Improvement of soil properties and nitrogen utilisation of sunflower by amending municipal solid waste compost

We studied the effects of municipal solid waste compost applied to soil on sunflower nitrogen (N) uptake, N utilisation, yield, soil mineral N deficit and soil characteristics. One unfertilised control was compared with the optimal N dose for the sunflower crops in the test area (100 kg N ha(-1)) supplied as: organic fertilisation, with municipal solid waste compost; mineral fertilisation, with ammonium nitrate; and mixed fertilisation, with 50 kg N ha(-1) from compost and 50 kg N ha(-1) from mineral nitrogen. The results obtained showed that the compost, at the end of the experiment, modified the soil chemical properties. In particular, it significantly improved available phosphorus (111.3% increase for compost treatment in respect to 57.6% for the control), maintained almost the same level of exchangeable potassium (6.0% reduction for compost treatment in respect to 9.8% for the control), and significantly enhanced total soil organic matter (50.0% vs. 32.1%) and extracted organic carbon (16.6% vs. 11.8%). In addition, the application of this material did not increase the total content of heavy metals. The results showed that the municipal waste compost did not modify N uptake, utilisation, or efficiency of sunflower plants. The mean value of N uptake during the vegetative stage was 60.9%, while postanthesis N uptake reached only 39.1% and was positively and significantly correlated with yields and total N uptake, showing that the late N absorption could influence yield performance of sunflower cropped in Mediterranean conditions. Furthermore, the compost, alone or in association with mineral fertiliser, allowed similar yield performance as mineral fertilisation in oil yield (1.51, 1.48 and 1.58 t ha(-1), for the three treatments, respectively) and protein yield (0.66, 0.64 and 0.65 t ha(-1), respectively).