Long-Term Manure Application and Forages Reduce Nitrogen Fertilizer Requirements of Silage Corn–Cereal Cropping Systems
2010
Nyiraneza, J. | Chantigny, M. H. | N'Dayegamiye, A. | Laverdière, M. R.
Assessment of the soil N supply capacity is essential to optimize fertilizer N use. We investigated soil N supply capacity and fertilizer N recovery for three cropping systems established in 1977: silage corn (Zea mays L.)–cereal without (CC) and with 20 Mg ha⁻¹ yr⁻¹ manure (CCM), and silage corn–forage (3-yr) with manure (CFM). During the present study (2005–2008), manure applications were suspended and a silage corn–silage corn–barley (Hordeum vulgaris L.)–wheat (Triticum aestivum L.) sequence was imposed to all systems. Fertilizer (¹⁵NH₄ ¹⁵NO₃, 3.1 atom % ¹⁵N) was applied in 2005 to silage corn (160 kg N ha⁻¹) and in 2007 to barley (80 kg N ha⁻¹). The ¹⁵N recovery in silage corn and barley ranged from 40 to 59%, with the lowest values measured in CFM. Compared to the CC systems (47 kg N ha⁻¹) in 2005, soil-derived N in silage corn was two times higher under CCM (98 kg N ha⁻¹), and four times higher under CFM (208 kg N ha⁻¹). These differences decreased over years, but were still noticeable at the end of the experiment. Twenty-two to 58% of applied ¹⁵N was recovered in the soil at harvest. More than 50% of this residual N was present in macroaggregates (>0.25 mm), whereas <20% was present in particulate organic matter (POM). Up to 75% of residual ¹⁵N was lost during the winter period, and little residual N was transferred to the following crop. These findings indicate that soil macroaggregates may be a preferential sink for residual fertilizer N, but this N is not present in stable forms and is vulnerable to environmental loss.
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