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.

Sequential fractionation has helped improving our understanding of the lability and bioavailability of P in soil. Nevertheless, there have been no reports on how manipulation of the different fractions prior to analyses affects the total P (TP) concentrations measured. This study investigated the effects of sample digestion, filtration, and acidification on the TP concentrations determined by ICP-OES in 20 soil samples. Total P in extracts were either determined without digestion by ICP-OES, or ICP-OES following block digestion, or autoclave digestion. The effects of sample filtration, and acidification on undigested alkaline extracts prior to ICP-OES were also evaluated. Results showed that, TP concentrations were greatest in the block-digested extracts, though the variability introduced by the block-digestion was the highest. Acidification of NaHCO3 extracts resulted in lower TP concentrations, while acidification of NaOH randomly increased or decreased TP concentrations. The precision observed with ICP-OES of undigested extracts suggests this should be the preferred method for TP determination in sequentially extracted samples. Thus, observations reported in this work would be helpful in appropriate sample handling for P determination, thereby improving the precision of P determination. The results are also useful for literature data comparison and discussion when there are differences in sample treatments.

Sugarcane (Saccharum spp) crop has high social, economic and environmental importance for several regions throughout the world. However, the increasing demand for efficiency and optimization of agricultural resources generates uncertainties regarding high mineral fertilizer consumption. Thereby, organomineral fertilizers are to reduce the conventional sources consumption. Thus, this study was carried out to evaluate the agronomic and economic sugarcane performancies and the residual effect of p and K under mineral and organomineral fertilization. Growth and technological parameters, leaf and soil nutrients concentration in surface and subsurface layers were analyzed from sugarcane planting (plant cane) until the first ratoon. Agronomic and economic sugarcane efficiency were evaluated. At the first ratoon, resin-extractable P provided by mineral and organomineral fertilizers were, respectively, 15 and 11 mg kg −1 in the 0.0-0.2 m, and 28 and 31 mg kg −1 in 0.2-0.4 m layer. However, exchangeable K in the 0.0-0.2 m layer was 1.88 and 1.58 mmol c kg −1 for mineral and organomineral fertilizers, respectively. The yield gains over the control reached with mineral and organomineral fertilizers were, respectively, 10.99 and 17 Mg ha −1 at the lowest fertilizer rate; and 29.25 and 61.3 Mg ha −1 at the highest fertilizer rate. Agronomic and economic organomineral fertilizer efficiencies are more pronounced in plant cane. Summing two harvests, the organomineral is 7% more profitable than mineral fertilizer.