The effect of different olive oil mill waste water and nitrogen doses on cotton (Gossypium hirsutum L.) yield and quality

Olive oil mills wastewater is described as complex waste water that occurs during the process of obtaining oil from olive. Although it contains phenols at toxic levels, it also contains significant amounts of organic material and plant nutrients. In this study, olive oil mills wastewater obtained from lagoons in the form of mud was dried into cake, followed by dilution and application to a test field containing sandy loam soils. Different doses of olive oil mills wastewater in cake form (0, 1.5, 3 t da−1), in combination with different doses of mineral nitrogen fertilizer (0, 5, 10, 15 kg da−1), were tested for their effects on the cotton plant (Gossypium hirsutum L.). Yield and yield components of cotton, fiber quality characteristics, selected nutrient components, and specific physical and chemical soil properties were investigated. It was observed that the olive oil mills wastewater cake at a dose of 1.5 t da−1 gave the highest yield in the first year, with a 12.9 % increase compared with that in the control group. In the second year, a 3.7 % increase in yield at a dose of 3 t da−1 was observed, although it was not statistically significant. Nitrogen fertilizer in combination with olive oil mills wastewater cake significantly affected yield. However, no clear result in terms of quality parameters was observed. Thus, it was determined that olive oil mills wastewater administered in the form of cake approximately a month before the cotton-sowing period does not have any side effects. In addition, some basic information was obtained regarding its use as a mineral fertilizer, comprising mainly nitrogen, phosphorus, and potassium.