Agronomical and environmental evaluation of a long-term experiment with cattle slurry and supplemental inorganic N applications in silage maize

Abstract

During 19 years of research on silage maize grown a fertile sandy loam soil in Flanders, we compared the use of only inorganic nitrogen (S−) with a system of an annual application of dairy cattle slurry (S+, corresponding with an average rate of 180 kg N ha −1 ) supplemented with inorganic fertilizer nitrogen. The objectives were to study the efficiency of slurry-N, to determine the economic optimum of additional fertilizer-N use and to relate this optimum with the local threshold on residual soil nitrate-N. During the last 5 years, the economically optimal fertilizer rates in the S− and the S+ system were centred around 150 and 90 kg N ha −1 , respectively. So, saving on fertilizer N amounted to about 60 kg N ha −1 . At these N rates, the risk for trespassing the local legal threshold value for residual soil nitrate-N content (90 kg ha −1 , 0-90 cm) was small (less than one out of ten seasons); economic and ecological optima of N fertilization concurred well. Meeting the standards of the EU nitrates directive and/or a doubled fertilizer N price would urge to decrease the applied amount of inorganic N by ca. 50 kg ha −1 , resulting in yield losses of about 5% on the studied sandy loam soil with an important content of total N (5300 kg ha −1 , 0-30 cm). The ratio of N-fertilizer replacement to the total amount of applied slurry-N increased during the experimental period to an average level of 59% during the last 5 years.

Nitrate leaching from liquid cattle manure compared to synthetic fertilizer applied to grassland or silage maize in the Netherlands

“…The results of Nevens and Reheul (2005) show that adjustment of supplementary CAN fertilization to the level of organic N mineralization (a strategy applied in the Netherlands) can mitigate the risk of increased leaching due to accumulation of organic N.…”

“…At this application level, every 100 kg total N applied was associated with an additional 3-4 kg autumn SMN (Ten Berge et al 2002). However, repeated large applications of organic N will over the years result in an increase in the level of soil organic N and organic N mineralization, until a steady state is reached (Ten Berge et al 2002;Nevens and Reheul 2005). Therefore, the level of supplementary CAN application has also to be reduced over the years, to account for this increase in plant-available N (Ten Berge et al 2002;Schröder et al 2010).…”

“…Other fodder crops have a much longer N uptake period over the growing season; for instance fodder beet (Beta vulgaris L.) absorbs N into late autumn and the level of annual N uptake can approach 500 kg N ha -1 -year -1 (Nevens and Reheul 2005), close to N uptake capacity of permanent grassland (Ten Berge et al 2002).…”

Dose optimale économique d’azote et nitrates du sol après la récolte du canola

“…Les quantite´s de nitrates re´siduels mesure´es dans le profil de sol en fin de saison de croissance sont fortement influence´es par les quantite´s de nitrates provenant des engrais mine´raux azote´s applique´s au semis (Be´langer et al 2003;Nevens et Reheul 2005;Hong et al 2007). Des augmentations de la quantite´de nitrates du sol a`la re´colte ont e´te´mesure´es a`la suite d'application d'engrais azote´au printemps dans la culture de canola (Giroux et al 2000).…”

“…Afin de re´duire les risques d'accumulation de la quantite´de nitrates dans le profil de sol apre`s la re´colte, l'utilisation de la dose optimale e´conomique d'azote a e´te´sugge´re´e comme outil de gestion de la fertilisation azote´e (Be´langer et al 2003;Nevens et Reheul 2005). Cette approche peut eˆtre toutefois risque´e car les diminutions des apports d'azote permettent effectivement de re´duire la quantite´de nitrates re´siduels du sol mais peuvent e´galement re´duire le potentiel de rendement (Dinnes et al 2002).…”