E-mail: leonardo.aquino@ufv.br resumo inocular sementes de trigo com Azospirillum brasilense pode ser benéfico à cultura do trigo, bem como reduzir a necessidade de aplicação de n. no entanto, são escassos trabalhos que mensurem o benefício dessa prática no trigo irrigado com expectativa de alta produtividade e demanda de n. objetivou-se com este trabalho avaliar a produtividade e o conteúdo de n na planta do trigo irrigado, submetido a doses de n, com ou sem a inoculação com A. brasilense. Foram conduzidos dois experimentos em 2011 e repetidos em 2012. em cada ano de cultivo, instalou-se um experimento na área considerada de baixa disponibilidade de n no solo (cultivo em sucessão ao milho) e outro na com alta disponibilidade (cultivo em sucessão à soja ou cenoura). Os tratamentos consistiram de cinco doses de N e da inoculação ou não com A. brasilense. as doses de n testadas foram 20, 60, 100, 140 e 180 kg ha -1 na área com baixa disponibilidade de n e 20, 50, 80, 110 e 140 kg ha -1 na com alta disponibilidade. o teor de n na folha índice foi aumentado pela inoculação com A. brasilense. entretanto, o N absorvido não foi influenciado pela inoculação da bactéria. As doses de N aumentaram a produtividade do trigo e esse aumento foi mais evidente no cultivo na área com baixa disponibilidade de n no solo. palavras-chave: Triticum aestivum L., fixação de N 2 , bactérias diazotróficas.Recebido para publicação em 24 de junho de 2014 e aprovado em 7 de outubro de 2014.

Farmers must carefully choose the cultivar to be grown for a successful carrot crop. The yield potential of the cultivar may influence nutrient demand and should be known to plan for fertilization application. The aim of this study was to evaluate the cultivar effect on carrot yield and on the nutrient content and quantities allocated to leaves and roots. Three experiments were set up in two crop seasons in Rio Paranaíba, MG, Brazil. In the first season, typical summer, 10 summer cultivars were sown. In the second season, summer-winter (transition), two experiments were set up, one with summer cultivars and the other with winter cultivars. The treatments consisted of the carrot cultivars distributed in randomized blocks with four replications. Fresh and dry matter of the roots and leaves was quantified. Yield was calculated based on fresh matter of the roots. The nutrient content in leaves and roots was determined at the time of harvest. These contents and the dry matter production of roots and leaves were used to calculate nutrient uptake and export. The greatest average for total and commercial yield occurred in the crop under summer conditions. Extraction of N and K for most of the cultivars in the three experiments went beyond the amounts applied through fertilizers. Thus, there was contribution of nutrients from the soil to obtain the yields observed. However, the amount of P taken up was considerably less than that applied. This implies that soil P fertility will increase after cropping. The crop season and the cultivars influenced yield, nutrient content in the leaves and roots, and extraction and export of nutrients by the carrot crop.

. The four diagnostic methods generated similar reference values of nutrients, but different from those found in the literature. Leaf diagnosis through nutrient content in the shoot at harvest time indicated Mn as the most limiting nutrient for growing carrot, followed by Mg, K, and Ca.

Core Ideas Legumes improved N supply for sweet potato grown subsequently. Mucuna aterrima supply more N to sweet potato than other cover crops. Previous legume cultivation reduces 35.2% the mineral N rate on sweet potato. Higher mineral N rate increased growth of sweet potato vines. Selected cover crops can provide N to sweet potato (Ipomoea batatas [L.] Lam) crops cultivated in succession and reduce the need for mineral N application. This study was conducted to determine the growth, leaf N concentration, N uptake, N removal, storage root yield, and N‐use efficiency of sweet potato crop in response to different cover crop sources and mineral N fertilizer rates. A field experiment was performed over 2 agricultural yr using a randomized complete block design with split‐plots and four replications. Whole plots consisted of four cover crops: One control (spontaneous weeds), two legumes (Crotalaria spectabilis and Mucuna aterrima), and one cereal (Pennisetum glaucum). Subplots consisted of four N rates (0, 50, 100, and 200 kg ha−1) applied to the sweet potato. When no N was applied, M. aterrima supplied more N to sweet potato grown in succession but had the same effect as C. spectabilis on root yield. P. glaucum and spontaneous weeds had the same effect on the N supply and performance of sweet potato. The N rates for the optimum root yield of sweet potato were 49.6 and 76.6 kg N ha−1 when grown after legume and non‐legume species. In tropical conditions, the use of legumes as cover crops reduced the need for mineral N fertilizers by up to 35.2% for sweet potato. The cultivation history of a field should be an important consideration when determining the N fertilization for sweet potato because a high N supply favored the growth of vegetative plant parts.

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Potassium (K) supply affects the growth and tuber yield of potato (Solanum tuberosum L.) as well as the uptake and removal of certain nutrients. However, information on this is scarce or inconsistent. Thus, this study was undertaken to evaluate the dry matter (DM) accumulation and the uptake and removal of nutrients by potato 'Agata' as affected by K fertilizer management (rates and application timings) in tropical clay soils with varied K availability. In soils with low K availability, K fertilization increased (P ≤ 0.05) the biomass of potato plants without differences among management types; however, in soils with medium and high K availability, K fertilizer did not alter the plant DM accumulation. K fertilization increased (P ≤ 0.05) N, K, Ca, Mg, S, B, Mn, and Zn uptake and removal in the soil with low K availability, while in soils with medium and high K availability, K fertilization had less influence on the uptake and removal of nutrients, except that K uptake and removal increased (P ≤ 0.05) under K fertilization, evidencing luxury uptake. In the soil with medium K availability, K application reduced (P ≤ 0.05) Mg uptake by plants, but this effect was not observed in soils with high K availability. Mn uptake and removal increased (P ≤ 0.05) under K fertilization in soils with low and high K availability. The increases in the uptake and removal of almost all nutrients in response to K fertilization were related to the increase in plant DM accumulation, but changes in the concentrations of K and some other nutrients also contributed to their increased uptake and removal.

Potassium (K) is the most taken up and removed nutrient by potato (Solanum tuberosum L.), and has a great influence on tuber yield and quality. This study was performed to evaluate the effects of three rates (100, 200, and 400 kg K2O ha−1) and two timings of application of K (single application at planting furrow and split application of 50% at planting furrow plus 50% at hilling), as potassium chloride, as well as a control (without K application) on the plant nutrition and tuber yield and quality of potato ‘Agata’ grown in tropical clay soils. The split application of K fertilizer had little influence on plant nutrition and tuber yield and quality. The influence of K fertilization on increasing K and reducing Ca and Mg concentrations in the leaf was more significant in soil with low exchangeable K. In this soil, the maximum tuber yield (33.6 Mg ha−1; 107% higher than the control) was obtained with an estimated rate of 325 kg K2O ha−1, while in the soils with medium and high exchangeable K, the tuber yield was increased between 22 and 34% and only up to a rate of 200 kg K2O ha−1. The critical leaf K concentration to reach 95% of the maximum yield was 29.3 g K kg−1, but there was an extreme increase in the tuber yield even with K rates that provided leaf K concentrations above this limit. Potassium fertilization increased the firmness and reduced soluble solids and protein in tubers. Core Ideas K is the nutrient that is most taken up and removed by the potato crop. In clay soils, the splitting of K fertilization has little influence on potato tuber yield and quality. K fertilization increases tuber yield more, and up to higher rates in soil with low K concentration. K fertilization increases the tuber firmness, but reduces the soluble solids and protein concentration.

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