Effects of fertilizer nitrogen and cropping systems on the availability of nitrogen for corn production in Iowa

Studies were conducted to acquire a better understanding of the effects of fertilizer nitrogen and cropping systems on the availability of nitrogen for corn (Zea mays L.) production in Iowa. The availability of nitrogen for corn production was assessed by analyzing soil samples collected when corn plants were 15 to 30 cm tall. The distributions of nitrate found in the soil profiles at this time were surprisingly similar in that the highest concentrations of nitrate always occurred in the top 15-cm layers of soils, and concentrations gradually decreased with increasing depth below the surface. This finding supports recent ideas that nitrate movement in soils is strongly influenced by preferential movement of water through soil macropores.;Amounts of nitrate found in the surface 30-cm layers of soils at this time were highly correlated with corn yields. This finding indicates that a late-spring soil test for nitrate has great potential as a practical tool to determine fertilizer nitrogen needs at sidedressing.;Differences in yields observed between corn after corn and corn after soybean (Glycine max L.) were largely explained by nitrogen effects. When expressed in fertilizer equivalents, the amounts of nitrogen carried over from soybean to corn exceeded the amounts indicated by the late-spring soil nitrate test. The differences in yield could be explained by considering the amounts of nitrogen required to decompose corn residues and the amounts released during decomposition of soybean residues. These observations suggest that continuous corn and corn in rotation with legumes need to be treated as separate categories in the late-spring soil test.;Analysis of soils from long-term rotation-fertility experiments showed that cropping systems and fertilizer nitrogen treatments caused significant differences in the organic nitrogen contents of soils during the past thirty years. The results emphasize a need for greater consideration of changes in soil organic nitrogen content when evaluating the efficiencies and environmental impacts of various cropping systems and fertilization practices

Efeito do nitrogênio em trigo cultivado após diferentes sucessões de culturas

The great majority of the research reported in the literature about the response of wheat (Triticum aestivum L.) to nitrogen (N) was carried out in soils where the previous crop was soybean (Glycine max L.), which can contribute positively, in terms of N, for the following crop. The need to give farmers that grow wheat after corn (Zea mays L.) new information about N management led us to carry out this research, with the following objectives: a) to evaluate the response of wheat to N when grown after corn; b) to determine the effects of different crops, grown the year before, on the wheat crop; and c) to evaluate if there is a residual effect of N levels applied to the previous corn crop. The response of wheat to nitrogen was assessed after four different crop sequences, which had fallow, oats (Avena strigosa Schieb), chickling pea (Lathyrus sativus L.), and common vetch (Vicia sativa L.) as the preceding winter crops and corn as the summer crop. The crop sequences were the treatments and four levels of nitrogen (0, 25, 65 and 145 kg/ha), topdressed on the wheat crop, formed the subtreatments of the split plot arrangement. The experimental design consisted of completely randomized blocks, with four replications. It was estimated that to achieve maximum yields the wheat (cv. BR 23) would need 110 kg/ha of N after the sequence oats/corn, 100 kg/ha of N after fallow/corn and 97 and 89 kg/ha of N after the sequences chickling pea/corn and common vetch/corn, respectively. There was no effect of the preceding winter crops on the wheat crop. No residual effect of the nitrogen levels applied on corn was observed on wheat.A grande maioria dos trabalhos encontrados na literatura brasileira sobre a resposta do trigo (Triticum aestivum L.) a nitrogênio (N) foi conduzida em solos cuja cultura anterior foi a soja (Glycine max L.), que pode contribuir positivamente em N para a cultura seguinte. A necessidade de fornecer informações aos produtores que cultivam trigo após milho (Zea mays L.) levou à execução deste trabalho, que teve como objetivos: a) avaliar a resposta do trigo a N quando cultivado após milho; b) verificar o efeito de diferentes culturas cultivadas no inverno anterior sobre o trigo; c) avaliar o efeito residual de níveis de N aplicados no milho. Estudou-se a resposta do trigo ao nitrogênio após quatro sucessões de culturas, que incluíram pousio, aveia preta (Avena strigosa Schieb), chícharo (Lathyrus sativus L.) e ervilhaca (Vicia sativa L.), no inverno anterior, e milho como cultura antecessora. As sucessões de culturas constituíram os tratamentos, e os quatro níveis de N (0, 25, 65 e 145 kg/ha), aplicados em cobertura no trigo, formaram os subtratamentos do esquema de parcelas divididas, conduzidas no delineamento de blocos casualizados. Estimou-se que, para atingir rendimento máximo, o trigo (cultivar BR 23) necessitaria de 110 kg/ha de N, após a sucessão aveia preta/milho, de 100 kg/ha, após pousio/milho, e de 97 e 89 kg/ha de N, após as sucessões chícharo/milho e ervilhaca/milho, respectivamente. Não se observaram reflexos das culturas do inverno anterior sobre o trigo. Não foi observado efeito residual dos níveis de N aplicados no milho cultivado antes do trigo

Effects of fertilizer nitrogen and cropping systems on the availability of nitrogen for corn production in Iowa

Studies were conducted to acquire a better understanding of the effects of fertilizer nitrogen and cropping systems on the availability of nitrogen for corn (Zea mays L.) production in Iowa. The availability of nitrogen for corn production was assessed by analyzing soil samples collected when corn plants were 15 to 30 cm tall. The distributions of nitrate found in the soil profiles at this time were surprisingly similar in that the highest concentrations of nitrate always occurred in the top 15-cm layers of soils, and concentrations gradually decreased with increasing depth below the surface. This finding supports recent ideas that nitrate movement in soils is strongly influenced by preferential movement of water through soil macropores.;Amounts of nitrate found in the surface 30-cm layers of soils at this time were highly correlated with corn yields. This finding indicates that a late-spring soil test for nitrate has great potential as a practical tool to determine fertilizer nitrogen needs at sidedressing.;Differences in yields observed between corn after corn and corn after soybean (Glycine max L.) were largely explained by nitrogen effects. When expressed in fertilizer equivalents, the amounts of nitrogen carried over from soybean to corn exceeded the amounts indicated by the late-spring soil nitrate test. The differences in yield could be explained by considering the amounts of nitrogen required to decompose corn residues and the amounts released during decomposition of soybean residues. These observations suggest that continuous corn and corn in rotation with legumes need to be treated as separate categories in the late-spring soil test.;Analysis of soils from long-term rotation-fertility experiments showed that cropping systems and fertilizer nitrogen treatments caused significant differences in the organic nitrogen contents of soils during the past thirty years. The results emphasize a need for greater consideration of changes in soil organic nitrogen content when evaluating the efficiencies and environmental impacts of various cropping systems and fertilization practices.</p

Adubação com molibdênio em soja, na presença ou ausência de calcário aplicado na superfície do solo, em plantio direto Molybdenum fertilization, in the presence or absence of lime applied to the soil surface, under no-tillage

Um experimento foi desenvolvido em 1997/1998 em Latossolo Vermelho Distrófico típico, em Passo Fundo, com pH em água 4,9 e 41,2mmol c de Al3+dm-3, para estudar os efeitos de calcário aplicado na superfície do solo, e de molibdênio, sobre o rendimento de grãos da soja. O efeito residual do calcário e a reaplicação de Mo foram estudados no mesmo local, em 1998/1999. O delineamento experimental foi em blocos completos casualizados, com quatro repetições. Os tratamentos foram constituídos por: 1) Mo na semente + calcário; 2) Mo foliar + calcário; 3) calcário; 4) Mo na semente; 5) Mo foliar e 6) testemunha. Aplicaram-se 2t ha-1 de calcário dolomítico. O molibdênio foi aplicado na dose de 12g ha-1, nas sementes, e 30g ha-1 quando via foliar, aos 30-33 dias após a emergência. A soja respondeu à adubação molíbdica, mesmo nos tratamentos com calcário, em ambas as safras. Os resultados indicam que a calagem superficial não disponibilizou molibdênio em quantidades suficientes para o desenvolvimento da soja, cultivada em plantio direto em Latossolo ácido. A aplicação de Mo nas sementes e via foliar tiveram a mesma eficiência.<br>An experiment was carried out in 1997/1998 on Dark Red Latosol (Haplorthox), in Passo Fundo, with pH (H2O) 4.9 and 41.2mmol c de Al3+dm-3, to study the effects of lime, applied on the surface of the soil, and molybdenum, on soybean yields. The residual effect of lime and the reapplication of Mo was studied at the same location, in 1998/1999. The experimental design was the complete randomized block, with four replications. The treatments consisted of: 1) lime + Mo applied on the seeds; 2) lime + foliar application of Mo; 3) lime; 4) Mo applied on soybean seeds; 5) Mo applied on soybean leaves and 6) no lime and no Mo. Lime was applied at a rate of 2t ha-1, at the surface of soil. Molybdenum was applied at the rate of 12g ha-1, on the seeds, and 30g ha-1, when foliar applied, 30-33 days after emergency. Soybean responded to applied Mo, even in the treatments with lime, in both seasons. The results of the two experiments indicated that the superficial application of lime did not release enough Mo for the development of no-tillage soybean in the acid soil used. The fertilization of molybdenum on the seeds or foliar way had the same efficiency

Épocas e métodos de aplicação de nitrogênio em milho cultivado no sistema plantio direto Timing and methods of nitrogen application for corn under no-tillage

O milho (Zea mays L.), no sistema plantio direto, frequentemente é cultivado após cereais de inverno. Durante a decomposição de resíduos culturais pode ocorrer imobilização de nitrogênio (N) e limitação do desenvolvimento da cultura. Visando avaliar métodos de manejo de N sobre a produtividade de milho, cinco experimentos foram conduzidos, durante o período 1997 a 2002, sob sistema plantio direto. Aveia preta (Avena strigosa Schrieb) foi cultivada como cultura de cobertura precedendo o milho, tendo sido dessecada no estádio de antese. O delineamento experimental dos experimentos foi blocos ao acaso, com quatro repetições e com número de tratamentos de 8 a 12. O N foi aplicado em diferentes modos (na superfície, a lanço e incorporado, em linhas) e épocas (em pré-semeadura, na semeadura e na semeadura + cobertura), em dose única de 100kg ha-1, na forma de uréia. No primeiro ano de avaliação (1997/98) ocorreu elevada precipitação pluvial, observando-se rendimentos de grãos maiores nos tratamentos em que o N foi aplicado na semeadura e cobertura, enquanto os demais tratamentos conferiram rendimentos inferiores e semelhantes entre si. Nas safras seguintes, com menor precipitação pluvial do que em 1997/98, não se observaram diferenças significativas entre os tratamentos com aplicação antecipada de N e naqueles com adubação em cobertura, exceto na safra 2000/2001, nos tratamentos com aplicação em pré-semeadura a lanço. Considerando o efeito médio dos tratamentos, observou-se que a aplicação de N alguns dias após a dessecação de aveia preta, totalmente no momento da semeadura de milho, ou na semeadura e em cobertura são práticas viáveis no sistema plantio direto. A incorporação de N em relação à aplicação a lanço, tanto em pré-semeadura, na semeadura ou em cobertura, proporcionou, em média, acréscimos de 5% no rendimento de grãos de milho.<br>Corn (Zea mays L.) is usually cultivated after winter cereals under no-tillage in southern Brazil. During the decomposition of plant residues, nitrogen (N) can be imobilized and limit plant growth. In order to evaluate the effect of timings and methods of N application on corn yields, five experiments were carried out during 1997 to 2002, under no-tillage. Black oat (Avena strigosa Schrieb) was used as a preceding cover crop, beeing desiccated at anthesis. Randomized blocks were used as experimental design, with four replications, and 8 to 12 treatments. N was applied to the soil by different methods (on the surface, broadcasted and incorporated) and timing (before seeding, at seeding, and at seeding + topdressing), at the rate of 100kg ha-1, as urea. At the first year (1997/98), a very high amount of rain fell during the months of September and October, before and shortly after corn emergence. In this season, higher grain yield was obtained by the treatments with topdressed N than by all other treatments, which were lower and similar among themselves. In the subsequent years, with less rainfall, no significant differences were observed among treatments, except in the 2000/2001 season, for the treatments in which N was broadcasted before seeding. Considering the average yield, no differences were observed among the timings of N application. On the average, incorporation of N, at any of the three timings of N application, indicated a tendency to generate about 5 % higher grain yields than soil surface application