Response of irrigated lucerne to defoliation and nitrogen fertiliser

A 3-year-old stand of lucerne (Medicago media Per.) cv. 'Wairau' was spray irrigated and subjected to three defoliation frequencies from spring to autumn, after which all plots received a common management. Nitrogen fertiliser was applied to half the plots after each defoliation. Total dry-matter yields calculated for a 12-month period were 24.0 and 28.2 tonnes DM/ha, and herbage N yields for control plots and those receiving N were 730 and 860 kg/ha respectively when the lucerne was defoliated at first flower. The highest mean growth rates (150 kg DM ha/day) occurred in midsummer, coinciding with maximum temperatures and radiation. Maximum response to N fertiliser also occurred at this time. Nitrogen fertiliser depressed spring lucerne yields. Defoliation management did not affect short-term N yields, but frequent defoliation reduced dry-matter yields and allowed extensive weed invasion. Nitrogen fertiliser did not affect weed yields

Rendimento de milho em área de integração lavoura-pecuária sob o sistema plantio direto, em presença e ausência de trevo branco, pastejo e nitrogênio Corn yield on no tillage crop-pasture rotation in presence and absence of white clover, grazing and nitrogen

O trabalho experimental foi realizado no campo, na Estação Experimental da Fundação Agrária de Pesquisa Agropecuária (FAPA), em Guarapuava (PR), Brasil, nos anos agrícolas de 1999 e 2000, com o objetivo de verificar a influência da adubação nitrogenada residual na cultura do milho, em Sistema Plantio Direto, cultivado em seqüência, em áreas que no inverno tinham presença e ausência de trevo branco e de animais em pastejo. O delineamento experimental foi o de blocos ao acaso com três repetições. Os tratamentos foram arranjados em parcelas subdivididas. No inverno, nas parcelas, foram aplicados quatro doses de nitrogênio (N-TI = 0, 100, 200 e 300 kg ha-1 de N) e, nas subparcelas, a combinação de presença e ausência de trevo branco e de pastejo (CT = com trevo; ST = sem trevo; CP = com pastejo e SP = sem pastejo). No verão, em cada subparcela proveniente do inverno, foram aplicadas cinco doses de N (N-TV = 0, 60, 120, 180 e 240 kg ha-1 de N), em cobertura, e cultivado o milho. A máxima eficiência técnica de rebrote da cultura de inverno, avaliada dezoito dias após a retirada dos animais, foi obtida com a aplicação de 231 kg ha-1 de N (N-TI). As áreas CP/N-TI apresentaram maiores produtividades do milho que as áreas SP; contudo, estes resultados não foram estatisticamente significativos. As áreas sem N-TI produziram mais milho em subparcelas SP. As parcelas que receberam 300 kg ha-1 de N N-TI não mostraram resposta do milho ao N-TV, comprovando o efeito residual do N-TI. Conclui-se que a interação entre pastejo e N-TI contribui para a nutrição nitrogenada da cultura do milho.<br>This field experiment was carried out at the Fundação Agrária de Pesquisa Agropecuária [Agrarian Foundation for Agricultural and Cattle Research] (FAPA), in Guarapuava, State of Paraná, Brazil, during the growing seasons of 1999 and 2000. The objective was to verify residual effects of nitrogen fertilization on maize crop under a no tillage system, in presence and absence of white clover and grazing animals. The experimental layout was a completely randomized block design with three replications. The treatments were arranged in split-plots. Four N rates (N-TI = 0, 100, 200, and 300 kg ha-1 of N) were previously applied on the main plots during the winter season, while the treatments of the sub-plots consisted in combinations of presence and absence of white clover and grazing (CT = with clover; ST = without clover; CP = with grazing, and SP = without grazing). During the summer each sub-plot that had been prepared during the winter was cultivated with corn which received five N rates (N-TV = 0, 60, 120, 180, and 240 kg ha-1 of N) top dressed. The maximum re-growth efficiency of winter culture plants occurred eighteen days after the animals had been removed from the plots, obtained with 231 kg ha-1 of N (N-TI). The areas CP/N-TI presented higher corn yields than the SP plots, although these differences were not statistically significant. The areas without N-TI produced most in the SP subplots. On plots that had received 300 kg ha-1 of N N-TI there was no response of corn to the N-TV, confirming the residual effect of N-TI. The conclusion was drawn that the interaction between grazing and N-TI contributes to nitrogen nutrition in maize