Browsing by Subject "Fertilization strategies"

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The challenge to achieve a balanced fertilization management in intensive organic vegetable production – approaches for improvement
(2024) Stein, Sophie; Möller, Kurt
The nutrient supply – especially in stockless farms – is a major challenge for organic vegetable farms. Due to the lack of animal husbandry, the nutrient cycle within the farm is limited. At the same time, the nutrient flows in vegetable growing are very high due to the high nitrogen (N) and potassium (K) requirements of the crops. If the nutrient flows are not adapted to the needs of the crops, severe nutrient imbalances, yield or quality losses can occur. Fertilization with basic fertilizers such as manure or compost, based on the N-demand of the crops, can lead to an accumulation of phosphorus (P) in the soil in the long term. Fertilization with N-rich organic commercial fertilizers, on the other hand, is to some extent contradictory to the principles of organic farming due to their origin – mostly from conventional animal husbandry. Another possibility for the exclusive N supply of the farm is the targeted use of legumes with the ability for biological N-fixation (BNF). However, since the cultivation of fodder legumes or grain legumes plays a minor role in vegetable production without livestock, their use for fertilizer management is limited. The aim of this thesis was to optimize fertilizer management in vegetable production based on balanced nutrient budgets of the three main nutrients N, P and K, as well as to increase the supply of N within the farm through the N-fixation of legumes. In a farm survey, the status quo of nutrient management was determined and analyzed using nutrient budgets. In two systemic field trials, the contribution of the strategies legume winter cover crop and living mulch to the on-farm N supply was tested. The status quo of the budgets on organic vegetable farms without livestock shows average budget surpluses of 67.5 kg N ha-1, 2.06 kg P ha-1 and 0.26 kg K ha-1. Another result is that an increase in the N content of base fertilizers such as solid manure or champost leads to an increase in the P and K balance. In the long term, such a strategy carries the risk of nutrient enrichment in the soil. Strategies based on the use of large amounts of keratin fertilizers, on the other hand, have the opposite effect, namely a long-term depletion of P and K. The integration of legumes into the vegetable crop rotation shows that both strategies – leguminous winter cover crops as a preceding crop to white cabbage and leguminous living mulch in combination with white cabbage – lead to similar or even slightly higher cabbage yields than cultivation without legumes or green cover. The direct N-effect of the leguminous winter cover crop on the first crop of white cabbage is about 2/3 of the total N-effect, the N-effect on the second crop of winter wheat is about 1/3 of the total N-effect of the BNF. In the case of the living mulch biomass, which is only incorporated after cabbage cultivation, the direct N effect of BNF on the first main crop is less than 40 %. The N effect on the subsequent winter wheat crop is over 60 %. The results of this thesis show that organic vegetable farms face at least two major challenges in terms of nutrient management: They must implement nutrient management that ensures a balanced nutrient budget in the soil and on the farm while reducing N surpluses through more efficient use of internal and external N sources. This thesis provides important figures for the characterization and balancing of nutrient management in vegetable production. These figures can be used to address the challenge of balanced fertilization management.