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Context. An appropriate use of the fertiliser technology may lead to a more efficient N absorption and to the reduction of economic and environmental costs. Aims. This study sought to quantify [N.sub.2]O emissions generated from soil and the residual nitrate (N[O.sub.3.sup.-]) up to 2m depth in field conditions in a maize crop under supplementary irrigation and fertilised with two nitrogen (N) sources (UAN and urea) at increasing N rates (0, 80, 160 and 250 kg N [ha.sup.-1]) in the Semi-arid Argentine Pampas. Methods. Throughout the crop cycle, emissions were monitored daily with static chambers during the first week after fertilisation; then sampling frequency was gradually reduced until the end of the experiment. Key results. There were no yield responses to the use of different sources and N rates. Crop N uptake saturated at 80 kg N [ha.sup.-1], reaching 300-310 kg N [ha.sup.-1]. Residual N[O.sub.3.sup.-] increased significantly with the highest rates of N fertiliser. Total [N.sub.2]O emissions differed significantly only among fertiliser rates. The [N.sub.2]O emissions were lower at 80 than at 160 and 250 kg N [ha.sup.-1]. Conclusions. The [N.sub.2]O emissions measured were lower than those calculated by the IPCC, even when only direct emissions were considered. No grain yield increase was observed due to N fertilisation, with a non-limiting supply of N-N[O.sub.3.sup.-] at the beginning of the crop cycle and of N from mineralisation. Implications. This excess of N can generate negative environmental effects due to higher emissions of [N.sub.2]O and residual N-N[O.sub.3.sup.-] that can be leached. Keywords: Argentinean Pampas, environmental effects, greenhouse gases, irrigation, maize yield, nitrate leaching, UAN, urea., Introduction About 80% of cereal and oilseed production in Argentina comes from the Pampean region, mostly soybean, maize and wheat crops (Klein and Vidal Luna 2021). In 2019, maize production [...]

Abstract: Soil N2O fluxes are frequently assessed by the use of static chambers with a single daily sampling. In this study, two experiments were conducted in two contrasting climatic locations, one in Edinburgh, UK, and the other at Seropédica, Rio de Janeiro State, Brazil. Soil N2O fluxes were monitored every 6 h for 30 days during the summer in Edinburgh by the use of an automatic chamber system, and every 3 h for 5 days at Seropédica, using a manually-sampled static chamber. Air and soil temperatures were also measured at the same time as the N2O fluxes. The principal driver of N2O flux within any diurnal period was found to be soil temperature. Regression analysis showed that, for both places, the evenings (21:00–22:00 h) and mornings (09:00–10:00 h), were the times that the flux best represented the daily mean. The ability to work in daylight make the morning period the preferred one. [Copyright &y& Elsevier]

Abstract: The 15N natural abundance technique is one of those most easily applied ‘on farm’ to evaluate the contribution of biological N2 fixation (BNF) to legume crops. When proportional BNF inputs are high, the accuracy of this technique is highly dependent on an accurate estimate of the 15N abundance of the N derived from N2 fixation (the ‘B’ value). The objective of this study was to determine the influence of soybean variety on ‘B’ value. Plants of five soybean varieties were inoculated separately with two Bradyrhizobium strains (one Bradyrhizobium japonicum and one Bradyrhizobium elkanii) grown in pots of soil virtually free of bradyrhizobia capable of nodulating soybean. The proportion of N derived from BNF (%Ndfa) was estimated in separate pots where a small quantity of enriched 15N ammonium sulphate was added. The %Ndfa was then used with the 15N natural abundance data of the nodulated soybean and non-N2-fixing reference plants, to determine the ‘B’ value for each soybean variety/Bradyrhizobium association. The varieties nodulated by the B. japonicum strain showed significantly greater N content and %Ndfa than those nodulated by the B. elkanii strain, and in all cases the ‘B’ value of the shoot tissue (‘B s’) was higher. The differences in ‘B s’ values between varieties nodulated by the same Bradyrhizobium strain were insignificant, indicating that this parameter is influenced much more by the Bradyrhizobium strain than by the variety of the host plant. [ABSTRACT FROM AUTHOR]