Abstract
Manure is a common source of nitrogen (N) in organic farming. However, manure is not always easily available, while the maximum N amount added as animal manure in organic agriculture is restricted by EU regulations. The present study was designed to test whether green manuring with a warm-season legume and intercropping with a cold-season legume can substitute farm-yard manure or compost as N sources in organic greenhouse tomato crops. To test this hypothesis, a winter-spring (WS) tomato crop was installed in February following the incorporation of crop residues of an autumn-winter (AW) tomato crop intercropped with faba bean, which had been fertilized with cowpea residues as green manure. This treatment, henceforth termed legume treatment (LT), was compared with the use of compost or manure as an N fertilization source in both tomato crops. In addition, a combination of compost and LT was also used as a fourth treatment. The results showed that green manuring with legumes and particularly cowpea can contribute a significant amount of N to the following organic tomato crop, through the biological fixation process. Nevertheless, legumes as green manure, or compost, or their combination cannot efficiently replace farmyard manure as an N fertilization source. Compost exhibited a slow mineralization course.
Highlights
Organic farming has grown significantly over the last two decades
Concentration in dry biomass, the amount of N per unit of cultivated area, the percentage of N derived from the atmosphere (% Ndfa), and the total amount of biologically fixed N
This study confirms that green manuring with legumes and cowpea can contribute a significant amount of N to the organic tomato crop, through biological
Summary
Organic farming has grown significantly over the last two decades. According to Willer and Lernoud [1], during this period the cultivated organic area almost increased sevenfold, while the share of organic cultivation in the total cultivated area increased fivefold. The main reasons for this increase were, on the one hand, the concern of many people about the impact of conventional agriculture on their health and the environment [2], and especially on the pesticide residues in food [3], and on the other hand, the decision of many farmers to turn to organic farming. This can be ascribed especially to the fact that the growers have seen an impasse in conventional cultivation due to soil degradation, reduced soil fertility, and the evolution of pesticide resistance. The application of synthetic chemicals is prohibited for both plant protection and fertilization purposes [4] and only environment-friendly practices, such as crop rotation, enhancement of soil fertility through biological processes, composting, and beneficial biota can be deployed to maintain soil fertility and control pathogens and pests [4,5]
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