reSUmOO estado do paraná não dispõe de um sistema de recomendação de adubação para rotação de culturas em plantio direto (pD). em razão disso, utiliza indicações geradas para culturas individuais há mais de 30 anos e em preparo convencional. este estudo teve como objetivo consolidar a calibração de p e avaliar a resposta das culturas à adubação fosfatada, visando à proposição de um sistema de indicações técnicas para a adubação fosfatada das culturas da soja, do milho, do trigo e da cevada cultivadas em sistema de rotação em latossolos com longo histórico de pD (>30 anos) na região centro-sul do paraná, que se caracteriza por possuir alto potencial produtivo. três experimentos de calibração foram conduzidos de 2008 a 2013 e consistiram na criação de níveis de p pela aplicação de doses a lanço de até 640 kg ha -1 de p 2 O 5 . Quarenta e quatro experimentos de resposta a p foram conduzidos entre as safras de 2011 a 2012/13, tendo como foco avaliar a resposta das culturas a p em solos com distinta disponibilidade do nutriente. Os rendimentos relativos [rr = (rendimento sem p/rendimento máximo) × 100] das culturas e os teores de p no solo (mehlich-1) foram relacionados, obtendo-se os teores críticos e as classes de disponibilidade de p no solo. para a estimativa das doses nas classes de disponibilidade baixa e Média, foram utilizadas as curvas de resposta à adubação de P, seguindo a filosofia de suficiência Recebido para publicação em 29 de julho de 2014 e aprovado em 12 de janeiro de 2015.

nitrogen losses by ammonia (nH 3 ) volatilization can be reduced by appropriate irrigation management or by alternative n sources, replacing urea. the objective of this study was to evaluate the efficiency of irrigation management and N source combinations in decreasing NH 3 volatilization from an Argissolo Vermelho Distrófico típico cultivated for 28 years with black oat (Avena strigosa) and maize (Zea mays), under no-tillage in the region of depressão central, rio grande do sul, Brazil. the experiment was arranged in a randomized block design with split plots with three replications, where the main plots consisted of irrigation systems: no irrigation; irrigation immediately before and irrigation immediately after fertilization. the subplots were treated with different n sources: urea, urea with urease inhibitor and slow-release fertilizer, at an n rate of 180 kg ha -1 , broadcast over maize, plus a control treatment without n fertilization. ammonia volatilization was assessed using semi-open static collectors for 1, 2, 4, 6, and 10 days after n fertilization. In general, more than 90 % of total nH 3 -n losses occurred until three days after n fertilization, with peaks up to 15.4 kg ha -1 d -1. The irrigation was efficient to reduce NH 3 losses only when applied after n fertilization. However, reductions varied according to the n fertilizer, and were higher for urea (67 %) and slightly lower for urea with urease inhibitor (50 %) and slow-release fertilizer (40 %), compared with the mean of the treatments without irrigation and irrigation before fertilization. the use of urea with urease inhibitor instead of urea was only promising under volatilization-favorable conditions (no irrigation or irrigation before n fertilization). compared to urea, slow-release fertilizer did not reduce ammonia volatilization in any of the rainfed or irrigated treatments.

Fertilization programs for annual crops in the state of Paraná, southern Brazil, are based on studies that focused on conventional tillage and were established more than 30 years ago. The primary purpose of this study was to assess potassium (K) fertilization on long-term (>30 years) no-tillage soybean, corn, wheat, and barley crops grown in rotation on Oxisols in the central-southern region of Paraná. A total of 47 experiments were carried out from 2008 to 2013, three of which addressed K calibration and the other 44, crop response to K fertilization. Critical K soil-test value and interpretation classes were established from the ratio between relative crop yield [RY = (yield without K/max yield) × 100] and soil K levels. Winter cereals were found to be more demanding of K than were soybean and corn; also, the former governed critical K soil-test value for crop rotation: 0.23 cmol c dm -3 in the 0.00-0.20 m soil layer. Recommended fertilization rates for soils in the low and medium soil K levels were established by using the build-up approach for soil correction; and those for the high and very high soil K levels were established by removing K at harvest and assessing economic return in crop response experiments. The K rates calculated for the high yield classes exceeded those currently recommended for use in Paraná.

High nitrogen (N) losses by ammonia (NH 3 ) volatilization from urea can compromise nitrogen fertilization efficiency and corn yield. The purpose of this study was to assess the effects of irrigation management and the addition of the urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT) on NH 3 -N losses from urea and on corn yield. To this end, two experiments were carried out in the 2011/12 crop season on a sandy clay loam Acrisol in the Central Basin region of Rio Grande do Sul, southern Brazil. Experiment I consisted of two different N sources (urea and urea plus the inhibitor) at a rate of 200 kg ha -1 N and two corn sowing times [viz., an early time (Sept. 3, 2011) and an intermediate time (Oct. 3, 2011)]. Experiment II considered a combination of three irrigation management systems (viz., without irrigation on the fertilization day and on the next 7 days; 20 mm of water immediately before N fertilization; and 20 mm water after N fertilization) and two N sources (urea and urea plus the inhibitor) at 150 kg ha -1 N. A control treatment without topdressed N fertilization was also performed in parallel with the two experiments. The NH 3 -N losses from common urea increased with increasing soil moisture in Experiment I (25 % applied N), and with irrigation before N fertilization in Experiment II (27 % applied N). The inhibitor reduced NH 3 -N losses from urea by 46 to 80 %. Also, irrigation after fertilization reduced ammonia volatilization by 83 % on average, with little effect from the inhibitor. The effects of the inhibitor and post-fertilization irrigation on the mitigation of NH 3 losses by volatilization from urea were not additive; in addition, they led to no increase in corn yield.

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