, composts consisting of feces, urine and straw, and ammonium sulfate fertilizer were mixed with soil at rate of 90mgNkg−1 soil dry matter. Comparisons were made with non-amended soils (control) and soils amended with fresh olive cake applied at 90 and 22.5mgNkg−1 soil dry matter, respectively. The latter treatment enabled investigation of the effect of passage of olive cake through the digestive tract of sheep on N availability and phenol transformation. Applying fresh olive cake and feces, except the saltbush leaf derived feces, resulted in a net N immobilization. All composts resulted in net N mineralization, although not significantly different from the 0N control soil. Barley growing in soils with amendment that caused N immobilization took up less N than barley growing on the 0N treatment. Reduction in N uptake was most pronounced after amendment with fresh-olive cake. Treatments with net mineralization increased barley N uptake over the 0N treatment with 2-16% of N applied being taken up. Dietary composition had a minor effect on N fertilizer value of either feces or compost, but feces N alone was not an efficient N sourc

Tgfbi/Bigh3 silencing activates ERK in mouse retina.

BIGH3 is a secreted protein, part of the extracellular matrix where it interacts with collagen and integrins on the cell surface. BIGH3 can play opposing roles in cancer, acting as either tumor suppressor or promoter, and its mutations lead to different forms of corneal dystrophy. Although many studies have been carried out, little is known about the physiological role of BIGH3. Using the cre-loxP system, we generated a mouse model with disruption of the Bigh3 genomic locus. Bigh3 silencing did not result in any apparent phenotype modifications, the mice remained viable and fertile. We were able to determine the presence of BIGH3 in the retinal pigment epithelium (RPE). In the absence of BIGH3, a transient decrease in the apoptotic process involved in retina maturation was observed, leading to a transient increase in the INL thickness at P15. This phenomenon was accompanied by an increased activity of the pro-survival ERK pathway

Effects of Agropastoral Systems on Microbially Bound Phosphorus in Low P Acid Soils

The effect of agropastoral systems replacing native savanna on microbially bound phosphorus (Pmic) in low P acid soils was investigated. Chloroform released P (PChl) was measured to estimate Pmic. In a long-term improved pasture experiment, PChl was higher in grass-legume (GL) than grass-only pasture (GO). Although the P balance was slightly higher in GO than in GL, available P contents followed the same trend as PChl suggesting that the presence of legumes enhances the maintenance of P fertility. In a rice-pasture system, PChl was higher than under rice monocrop indicating an effect of the cropping system on PChl that goes beyond P inputs, and includes factors such as soil cultivation, herbicide application and organic matter input. Pmic may not be seen as a factor competing for plant available P in these strongly P-sorbing soils, but as a rapidly cycling pool that protects P from sorption. The results suggest that Pmic is an important indicator of P fertility on low P acid soils

Symbiotic N2 fixation by soybean in organic and conventional cropping systems estimated by 15N dilution and 15N natural abundance

Nitrogen (N) is often the most limiting nutrient in organic cropping systems. N2 fixing crops present an important option to improve N supply and to maintain soil fertility. In a field experiment, we investigated whether the lower N fertilization level and higher soil microbial activity in organic than conventional systems affected symbiotic N2 fixation by soybean (Glycine max, var. Maple Arrow) growing in 2004 in plots that were since 1978 under the following systems: bio-dynamic (DYN); bio-organic (ORG); conventional with organic and mineral fertilizers (CON); CON with exclusively mineral fertilizers (MIN); non-fertilized control (NON). We estimated the percentage of legume N derived from the atmosphere (%Ndfa) by the natural abundance (NA) method. For ORG and MIN we additionally applied the enriched 15N isotope dilution method (ID) based on residual mineral and organic 15N labeled fertilizers that were applied in 2003 in microplots installed in ORG and MIN plots. These different enrichment treatments resulted in equal %Ndfa values. The %Ndfa obtained by NA for ORG and MIN was confirmed by the ID method, with similar variation. However, as plant growth was restricted by the microplot frames the NA technique provided more accurate estimates of the quantities of symbiotically fixed N2 (Nfix). At maturity of soybean the %Ndfa ranged from 24 to 54%. It decreased in the order ORG>CON>DYN>NON>MIN, with significantly lowest value for MIN. Corresponding Nfix in above ground plant material ranged from 15 to 26g Nm-2, with a decreasing trend in the order DYN=ORG>CON>MIN>NON. For all treatments, the N withdrawal by harvested grains was greater than Nfix. This shows that at the low to medium %Ndfa, soybeans did not improve the N supply to any system but removed significant amounts of soil N. High-soil N mineralization and/or low-soil P availability may have limited symbiotic N2 fixatio