Alfalfa yield and quality as function of nitrogen fertilization and symbiosis with Sinorhizobium meliloti

Abstract

The efficiency of the symbiotic process between alfalfa (Medicago sativa L.) and Sinorhizobium meliloti can be drastically affected by soil nitrogen. This research evaluates how mineral fertilization affects the contribution of symbiosis to the yield and quality of alfalfa in two experiments under controlled conditions, and a third one in the field. Under controlled conditions, positive effect of nitrogen fertilizer was observed, whereas, in the field, negative effect of the mineral nitrogen (450 kg ha -1 year -1 ) on the symbiotic process was observed, with reduction of nodulation and nitrogenase activity. However, there was no effect on yield, total nitrogen concentration, crude protein, non-protein nitrogen and digestibility in relation to the treatment without mineral N. The cultivars showed similar performance under different conditions, with 'Crioula Brasileira' and 'Crioula Chilena' showing the highest yield and 'Pioneer-5454' the highest forage nutritive value. Key words: Medicago sativa L., biological nitrogen fixation PRODUÇÃO E QUALIDADE DE ALFAFA EM FUNÇÃODA ADUBAÇÃO NITROGENADA E DA SIMBIOSE COM Sinorhizobium meliloti RESUMO: A eficiência do processo simbiótico entre a alfafa (Medicago sativa L.) e a bactéria Sinorhizobium meliloti pode ser afetada pela presença de nitrogênio no solo. Avaliou-se a contribuição da simbiose em comparação à adubação nitrogenada em componentes da produção de alfafa, em dois experimentos sob condições controladas e um terceiro em campo. Sob condições controladas, verificou-se efeito positivo da adubação nitrogenada sobre as variáveis estudadas, sobre a produção de matéria seca, teor de nitrogênio e proteína. Em campo, verificou-se efeito negativo do N-mineral (450 kg ha -1 ano -1 ) sobre o processo simbiótico, com redução da nodulação e atividade da enzima nitrogenase, sem efeito sobre a produção de matéria seca, nitrogênio total, proteína bruta, nitrogênio não protéico e digestibilidade. O desempenho dos cultivares estudados foi semelhante nos dois ambientes de estudo, sendo os cultivares Crioula Brasileira e Crioula Chilena os mais produtivos e o cultivar Pioneer-5454 como o de melhor valor nutritivo da biomassa produzida. Adubação nitrogenada é dispensável para Medicago sativa inoculada com a bactéria fixadora de nitrogênio correspondente, uma vez que a simbiose pode garantir o fornecimento de nitrogênio em quantidade suficiente para a produção. Palavras-chave: Medicago sativa L., fixação biológica do nitrogênio

Effect of Increasing Doses of Mineral Nitrogen Fertilization on Chemical Composition of Lucerne (Medicago Sativa L.) Under Optimum Water Supply and Water Deficiency Stress

“…With increasing doses of mineral nitrogen fertilization crude protein content increased by 13 to 19%. Our results do not support suggestion that mineral nitrogen fertilization had no effect on the concentration of nitrogen and crude protein content in lucerne [OLIVEIRA et al, 2004] . With increasing doses of mineral nitrogen fertilization under water deficiency stress crude protein content increased significantly by 6 to 14%.…”

Biofertilizante na qualidade nutricional da alfafa (Medicago sativa L.)

“…We observed lower N values than Oliveira et al (2004) who evaluated N in alfalfa cultivars in green house experiments and found higher N concentrations in plants treated with the highest dose (16 mmol N L -1 ); however, they did not detect differences between cultivars. Another factor that could have caused such low N concentrations in our experiment soil pH index which was slightly lower at the end of the experiment than the value of 6.8 recommended by Honda and Honda (1990); low pH values can damage N 2 fixation efficiency in Sinorhizobium meliloti.…”

“…Lloveras et al (2000) also found no significant difference in the concentration of crude protein in an alfalfa experiment with an N application of 30 kg ha -1 yr of nitrogen; however, the protein concentration was higher (20.04 to 23.58%). Oliveira et al (2004) found significantly higher N concentrations in an experiment using nitrogen rate eight times higher than the control in the greenhouse; however, they found no significant difference in a field experiment with applications of 450 kg nitrogen ha -1 yr -1 . Means followed by different capital letters differ significantly by Duncan´s test at 5% probability.…”

Influence of harvest season, cutting frequency and nitrogen fertilization of mountain meadows on yield, floristic composition and protein content of herbage

“…Although legumes are able to use available soil N, they appear to be outperformed by grasses in the competition for that nutrient in grass-clover mixed swards due to their shorter root system (Wilman & Fisher, 1996). Additionally, there is evidence of detrimental effects of N supply on the nitrogen fixing bacteria of the nodulated legumes (Carlsson & Huss-Danell, 2003;Oliveira et al, 2004). All these factors could explain the decrease in legume proportion and, consequently, in CP content of the herbage collected in the regrowths associated to the application of a higher amount of N fertilizer (Tables 2 and 3).…”