Core Ideas Humic acid coatings on monoammonium phosphate had no effect on P lability or mobility. Struvite provided the lesser P mobility among the fertilizers tested. There was greater P mobility in soils with high sand content and low initial pH. The fertilizer industry has attempted to increase P mobility and lability after fertilizer application by using nonconventional phosphates or by including additives in the fertilizer formulation. We incubated granular monoammonium phosphate (MAP), sulfur‐coated MAP, humic acid‐coated MAP, triple superphosphate (TSP), ammonium potassium polyphosphate (AKPP), and ammonium magnesium phosphate (struvite) with soils from the United States and Brazil in Petri dishes for 56 d. We estimated P mobility by measuring P movement away from fertilizer granules and assessed P lability through sequential chemical fractionation of soil collected from the dishes. In addition, we monitored the change in soil pH with distance from fertilizer placed in the Petri dish. Soil pH changed in response to fertilizer additions as a function of initial soil pH. In fertilized soils, the soil pH response followed a quadratic function as the distance from the fertilizer placement site increased. Soil characteristics influenced P mobility, with mobility decreasing from the Hubbard (12% clay; pH 5.3), to Brazil (20% clay; pH 6.5), to Normania (22% clay; pH 5.5), and then Barnes (31% clay; pH 8.0) soil. The use of MAP‐based fertilizers resulted in the greatest mobility, while struvite provided the lowest mobility. In contrast, struvite granules dissolved the least resulting in the highest labile P concentrations, due to direct extraction of fertilizer P from undissolved granules (average of 73% of applied P). Comparatively, TSP provided the lowest amount of labile P (average of 52% applied P). Sulfur and humic acid‐coated MAP had no effect on P lability or mobility.

SUMMARYNitrogen fertilization is a major component of the cost of agricultural production, due to the high cost and low efficiency of fertilizers. In the case of urea, the low efficiency is mainly due to losses by volatilization, which are more pronounced in cultivation systems in which plant residues are left on the soil. The objective of this work was to compare the influence of urea coated with sulfur or boric acid and copper sulfate with conventional N fertilizers on N volatilization losses in sugar cane harvested after stubble burning. The sources urea, sulfurcoated urea, urea coated with boric acid and copper sulfate, as well as nitrate and ammonium sulfate, were tested at amounts containing N rates of 120 kg ha -1 N. The integration of new technologies in urea fertilization can reduce N losses by volatilization. These losses were most reduced when using nitrate and ammonium sulfate. The application of a readily acidified substance (boric acid) to urea was more efficient in reducing volatilization losses and nutrient removal by sugar cane than that of a substance with gradual acidification (elemental sulfur).

In Brazilian agriculture, urea is the most commonly used nitrogen (N) source, in spite of having the disadvantage of losing considerable amounts of N by ammonia-N volatilization. The objectives of this study were to evaluate: N lossby ammonia volatilization from: [urea coated with copper sulfate and boric acid], [urea coated with zeolite], [urea+ammonium sulfate], [urea coated with copper sulfate and boric acid+ammonium sulfate], [common urea] and [ammonium nitrate]; and the effect of these N source son the maize yield in terms of amount and quality. The treatments were applied to the surface of a soil under no-tillage maize, in two growing seasons. The first season (2009/2010) was after a maize crop (maize straw left on the soil surface) and the second cycle (2012/2011) after a soybean crop. Due to the weather conditions during the experiments, the volatilization of ammonia-N was highest in the first four days after application of the N sources. Of all urea sources, under volatilization-favorable conditions, the loss of ammonia from urea coated with copper sulfate and boric acid was lowest, while under high rainfall, the losses from the different urea sources was similar, i.e., an adequate rainfall was favorablet o reduce volatilization. The ammonia volatilization losses were greatest in the first four days after application. Maize grain yield differed due to N application and in the treatments, but this was only observed with cultivation of maize crop residues in 2009/2010. The combination of ammonium+urea coated with copper sulfate and boric acid optimized grain yield compared to the other urea treatments. The crude protein concentration in maize was not influenced by the technologies of urea coating.

SUMMARYA form of increasing the efficiency of N fertilizer is by coating urea with polymers to reduce ammonia volatilization. The aim of this study was to evaluate the effect of polymer-coated urea on the control of ammonia volatilization, yield and nutritional characteristics of maize. The experiment was carried out during one maize growing cycle in 2009/10 on a Geric Ferralsol, inUberlândia, MG, Brazil. Nitrogen fertilizers were applied as topdressing on the soil surface in the following urea treatments: polymer-coated urea at rates of 45, 67.5 and 90 kg ha -1 N and one control treatment (no N), in randomized blocks with four replications. Nitrogen application had a favorable effect on N concentrations in leaves and grains, Soil Plant Analysis Development (SPAD) chlorophyll meter readings and on grain yield, where as coated urea had no effect on the volatilization rates, SPAD readings and N leaf and grain concentration, nor on grain yield in comparison to conventional fertilization.Index terms: nitrogen, polymer-coated urea, N fertilizer, ammonia volatilization, Zea mays, SPAD reading.( Uma das maneiras de aumentar a eficiência dos fertilizantes nitrogenados, visando, por exemplo, à redução de perdas de amônia por volatilização, é o revestimento desses com polímeros. Objetivou-se avaliar o efeito da aplicação de ureia revestida com polímeros no controle da volatilização de amônia e a sua influência nos componentes da produção na cultura do milho. O experimento foi instalado na safra 2009/10 no município de Uberlândia, MG, em um Latossolo Vermelho-Amarelo (LVA) distrófico textura argilosa. Os tratamentos consistiram na aplicação, em cobertura no milho, de ureia revestida com polímeros e ureia convencional nas doses de 45; 67,5; e 90 kg ha -1 de N, mais um tratamento-controle (sem N), dispostos em blocos casualizados. A aplicação de N influenciou positivamente o teor do nutriente nas folhas e nos grãos, a leitura SPAD e a produtividade de grãos, porém a ureia revestida não alterou as taxas de volatilização de amônia, a leitura SPAD e o teor de N nas folhas e grãos, assim como a produtividade de grãos em relação à aplicação do fertilizante convencional.Termos de indexação: nitrogênio, ureia revestida com polímeros, fertilizante nitrogenado, volatilização de amônia, Zea mays, leitura SPAD.

SUMMARYHygroscopic fertilizers tend to absorb moisture from the air and may have undesirable characteristics such as moistness, clumping and lower fluidity, hampering the application. The increasing use of urea is due to its numerous advantages, although this nitrogen (N) source is highly susceptible to volatilization losses, particularly when applied to the soil surface of management systems with conservation of crop residues. The volatilization losses can be minimized by slow or controlled-release fertilizers, with controlled water solubility of the urea-coating materials; and by stabilized fertilizers, which prolong the period during which N remains in the amide or ammonia forms by urease inhibitors. This study evaluated the hygroscopicity of and ammonia volatilization from urea coated with boric acid and copper sulfate or with sulfur. The hygroscopicity of the sources was evaluated over time after exposure to five levels of relative humidity (RH) and volatilization evaluated after application to the soil surface covered with sugarcane trash. Ammonium nitrate has a low potential for volatilization losses, but is highly hygroscopic. Although coating with boric acid and copper sulfate or elemental sulfur reduced the critical humidity level of urea, the delay in the volatilization process is a potential positive factor.Index terms: boric acid, sulfur, crop residues, copper sulphate. Fertilizantes higroscópicos tendem a absorver a umidade do ar e podem apresentar características indesejáveis como mela, empedramento, menor fluidez, em que a consequência é a difícil aplicação. O crescente uso de ureia é atribuído às suas inúmeras vantagens, porém essa fonte apresenta elevada susceptibilidade a perdas por volatilização de amônia, principalmente quando aplicada em superfície em sistemas com conservação da palhada. Para minimizar esse tipo de perda, existem os fertilizantes de liberação lenta ou controlada pelo controle de solubilidade em água de materiais utilizados no revestimento da ureia; e os estabilizados, que prolongam o tempo em que o N permanece nas formas amídica ou amoniacal por meio de inibidores de urease. Objetivou-se, neste trabalho, avaliar a higroscopicidade e as perdas por volatilização de amônia da ureia revestida com ácido bórico e sulfato de cobre e ureia revestida com enxofre. A higroscopicidade das fontes foi avaliada ao longo do tempo, após a exposição a cinco níveis de umidade relativa do ar; e a volatilização avaliada, após aplicação em superfície na palhada da cana. O nitrato de amônio apresentou baixo potencial de perdas por volatilização, porém teve elevada higroscopicidade. O revestimento com acido bórico e sulfato de cobre ou com enxofre elementar reduziu o ponto de umidade crítico da ureia, porém apresentou como um dos fatores positivos o potencial em retardar o processo de volatilização.Termos de indexação: ácido bórico, enxofre, palhada, sulfato de cobre.

Superação de dormência e qualidade da luz na germinação de sementes de chamaecrhysta rotundifolia (Pers.) Greene Overcoming dormancy and light quality in the Germination of seeds of chamaecrhysta rotundifolia (Pers.

Soils are characterized by high phosphorus (P) immobilization, considering the major limiting factor for agricultural production in Brazil. Phosphate fertilizers complexed with humic acids (HA) have been presented as an alternative to inhibit P immobilization in soils; however, little is known regarding its efficiency or its effect on soil P dynamics when associated with liming. The objective was to investigate labile moderately and non-labile P changes in sandy and clayey soils under application of distinct P sources and liming. Tropical soils were incubated using 200 mg kg −1 of P (simple superphosphate-SSP and SSP + HA), associated or not with calcium oxide. Check-plots were run in both soils without any P addition and/or no liming. After 60, 90, and 180 days of incubation, P contents were fractionated into P inorganic (Pi) and organic (Po), in the following pools: labile (P AER and P BIC), moderately labile (P HCl and P HID-0.1), and non-labile fractions (P HID-0.5 and P residual). There was a P flux between non-labile and labile fractions, controlled by the use of P fertilizer and liming. In sandy soil, the P addition promoted a clear P flux from non-labile to labile fractions; however, in clayey soil, there was a reverse P flux. The lack of P addition promotes a negative balance in soil with a decrease of labile fractions, mainly when associated with liming. Therefore, inputs are necessary to avoid soil P depletion.

Selenium (Se) fertilisation in grazing systems can improve the quality of animal forage, but there are few studies addressing the influence of Se fertilisation on the chemical composition and ruminal degradability of forage fertilised with Se. The aim of this study was to evaluate the chemical composition and in vitro assays of truly degraded organic matter (TDOM), short-chain fatty acids (SCFA) total gas (GP) and methane (CH ) production of two harvests of Brachiaria brizantha cv. Marandu fertilised with urea coated with B, Cu and sodium selenate for 0, 10, 20, 40, 80 and 160 g/ha of Se. Selenium content in forage increased linearly with the different doses at 30 and 60 days after fertilisation. However, doses of 20 and 80 g/ha Se fertilisation yielded positive effects increasing Se content and truly degraded organic matter in vitro of Brachiaria brizantha cv. Marandu.