Composting is an interesting solution to take advantage of the large quantity of unused resources generated in the agricultural and livestock industry, in addition to the multiple benefits that the use of organic amendments brings to the soils (increase of organic matter, reduction of erosion, possible suppressive effect on pathogens, etc.). We are currently studying the time evolution of three different composts (olive industry residues, greenhouse horticultural crops residues and poultry manure) to appraise the high heterogeneity of compost. This study is being carried out through physico-chemical analysis (moisture, organic matter, C/N ratio, etc.), as well as by near-infrared spectroscopy (NIRS). Our goal is to establish a spectral model of the variation of compost over time. This will give us important information about the stability of some parameters in these organic amendments. Another work that we have accomplished in parallel is the in-field evaluation of the effect of compost from olive industry residues added to a highly degraded soil on Orobanche cumana (broomrape), which is a holoparasite plant of sunflower roots that limits oil production. The experiment has a randomised design with three replications, and compost at three doses: C0 (no amendment), C1 (10 t/ha) and C2 (30 t/ha). In each experimental plot, one bag with O. cumana seeds was buried and extracted 12 months later to evaluate the viability and infectivity of the pathogen. The viability of O. cumana seeds was studied under in vitro conditions and following the methodology used in previous works by our group [1]. Seeds were put in contact with a susceptible sunflower seedling of the cultivar B117 and GR24 (strigolactone analogue that induces broomrape germination) at 0.01 ppm for 21 days at 23 °C. Then, the germination of O. cumana seed was assessed visually using the stereoscopic microscope. In the results obtained we have observed a slight increase in the viability of broomrape seeds for almost all treatments (in the absence of statistical evaluation). The infectivity of O. cumana has been determined in a pot experiment in the greenhouse at 20-25 °C and 12-14 h (night/day) photoperiod, with a duration of 12 weeks. Pregerminated seeds of B117 were sown in soil previously infested with the O. cumana seeds extracted from the field. At the end of the experiment, the infectivity of O. cumana was assessed as the number of nodules attached to the roots, number of broomrapes emerged and height of the plants. The data are currently being statistically analyzed.

Research granted by Project CROPINNO (Stepping up Scientific Excellence and Innovation Capacity for Climate-Resilient Crop Improvement and Production, Grant ID No 101059784) from the European Union Horizon action Widera 2021 Programme, and by Qualifica Project QUAL21-023_IAS from Junta de Andalucía, Spain

[Edtitores] Verónica San Miguel [0000-0001-8014-2452]; Juan I. Padrón Peña [0000-0002-0745-2259]; María Teresa Pérez Prior [0000-0002-6669-1065]; Alberto García-Peñas [0000-0001-5707-0198]

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