Carbon and nitrogen management for the sustainability of organic horticulture
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2016
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Os ensaios de campo no modo de produção biológico são necessários para melhorar as recomendações de fertilização e aumentar as produções neste modo de produção. Com estes objectivos realizou-se uma rotação trianual, num solo franco-arenoso, com uma cultura de cobertura outono/invernal de centeio e ervilhaca para adubação verde nos três anos de rotação, seguida de batata e alface (1º ano), acelga e nabo (2º ano), e penca e cenoura (3º ano). Esta rotação foi delineada com um arranjo de blocos casualizados com adubo verde (GM), GM com 20 e 40 t ha-1 de compostado (C20 e C40), GM com 1 e 2 t ha-1 de adubo orgânico comercial e um tratamento de controlo sem aplicação de fertilizantes para determinar a acumulação de azoto (N) e a produção das culturas. A mineralização de N foi determinada através de uma incubação de campo tendo sido encontrada uma correlação positiva entre o somatório da mineralização de N nos vários períodos de incubação e a produção das culturas durante o período de crescimento destas, prevendo que a incubação de campo pode ser um bom indicador para a fertilização das culturas.
A produção de alface, nabo e cenoura aumentou 90%, 115% e 56% respectivamente com o tratamento C40 em comparação com os tratamentos CF1 e CF2 em virtude da rápida mineralização de N do adubo comercial ocorrida na cultura anterior, diminuindo a disponibilidade de N para a 2ª cultura da estação. Pelo contrário a mineralização de N do composto ocorreu ao longo da rotação diminuindo o risco de perdas de N. A produção de batata foi semelhante nos tratamentos C40, CF1 e CF2 devido à maior disponibilidade de N do compostado na cultura de ciclo-longo da batata (124 dias) na qual a remineralização de N aumentou após 71 dias de imobilização. Pelo contrário, a produção de acelga aumentou com o tratamento CF2 em relação ao tratamento C40 devido ao curto período de crescimento da acelga (54 dias). Provavelmente seria vantajoso atrasar a plantação da acelga devido ao periodo de imobilização de N de 31 dias com C40 de modo a aumentar a sincronização entre a mineralização de N e a absorção de N pela acelga. No 3º ano de rotação as produções idênticas da couve penca nos tratamentos CF2 e C40, apesar desta ser uma cultura de ciclo-curto (56 dias), poderá dever-se à aplicação continuada de compostado e adubação verde que aumentou a disponibilidade de N.
O teor total de N, P e K disponíveis no solo foram semelhantes no início e no fim da rotação com o tratamento C40. Pelo contrário, estes teores de nutrientes diminuíram com os restantes tratamentos após 3 anos de fertilização. O pH aumentou de 4.9 para 6.7 após a aplicação da calagem no ínicio da rotação, diminuindo para 6.1 no fim do ensaio. O C total não aumentou após 3 anos de aplicação de fertilizantes orgânicos, e não se verificaram diferenças significativas entre os vários tratamentos. No entanto, o permanganato de C oxidável aumentou com o tratamento C40 em relação aos restantes tratamentos, revelando o potencial do tratamento C40 para aumentar o sequestro de C no solo. Resumindo, a aplicação de 40 t ha-1 de composto e centeio consociado com ervilhaca durante uma rotação de 3 anos em horticultura biológica demonstrou potencial para: (i) aumentar a produção das culturas; (ii) diminuir o risco de perdas de N; and (iii) aumentar o sequestro de C no solo.
A mineralização de C e N foram determinadas numa incubação de laboratório para avaliar as dinâmicas de C e N dos fertilizantes orgânicos incorporados no solo e comparar as diferenças de mineralização de N durantes as incubações no campo e no laboratório. A taxa de mineralização de N, a acumulação de N e as curvas de mineralização de N do compostado e adubo verde foram diferentes nas incubações de campo e laboratório. No entanto, a taxa de mineralização e a acumulação de N com o adubo orgânico comercial foram idênticas em ambas as incubações.
Improved fertilizer recommendations based on experimental data are required to increase organic crop yields. With this aim a three year field organic crop rotation was set up in a sandy loam soil with a cover crop of rye consociated with vetch over the autumn/winter for green manure, followed by potato and lettuce (1st year), Swiss chard and turnip (2nd year), and Portuguese cabbage and carrot (3rd year). This rotation was arranged as a randomized block design with green manure (GM), GM with 20 and 40 t ha-1 farmyard compost manure (C20 and C40), GM with 1 and 2 t ha-1 of commercial organic fertilizer (CF1 and CF2) and a control treatment without fertilizers, to access crop yield and N uptake. Nitrogen (N) mineralization was determined by field incubation to ressemble the environmental conditions in the field, having been found a positive correlation between the sum of mineralized N and crop yield during the growth period of the crops, showing that field incubation maybe a good indicator to predict fertilization. N uptake and crop yields were compared to N mineralization in order to develop recommendations to adjust N mineralization to crop needs. Lettuce, turnip and carrot yields were significantly increased 90%, 115% and 56% respectively for C40 compared to CF2, probably because of the rapid N mineralization of the commercial fertilizer during the previous crop, decreasing N availability for the 2nd crop of the season whereas compost N mineralization took place during all crop rotation decreasing the risk of N losses. Differences on potato yield were not found between the treatments C40, CF1 and CF2, probably due to the long potato growth season (124 days) which allowed a better efficiency use of the mineralized N from the compost in which N remineralization increased after 71 days N immobilization. In contrast, Swiss chard, with a much shorter growing season (54 days), presented a yield increase for CF2 compared to C40. Probably, it would be advantageous to delay S. chard plantation due to the period of 31 days N immobilization with C40 to increase synchronization between N mineralization and N uptake. Portuguese cabbage yield, unlike Swiss chard, did not increase for CF2 compared to C20 and C40 in the 3rd year crop rotation, even with the same short growth period (56 days), probably due to the effect of continuous compost and green manure application that increased N availability in the long-term. The amount of total N and extractable P and K in soil decreased for GM, C20, CF1 and CF2 whereas these nutrient contens were similar for C40 after 3 years of organic fertilization. The pH increased from 4.9 to 6.7 after liming and decreased to 6.1 in the end of the experiment. Total C did not increase after three years of accumulated application of organic fertilizers and there were no significant differences between treatments. However, the permanganate oxidizable carbon content increased for C40, indicating greater impact on C sequestration. Briefly, the application of 40 t ha-1farmyard manure compost and rye consociated with vetch as green manure during three years of organic horticultural crop rotation has the potential to (i) enhance crop yields; (ii) decrease the risk of N losses; and (iii) increase C sequestration. C and N mineralization were determined by laboratory incubation to assess C and N dynamics after organic fertilizers incorporation into the soil and to argue about N mineralization differences in field and laboratory incubations. Compost and green manure N mineralization rate, accumulated mineralized N and the pattern of N released were different in field and laboratory incubations. However, N mineralization rate and the accumulated mineralized N were similar with commercial fertilizer incorporation in both incubations.
Improved fertilizer recommendations based on experimental data are required to increase organic crop yields. With this aim a three year field organic crop rotation was set up in a sandy loam soil with a cover crop of rye consociated with vetch over the autumn/winter for green manure, followed by potato and lettuce (1st year), Swiss chard and turnip (2nd year), and Portuguese cabbage and carrot (3rd year). This rotation was arranged as a randomized block design with green manure (GM), GM with 20 and 40 t ha-1 farmyard compost manure (C20 and C40), GM with 1 and 2 t ha-1 of commercial organic fertilizer (CF1 and CF2) and a control treatment without fertilizers, to access crop yield and N uptake. Nitrogen (N) mineralization was determined by field incubation to ressemble the environmental conditions in the field, having been found a positive correlation between the sum of mineralized N and crop yield during the growth period of the crops, showing that field incubation maybe a good indicator to predict fertilization. N uptake and crop yields were compared to N mineralization in order to develop recommendations to adjust N mineralization to crop needs. Lettuce, turnip and carrot yields were significantly increased 90%, 115% and 56% respectively for C40 compared to CF2, probably because of the rapid N mineralization of the commercial fertilizer during the previous crop, decreasing N availability for the 2nd crop of the season whereas compost N mineralization took place during all crop rotation decreasing the risk of N losses. Differences on potato yield were not found between the treatments C40, CF1 and CF2, probably due to the long potato growth season (124 days) which allowed a better efficiency use of the mineralized N from the compost in which N remineralization increased after 71 days N immobilization. In contrast, Swiss chard, with a much shorter growing season (54 days), presented a yield increase for CF2 compared to C40. Probably, it would be advantageous to delay S. chard plantation due to the period of 31 days N immobilization with C40 to increase synchronization between N mineralization and N uptake. Portuguese cabbage yield, unlike Swiss chard, did not increase for CF2 compared to C20 and C40 in the 3rd year crop rotation, even with the same short growth period (56 days), probably due to the effect of continuous compost and green manure application that increased N availability in the long-term. The amount of total N and extractable P and K in soil decreased for GM, C20, CF1 and CF2 whereas these nutrient contens were similar for C40 after 3 years of organic fertilization. The pH increased from 4.9 to 6.7 after liming and decreased to 6.1 in the end of the experiment. Total C did not increase after three years of accumulated application of organic fertilizers and there were no significant differences between treatments. However, the permanganate oxidizable carbon content increased for C40, indicating greater impact on C sequestration. Briefly, the application of 40 t ha-1farmyard manure compost and rye consociated with vetch as green manure during three years of organic horticultural crop rotation has the potential to (i) enhance crop yields; (ii) decrease the risk of N losses; and (iii) increase C sequestration. C and N mineralization were determined by laboratory incubation to assess C and N dynamics after organic fertilizers incorporation into the soil and to argue about N mineralization differences in field and laboratory incubations. Compost and green manure N mineralization rate, accumulated mineralized N and the pattern of N released were different in field and laboratory incubations. However, N mineralization rate and the accumulated mineralized N were similar with commercial fertilizer incorporation in both incubations.
Descrição
Tese de Doutoramento em Ciências Químicas e Biológicas
Palavras-chave
Agricultura biológica , Composto , Azoto , Mineralização , Incubação de campo , Incubação de laboratório