Double-annual forage crop rotation controls nutrient surpluses in nitrogen-based organic fertilization

Abstract

The use of organic fertilizers from stock-raising activity is usually based on nitrogen (N) criterion. The objective of our research is to evaluate whether this N criterion lead to positive or environmentally risky changes, mainly in organic carbon (OC) storage and the availability of the main nutrients. Three biennial rotations of four crops were set up (in a 6-year time-frame). The treatments included a control (no N added), two mineral treatments where 250 kg N ha-1 yr-1 were provided at two different times during the rotation, three cattle manure treatments which provided 170, 250 and 500 kg N ha-1 yr-1 and four treatments in which the two lowest manure rates were complemented with mineral N (80 and 160 kg N ha-1 yr-1). Over the whole 6-year period, the measured soil OC increases were equivalent to ca. 25, 43 and 35% of the manure OC applied respectively, following the manure rate increases. Furthermore, equivalences were of -5, 23 and 25% when compared with full mineral fertilization. The positive slope of phosphorus availability was 1.2 mg Olsen-P kg-1 to 10 kg P ha-1 applied from manures (N:P=4) when starting from a threshold of 15.9 mg Olsen-P kg-1. The availability of other nutrients (Mg, Zn) and Na also increased with rates. In a medium-term experiment, the manure rate of 250 kg N ha-1 yr-1 optimized the nutrient recirculation. In the long-term, rotations should be redesigned to control P surpluses or the amount of N applied from manures should be reduced.

This research was financially supported by several institutions involved in the improvement of fertilization practices in La Garrotxa (NE of Spain). These institutions are Garrotxa Volcanic Zone Natural Park, SIGMA Consortium, IRTA-Mas Badia and Department of Agriculture, Livestock, Fisheries and Food (Generalitat de Catalunya, Catalonia, Spain). This research article received a grant for linguistic revision from the Language Institute of the University of Lleida.