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Background: In a long‐term rotation experiment (2016–2022) with different nitrogen (N) fertilizer levels in subtropical South‐India, crop yields of low N plots were unexpectedly high. We therefore hypothesized that in the absence of mineral N application, these yields are largely due to N inputs by N2 fixation in the component crops. To assess the diazotrophic N2‐fixation of lablab (Lablab purpureus L. Sweet) and possible associative N2‐fixation of finger millet (Eleusine coracana L. Gaertn), a controlled experiment was conducted during the 2021 monsoon season within the above‐mentioned long‐term field study. Two approaches were used to estimate the quantity of N derived from the atmosphere (Ndfa): the dilution method using a 15N‐labeled fertilizer and the natural abundance method. Method: For the 15N dilution method irrigated maize (Zea maize L.), finger millet and lablab were labeled with two split applications of 10% 15N fertilizer (50:50 15N‐urea and 15N‐ammonium sulfate) amounting to a total of 15 kg N ha−1. Maize was selected as the non‐fixing reference plant to estimate diazotrophic N2‐fixation. The entire aboveground biomass of the labeled plants was harvested at maturity and analyzed for total DM, N concentration, and the 15N isotope ratio. Results: N2 fixation efficiency for lablab was 52%–69% depending on the calculation method, corresponding to 40–53 kg N ha−1. For finger millet, the natural abundance method resulted in an estimated N2‐fixation of 5 kg N ha−1, which was suggested by the results of the dilution method whereby the reference plant maize was only poorly labeled. Conclusion: Labeling of maize might have been diluted due to unexpected associative N2‐fixation or N‐uptake from unlabeled deep soil N pools. The data underline the importance of symbiotic N2‐fixation in crop rotation systems of South‐India. [ABSTRACT FROM AUTHOR]

There is growing concern that greenhouse gas (GHG) emissions during agricultural energy crop production might negate GHG emission savings. Here a study is presented evaluating two favourable biogas crops in two agro-ecological regions of Northern Germany for their productivity and GHG emissions. A 2-year field experiment was conducted at two sites with different soil type but similar temperate maritime climate. We compared silage maize which is currently the standard crop grown for biogas fermentation purposes to an alternative bioenergy crop at each site. Three forms of fertilizers/manures were given: calcium ammonium nitrate, cattle / pig slurry, biogas waste. GHG emissions of all biogas crops were strongly dominated by N2O emissions. There were very short CH4 emission events immediately after application of slurry and biogas waste. N2O flux patterns usually followed fertilizer application events in all crops and at both sites. Flux patterns indicated pronounced effects of soil moisture which was also seen as responsible for the 20–30 % higher N2O fluxes in maize compared to the other tested crops. Overall, N2O emissions at the loamy soil site were at least 3 times higher than in all crops examined at the site with sandy soil. The present study provides a very good basis for the assessment of direct emissions of greenhouse gases from relevant biogas crops in North-West Europe. It is intended to use measured and simulated data on soil moisture and the N/C inputs by fertilizer/manure application as drivers for a nitrification/denitrification module linked to a crop growth model.

Concentration of mineral elements in rice seeds may vary depending on the soil fertility status and seed polishing (milling). In order to test this, 54 rice varieties were grown in the fields used to cultivate rice either with or without applying fertilizers for over 40 years. Part of the seeds collected from those varieties was polished before using for element analyses using ICP-MS while the rest considered as unpolished seeds. When comparing unpolished rice seeds produced at fertilized and unfertilized sites, the concentrations of Mg, Ca, K, Mn, Co, Cu, As and Cd were decreased, and the concentrations of Na, Al, Fe, Zn, and Mo were unchanged from fertilized to unfertilized sites. When comparing unpolished and polished rice seeds produced at fertilized and unfertilized sites, seed Mg, K, Mn, Fe, Co and Zn concentrations were higher in unpolished seeds than those in polished seeds, and the concentrations of Na, Al, Mo, Cd, As and Pb were similar between polished and unpolished seeds. Estimated values revealed that rice contributed 4–15% of the daily requirement of Fe, Cu, Zn, and 50–60% Mo irrespective of the soil fertility and polishing. Seed concentrations of As, Pb and Cd were lower than the maximum allowable levels. However, rice consumption contributed to the daily intake of 4–8 µg as, 2–6.5 µg Cd, and 19–25 µg Pb. Improving soil fertility is required to enrich rice seeds with most of the micronutrients and the milling should be done with much care to minimize nutrient loss in human diet. [ABSTRACT FROM AUTHOR]

Studies covering combined effects of agronomic management strategies and their interactions for safer rice production in multiple heavy metal [cadmium (Cd) and lead (Pb)] and metalloid [(arsenic (As)] contaminated soil are rare. Therefore, the effectiveness of phosphorus (P) or silicon (Si) addition together with soil water management (flooded or aerobic) in a soil contaminated with multiple heavy metals was tested in a pot experiment for 8 weeks. Growth of rice was retarded under flooding (27%) compared to aerobic conditions, and application of P led to recover the reduction in growth. Aerobic and flooded water managements could decrease 66% As and 84% Cd concentrations in rice tissues, respectively. Applications of P or Si could decrease only 22% As (only under flooded condition) and 24% Cd (only under aerobic condition) in rice tissues. Accumulation of Pb in rice was not observed. Aerobic soil lowered the concentrations of As, Cd and Pb in the soil solution when compared to flooding. Moreover, As and Pb concentrations in soil solution increased with time while that of Cd declined. Appropriate water management was the most efficient in reducing heavy metals and metalloids accumulation in rice seedlings while the effects of P or Si were marginal. [ABSTRACT FROM AUTHOR]