Effects of delayed hay removal on the nutrient balance of roadside plant communities.
Weight and nutrient losses from fresh roadside cuttings were studied in the field in the Netherlands during a 6-week period between 24 May and 6 July 1993. Large amounts (over 50%) appear to be lost from the cuttings. The losses were positively related to initial nutrient concentrations during this short-term study. Weight and nitrogen losses were best explained by the initial C:N ratio, phosphorus and potassium losses by the initial phosphorus concentration. For potassium the losses were particularly large (up to 90%). For this element only, the observed relationship between loss rate and initial chemical composition could not be established significantly. It is concluded that potassium is mainly lost by leaching whereas the major nitrogen, phosphorus and mass losses are most probably caused by rapid microbial decomposition of readily soluble substances. Using existing data on chemical composition of other roadside cuttings, nutrient losses after different hay removal delay times were modelled for different plant communities. All or most of the losses were assumed to return to the soil system. When soil impoverishment is aimed for, it is suggested that cuttings should be removed within 1 or 2 weeks in most plant communities. If removal is delayed longer, the amounts of nutrients removed will often fall below the annual atmospheric input. In plant communities where annual above-ground production of nitrogen and phosphorus are lower than the annual atmospheric deposition already, rapid removal of the cuttings may be the only way to maintain at least potassium at a limiting level. The main effect of hay-making on the soil nutrient status most likely consists of a reduction of the potassium availability, at least on sandy soils with a low cation exchange capacity and provided there is little delay in hay removal.