Efficiency of nitrogen fertilizer applied at corn sowing in contrasting growing seasons in Paraguay

• Published in: Revista Brasileira de Ciência do Solo 2013-12, Vol.37 (6), p.1641-1650
• Main Authors: Amado, Telmo Jorge Carneiro, Hahn Villalba, Enrique Oswin, Bortolotto, Rafael Pivotto, Santi, Antônio Luis, Benítez León, Enrique Asterio, Menefee, Dorothy, Kunz, Junior
• Format: Article
• Language: English
• Subjects: fertilidade do solo; nutrição de plantas; plantio direto; SOIL SCIENCE; Zea mays
• ISSN: 0100-0683; 1806-9657; 0100-0683
• DOI: 10.1590/S0100-06832013000600020

In 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 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. 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