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SUMMARYIn order to select soil management practices that increase the nitrogen-use efficiency (NUE) in agro-ecosystems, the different indices of agronomic fertilizer efficiency must be evaluated under varied weather conditions. This study assessed the NUE indices in no-till corn in southern Paraguay. Nitrogen fertilizer rates from 0 to 180 kg ha -1 were applied in a single application at corn sowing and the crop response investigated in two growing seasons (2010 and 2011). The experimental design was a randomized block with three replications. Based on the data of grain yield, dry matter, and N uptake, the following fertilizer indices were assessed: agronomic N-use efficiency (ANE), apparent N recovery efficiency (NRE), N physiological efficiency (NPE), partial factor productivity (PFP), and partial nutrient balance (PNB). The weather conditions varied largely during the experimental period; the rainfall distribution was favorable for crop growth in the first season and unfavorable in the second. The PFP and ANE indices, as expected, decreased with increasing N fertilizer rates. A general analysis of the N fertilizer indices in the first season showed that the maximum rate (180 kg ha -1 ) obtained the highest corn yield and also optimized the efficiency of NPE, NRE and ANE. In the 1642 second season, under water stress, the most efficient N fertilizer rate (60 kg ha -1 ) was three times lower than in the first season, indicating a strong influence of weather conditions on NUE. Considering that weather instability is typical for southern Paraguay, anticipated full N fertilization at corn sowing is not recommended due the temporal variability of the optimum N fertilizer rate needed to achieve high ANE.Index terms: Zea mays, plant nutrition, no-tillage, soil fertility.RESUMO: EFICIÊNCIA DA FERTILIZAÇÃO NITROGENADA APLICADA NA SEMEADURA DO MILHO, AVALIADA SOB CONDIÇÕES CLIMÁTICAS CONTRASTANTES NO PARAGUAI Visando selecionar práticas de manejo que incrementem a eficiência do uso de nitrogênio (EUN) em agroecossistemas, faz-se necessário avaliar vários índices agronômicos de eficiência da fertilização. O objetivo deste trabalho foi avaliar a EUN no milho, sob sistema plantio direto na região Sudeste do Paraguai. Neste trabalho, investigou-se a fertilização integral na semeadura do milho com doses variando de 0 até 180 kg de N, durante duas safras (2010 e 2011). O delineamento foi de blocos ao acaso, com três repetições. Com os dados de produtividade de grãos e matéria seca e o N absorvido, realizaram-se os cálculos dos seguintes índices: eficiência agronômica do uso de N (EAN), eficiência aparente da recuperação de N (ERN), eficiência fisiológica do N (EFN), produtividade parcial do fator (PPF) e balanço parcial do nutriente (BPN). As condições climáticas foram favoráveis ao desenvolvimento da cultura do milho na primeira safra e desfavoráveis na segunda. Os índices PPF e EAN, conforme esperado, apresentaram valores decrescentes em razão do incremento das doses de N. Na análise conjunta dos índices, observou-se, na p...

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Understanding indicators of soil health is crucial for developing agricultural systems that are sustainable and climate resilient. Labile soil carbon (C), microbial properties, and nutrient status are all incorporated into the Haney Soil Health Tool with the goal of summarizing several indicators into one index. Monthly soil samples from an integrated crop–livestock system in Central Texas were collected from 2017 to 2019. Fields represented a range of management practices, including cover crops, no‐till, rotational grazing, and a native prairie remnant. Soil samples were analyzed for total C, water‐soluble C, macro‐ and micronutrient content and bioavailability, and phospholipid fatty acids (PLFAs). Microbial activity was determined via a 24‐h CO2 incubation. Soil health score, C, and PLFAs were well correlated with each other. The greatest total PLFA (219.5 nmol g–1 soil) and organic C (54.3 g kg–1 soil) were found in the native prairie, and the lowest were found in the unfertilized continuous‐corn system (60.5 nmol PLFAs g–1 soil and 24.0 g organic C kg–1 soil). Of all agroecosystems, the perennial grazing system (soil health score, 24.7) was most similar to the native prairie (soil health score, 27.4), having high soil C and a large microbial community. Of the row cropping systems, the no‐till system approached the perennial systems better than the conventional till and unfertilized conventional till (soil health score, 11.1 vs. 8.0 and 5.3, respectively). This study highlights the value of perennial grass grazing in agroecosystems and appropriate best management practices. Expanding this analysis to other sites may provide additional insight.