A comparison of winter wheat yield and quality under uniform versus spatially variable fertilizer management

Variabilidade espacial da estabilidade de agregados e matéria orgânica em solos de relevos diferentes

“…A variabilidade dos solos tem sido abordada pela classificação numérica, por métodos de estatística multivariada, classificação contínua (fuzzy), geoestatística, métodos fractais, morfologia matemáti-ca e teoria do caos (Burrough et al, 1994). Embora estes métodos estatísticos permitam inferir sobre a variabilidade espacial do solo (vertical e horizontal), a dependência espacial entre as amostras somente pode ser modelada por meio da geoestatística (Mulla et al, 1992;Webster, 2000). Análises estatísticas clássicas que consideram a independência entre as amostras, baseadas na média, vêm sendo substituídas por análises geoestatísticas fundamentadas na teoria das variáveis regionalizadas (Isaaks & Srivastava, 1989), por intermédio do semivariograma e da dependência espacial.…”

“…Quanto maior o número de amostras, mais alto é o ônus financeiro para o agricultor, e, portanto, o método da geoestatística é uma alternativa na otimização deste processo (Mulla et al, 1992). O conhecimento das relações entre solo e a posição da paisagem definida no espaço e no tempo pode subsidiar levantamentos de solos (Marques Júnior & Lepsch, 2000).…”

Effect of nitrogen fertilization and topography on soft red winter wheat yield and protein content in two Ontario landscapes

“…This increased biomass production has in turn resulted in greater SOC content, which contributes to a greater available water content in the soil, potentially mineralizable N, and soil profile development. Lower yields and available moisture on the upper slope position generally result in higher grain protein concentrations in winter wheat (Mulla et al 1992;Manning et al 2001b). Thus, the use of topography to aid in the delineation of N management units is appealing as it would identify some of the more significant changes in soil characteristics in a field, as well as being a method of delineation to which producers can readily relate from a crop production viewpoint.…”

“…Both yield and grain quality vary within a field (Mulla et Mulla et al (1992) indicated that N could be variably applied to wheat based on soil productivity levels associated with moderately to severely eroded soil. It is not known how well yield potential would predict the fertilizer N requirement of wheat in landscapes displaying less evidence of erosion.…”

“…In this case producers are more likely to select fertilizer N rates that minimize the spatial or temporal occurrence of N limitation and therefore result in a greater proportion of the field being over-fertilized. Studies that have compared normal producer practices with site-specific N management systems for wheat often demonstrate substantial reductions in fertilizer N applications with little or no impact on yield level (Mulla et al 1992;Bhatti et al 1998). However, as indicated by Flowers et al (2004), much of the reduction in fertilizer N requirement of wheat compared with a producer's normal practice may not be due to variable application of N, but rather a better field-based assessment of the crop's fertilizer N requirement for that year.…”