The efficiency of nitrogen in cattle manures when applied to a double-annual forage cropping system

Abstract

Using cattle manure (CM) fertilization, it is challenging to optimize nitrogen use. Our work aimed to assess nitrogen efficiencies, in a six-year experiment which involved three biennial rotations of four crops: oat-sorghum (first year) and ryegrass-maize (second year). This rotation was maintained in a rainfed humid Mediterranean area of Spain. Fertilization treatments included: control (no-N), 250 kg mineral N ha-1year-1 (250MN), three CM rates (170, 250 and 500 kg N ha-1year-1), and four treatments where the two lowest CM rates were complemented with either 80 or 160 kg mineral N ha-1 year-1. The treatments were distributed randomly in each of three blocks. Maximum dry-matter yield (~44-49 t ha-1 rotation-1) was achieved in the third rotation, and only the control and the 170CM yielded significantly less. Inside the limitations of the EU Nitrate Directive, the N steady state of 170CM always requires a mineral complement (80 kg N ha-1) to maximize N agronomic efficiency. The maximum nitrogen fertilizer replacement value (250CM vs. 250MN) was 0.67, without significant differences between the two treatments in other N related efficiency indexes, which indicates that plants took advantage of N residual effects. Nitrogen losses by leaching in the 250CM were around 5-7% of the N applied. This reinforces the sustainability of manure recycling in long cropping seasons.

This research was financially supported by the following institutions involved in the improvement of fertilization practices in La Garrotxa, north-east Spain: Garrotxa Volcanic Zone Natural Park, Consortium SIGMA, IRTA-Mas Badia Foundation and Ministry of Agriculture, Livestock, Fisheries and Food (Generalitat de Catalunya, Catalonia, Spain).