Abstract
ABSTRACTThe response of lettuce to production system, organic and phosphate fertilizers and root mycorrhization, was evaluated in two pot trials with factorial treatment combination of: (i) soil type (from organic and from conventional production systems) and organic fertilizer (0, 2 and 4 t ha−1) in the first trial; and (ii) mycorrhizal inoculation (mycorrhized and non-mycorrhized plants) and Gafsa phosphate (0, 100 and 200 kg P2O5 ha−1) in the second. Lettuce growth decreased with increasing rates of the organic fertilizer because of its very high electrical conductivity (50.1 dS m−1) and lack of maturation. However, the fertilizer harmful effects were minimized in the soil from organic production. The application of Gafsa phosphate significantly increased lettuce yield and nutrient uptake. However, for the highest rate of phosphate, mycorrhized lettuce yield decreased compared to non-mycorrhized lettuce, suggesting that high soil available P may have harmful effects on the activity of mycorrhizal fungi.
Highlights
The use of synthetic fertilizers modifies the balance of the soil ecosystem due to changes in soil chemical properties, and to the destruction of the physical properties and reduction of soil biodiversity (Kibblewhite et al, 2008), decreasing the number of species and increasing the contamination of surface and groundwater (Lampkin, 1990)
This study evaluated the effects of an organic fertilizer certified for organic agriculture (OA) applied both to a soil from organic production and to a soil from conventional production, on lettuce growth and nutrient uptake
The high quality of the soil from organic production (SOP) demonstrated ability to withstand disturbances caused by this organic fertilizer, and final lettuce yield significantly increased in this soil compared to soil from conventional production (SCP)
Summary
The use of synthetic fertilizers modifies the balance of the soil ecosystem due to changes in soil chemical properties, and to the destruction of the physical properties and reduction of soil biodiversity (Kibblewhite et al, 2008), decreasing the number of species and increasing the contamination of surface and groundwater (Lampkin, 1990). In contrast to conventional production, organic agriculture (OA) recommends the increased use of on-farm compost and eventually organic fertilizers from outside the farm because these usually have a positive effect on agricultural soils and crop yields. Despite the benefits of amending the soil with organic fertilizers, farmers must consider the amount and quality of the organic amendments because their indiscriminate application may cause phytotoxicity problems (Brito, 2001). P application is recommended in the form of phosphate fertilizers. Natural phosphates with certification for OA can be as efficient as soluble phosphates (Corr^ea et al, 2005) but its efficiency depends on the crop, the rate of application, and soil pH. Natural phosphates are poorly soluble in water and require some acidity of the soil to become soluble over time (Goedert and Sousa, 1984). In a highly acidic soil, the solubility of P decreases due to the precipitation with aluminum, iron and manganese and adsorption with their oxides and hydroxides, and because soil microbial activity and organic matter (OM) mineralization rate decreases
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