Abstract
An organic greenhouse crop of tomato was established in February following cultivation of cowpea (CP) or common bean (CB) for green pod production, or faba bean (FB) for green manuring. The vegetative residues of CP and CB were incorporated to the soil together with farmyard manure (FYM), prior to establishing the tomato crop. The FB plants were incorporated to the soil at anthesis together with either FYM or composted olive-mill waste (CO). Green manuring with FB resulted in higher soil mineral N levels during the subsequent tomato crop and higher tomato fruit yield when combined with FYM, compared to compost. The level of soil mineral N was the main restrictive factor for yield in organic greenhouse tomato. FB for green manuring as preceding crop to tomato increased significantly the level of soil mineral N and tomato yield compared to CB or CP aiming to produce green pods. The lowest tomato yield was obtained when the preceding crop was CB cultivated for green pod production. The soil mineral N was significantly higher when FYM was applied as base dressing compared with CO, despite the higher total N concentration in CO, pointing to slower mineralization rates of CO during tomato cultivation.
Highlights
The aboveground fresh and dry biomass of cowpea or common bean were significantly lower than the corresponding fresh and dry faba bean biomass incorporated into the soil as green manure
The pod harvest index of common bean was significantly higher than that of cowpea on fresh weight basis but similar between the two legumes when calculated on dry weight basis
The major factor contributing to this large difference in dry biomass between faba bean and the other two legume crops was plant density, which was almost threefold in the faba bean plots destined for green manuring (11.7 plants m−2 ) compared to that applied in the crops of common bean and cowpea (4.27 plants m−2 )
Summary
According to most researchers and practical experience, there is a yield gap of more than 20% between organic and conventional farming [2,3,4]. This difference in yield performance probably represents the most important limitation to the further expansion of organic farming [5]. The use of industrially produced fertilizers of inorganic N is prohibited [3]. In many countries and throughout the European Union, the use of inorganic N in organic agriculture is not allowed, even if it is of mineral origin [8]
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