Fertilizer 15N balance in a coffee cropping system: a case study in Brazil

Knowledge about the fate of fertilizer nitrogen in agricultural systems is essential for the improvement of management practices in order to maximize nitrogen (N) recovery by the crop and reduce N losses from the system to a minimum. This study involves fertilizer management practices using the 15N isotope label applied in a single rate to determine the fertilizer-N balance in a particular soil-coffee-atmosphere system and to deepen the understanding of N plant dynamics. Five replicates consisting of plots of about 120 plants each were randomly defined within a 0.2 ha coffee plantation planted in 2001, in Piracicaba, SP, Brazil. Nine plants of each plot were separated in sub-plots for the 15N balance studies and treated with N rates of 280 and 350 kg ha-1 during 2003/2004 and 2004/2005, respectively, both of them as ammonium sulfate enriched to a 15N abundance of 2.072 atom %. Plant shoots were considered as separate parts: the orthotropic central branch, productive branches, leaves of productive branches, vegetative branches, leaves of vegetative branches and fruit. Litter, consisting of dead leaves accumulated below the plant canopy, was measured by the difference between leaves at harvest and at the beginning of the following flowering. Roots and soil were sampled down to a depth of 1.0 at intervals of 0.2 m. Samples from the isotopic sub-plots were used to evaluate total N and 15N, and plants outside sub-plots were used to evaluate dry matter. Volatilization losses of NH3 were estimated using special collectors. Leaching of fertilizer-N was estimated from deep drainage water fluxes and 15N concentrations of the soil solution at 1 m soil depth. At the end of the 2-year evaluation, the recovery of 15N applied as ammonium sulfate was 19.1 % in aerial plant parts, 9.4 % in the roots, 23.8 % in the litter, 26.3 % in the fruit and 12.6 % remaining in the 0_1.0 m soil profile. Annual leaching and volatilization losses were very small (2.0 % and 0.9 %, respectively). After two years, only 6.2 % N were missing in the balance (100 %) which can be attributed to other non-estimated compartments and experimental errors. Results show that an enrichment of only 2 % atom 15N allows the study of the partition of fertilizer-N in a perennial crop such as coffee during a period of two years.

Effect of fertilizer-N application and seed coating with rhizobial inoculants on soybean yield in eastern Paraguay

Nitrogen removal in soybean grains at harvest may exceed biological N2 fixation, particularly if grain yields are as high as typically achieved on "Terra Rossa" soils of Eastern Paraguay. Applying N fertilizer or coating seeds with rhizobial inoculants that enhance nodulation may represent a way of balancing the N budget. However, the effects of such treatments appear to be highly site-specific. The objective of this study was to examine the effects of N application (N) and rhizobial inoculation (I) on nodulation, N accumulation and soybean yields in Eastern Paraguay. Field experiments were conducted in two consecutive soybean seasons. Dry conditions in the first year delayed sowing and reduced plant number m-2 and pod number plant-1. Grain yields were generally below 2 t ha-1 but the +N+I treatment increased yields by about 75%. In the second year favorable conditions resulted in yields of around 4 t ha-1 and the treatments had no effect. Nitrogen accumulation was higher in the first year and could therefore not explain the observed yield differences between years and treatment combinations. The positive effect of the +N+I treatment in year one was associated with a more rapid root growth which could have reduced susceptibility to intermittent drought stress. Nodule biomass decreased between flowering and pod setting stages in the +I treatment whereas further increases in nodule biomass in the -I treatment may have led to competition for assimilates between nodules and developing pods. Based on these preliminary results we conclude that N application and seed inoculation can offer short-term benefits in unfavorable years without negative effects on yield in favorable years.

Phosphorus and root distribution and corn growth as related to long-term tillage systems and fertilizer placement

Soil and fertilizer management during cultivation can affect crop productivity and profitability. Long-term experiments are therefore necessary to determine the dynamics of nutrient and root distribution as related to soil profile, as well as the effects on nutrient uptake and crop growth. An 18-year experiment was conducted at the Federal University of Rio Grande do Sul State (UFRGS), in Eldorado do Sul, Brazil, on Rhodic Paleudult soil. Black oat and vetch were planted in the winter and corn in the summer. The soil management methods were conventional, involving no-tillage and strip tillage techniques and broadcast, row-and strip-applied fertilizer placement (triple superphosphate). Available P (Mehlich-1) and root distribution were determined in soil monoliths during the corn grain filling period. Corn shoot dry matter production and P accumulation during the 2006/2007 growing season were determined and the efficiency of P utilization calculated. Regardless of the degree of soil mobilization, P and roots were accumulated in the fertilized zone with time, mainly in the surface layer (0-10 cm). Root distribution followed P distribution for all tillage systems and fertilizer treatments. Under no-tillage, independent of the fertilizer placement, the corn plants developed more roots than in the other tillage systems. Although soil tillage systems and fertilizer treatments affected P and root distribution throughout the soil profile, as well as P absorption and corn growth, the efficiency of P utilization was not affected.

15N uptake fom manure and fertilizer sources by three consecutive crops under controlled conditions

There are several regions of the world where soil N analysis and/or N budgets are not used to determine how much N to apply, resulting in higher than needed N inputs, especially when manure is used. One such region is the North Central "La Comarca Lagunera", one of the most important dairy production areas of Mexico. We conducted a unique controlled greenhouse study using 15N fertilizer and 15N isotopic-labeled manure that was labeled under local conditions to monitor N cycling and recovery under higher N inputs. The manure-N treatment was applied only once and was incorporated in the soil before planting the first forage crop at an equivalent rate of 30, 60 and 120 Mg ha-1 dry manure. The 15N treatments were equivalent to 120 and 240 kg ha-1 (NH4)2SO4-N for each crop. The total N fertilizer for each N fertilized treatment were 360, and 720 kg ha-1 N. We found very low N recoveries: about 9 % from the manure N inputs, lower than the 22 to 25 % from the fertilizer N inputs. The manure N recovered belowground in soil and roots ranged from 82 to 88 %. The low recoveries of N by the aboveground and low soil inorganic nitrate (NO3-N) and ammonium (NH4-N) content after the third harvested suggested that most of the 15N recovered belowground was in the soil organic form. The losses from manure N inputs ranged from 3 to 11 %, lower than the 34 to 39 % lost from fertilizer N sources. Our study shows that excessive applications of manure or fertilizer N that are traditionally used in this region will not increase the rate of N uptake by aboveground compartment but will increase the potential for N losses to the environment.

Utilization of Boron (10B) derived from fertilizer by sugar cane

The response to B in agricultural systems of sugar cane is still an unexplored issue; B application has however recently been widely publicized and used with a certain degree of frequency. The use of 10B-labeled fertilizers may further contribute to clarify this practice. With the objective of evaluating sugar cane use of B (10B) derived from fertilizer (boric acid), an experiment was conducted under field conditions in the 2005/2006 growing season. The experiment consisted of the installation of microplots (2 x 1.5 m) where 4 kg ha-1 B (boric acid with 85.95 % in 10B atoms) dissolved in water was applied 90 days after planting (May 2005). The solution was applied to the soil on both sides of the plant row at a distance of 20 cm. After harvest (June 2006) the B content and 10B abundance in % atoms in all parts of the sugar cane plants (stalks, dry leaves, tips and roots) were determined. Results showed that the total B accumulated was 471 g ha-1 in the entire plant (35 % in the stalks, 22 % in the dry leaves, 9 % in the tips and 34 % in the roots). The sugar cane plants used on average 14 % of the total accumulated B in the above-ground part (44 g ha-1) and 11 % in the roots (19 g ha-1), totaling 13 % in the entire plant (63 g ha-1). The recovery of 10B-fertilizer by sugar cane plants was low, around 2 % of the total applied amount.

Nitrous oxide and methane fluxes in south Brazilian gleysol as affected by nitrogen fertilizers

Nitrogen fertilizers increase the nitrous oxide (N2O) emission and can reduce the methane (CH4) oxidation from agricultural soils. However, the magnitude of this effect is unknown in Southern Brazilian edaphoclimatic conditions, as well as the potential of different sources of mineral N fertilizers in such an effect. The aim of this study was to investigate the effects of different mineral N sources (urea, ammonium sulphate, calcium nitrate, ammonium nitrate, Uran, controlled- release N fertilizer, and urea with urease inhibitor) on N2O and CH4 fluxes from Gleysol in the South of Brazil (Porto Alegre, RS), in comparison to a control treatment without a N application. The experiment was arranged in a randomized block with three replications, and the N fertilizer was applied to corn at the V5 growth stage. Air samples were collected from a static chambers for 15 days after the N application and the N2O and CH4 concentration were determined by gas chromatography. The topmost emissions occurred three days after the N fertilizer application and ranged from 187.8 to 8587.4 µg m-2 h-1 N. The greatest emissions were observed for N-nitric based fertilizers, while N sources with a urease inhibitor and controlled release N presented the smallest values and the N-ammonium and amidic were intermediate. This peak of N2O emissions was related to soil NO3--N (R² = 0.56, p < 0.08) when the soil water-filled pore space was up to 70 % and it indicated that N2O was predominantly produced by a denitrification process in the soil. Soil CH4 fluxes ranged from -30.1 µg m-2 h-1 C (absorption) to +32.5 µg m-2 h-1 C (emission), and the accumulated emission in the period was related to the soil NH4+-N concentration (R² = 0.82, p < 0.001), probably due to enzymatic competition between nitrification and metanotrophy processes. Despite both of the gas fluxes being affected by N fertilizers, in the average of the treatments, the impact on CH4 emission (0.2 kg ha-1 equivalent CO2-C ) was a hundredfold minor than for N2O (132.8 kg ha-1 equivalent CO2-C). Accounting for the N2O and CH4 emissions plus energetic costs of N fertilizers of 1.3 kg CO2-C kg-1 N regarding the manufacture, transport and application, we estimated an environmental impact of N sources ranging from 220.4 to 664.5 kg ha-1 CO2 -C , which can only be partially offset by C sequestration in the soil, as no study in South Brazil reported an annual net soil C accumulation rate larger than 160 kg ha-1 C due to N fertilization. The N2O mitigation can be obtained by the replacement of N-nitric sources by ammonium and amidic fertilizers. Controlled release N fertilizers and urea with urease inhibitor are also potential alternatives to N2O emission mitigation to atmospheric and systematic studies are necessary to quantify their potential in Brazilian agroecosystems.

Ammonia volatilization in no-till system in the south-central region of the State of Paraná, Brazil

Ammonia (NH3) volatilization can reduce the efficiency of urea applied to the surface of no-till (NT) soils. Thus, the objectives of this study were to evaluate the magnitude of NH3 losses from surface-applied urea and to determine if this loss justifies the urea incorporation in soil or its substitution for other N sources under the subtropical climatic conditions of South-Central region of Paraná State, Brazil. The experiment, performed over four harvesting seasons in a clayey Hapludox followed a randomized block design with four replicates. A single dose of N (150 kg ha-1) to V5 growth stage of corn cultivated under NT system was applied and seven treatments were evaluated, including surface-applied urea, ammonium sulfate, ammonium nitrate, urea with urease inhibitor, controlled-release N source, a liquid N source, incorporated urea, and a control treatment with no N application. Ammonia volatilization was evaluated for 20 days after N application using a semi-open static system. The average cumulative NH3 loss due to the superficial application of urea was low (12.5 % of the applied N) compared to the losses observed in warmer regions of Southeastern Brazil (greater than 50 %). The greatest NH3 losses were observed in dry years (up to 25.4 % of the applied N), and losses decreased exponentially as the amount of rainfall after N application increased. Incorporated urea and alternative N sources, with the exception of controlled-release N source, decreased NH3 volatilization in comparison with surface-applied urea. Urea incorporation is advantageous for the reduction of NH3 volatilization; however, other aspects as its low operating efficiency should be considered before this practice is adopted. In the South-Central region of Paraná, the low NH3 losses from the surface-applied urea in NT system due to wet springs and mild temperatures do not justify its replacement for other N sources.

Nitrogen washing from C3 and C4 cover grasses residues by rain

Crop species with the C4 photosynthetic pathway are more efficient in assimilating N than C3 plants, which results in different N amounts prone to be washed from its straw by rain water. Such differences may affect N recycling in agricultural systems where these species are grown as cover crops. In this experiment, phytomass production and N leaching from the straw of grasses with different photosynthetic pathways were studied in response to N application. Pearl millet (Pennisetum glaucum) and congo grass (Brachiaria ruziziensis) with the C4 photosynthetic pathway, and black oat (Avena Strigosa) and triticale (X Triticosecale), with the C3 photosynthetic pathway, were grown for 47 days. After determining dry matter yields and N and C contents, a 30 mm rainfall was simulated over 8 t ha-1 of dry matter of each plant residue and the leached amounts of ammonium and nitrate were determined. C4 grasses responded to higher fertilizer rates, whereas N contents in plant tissue were lower. The amount of N leached from C4 grass residues was lower, probably because the C/N ratio is higher and N is more tightly bound to organic compounds. When planning a crop rotation system it is important to take into account the difference in N release of different plant residues which may affect N nutrition of the subsequent crop.

Decomposition and nutrient release of leguminous plants in coffee agroforestry systems

Leguminous plants used as green manure are an important nutrient source for coffee plantations, especially for soils with low nutrient levels. Field experiments were conducted in the Zona da Mata of Minas Gerais State, Brazil to evaluate the decomposition and nutrient release rates of four leguminous species used as green manures (Arachis pintoi, Calopogonium mucunoides, Stizolobium aterrimum and Stylosanthes guianensis) in a coffee agroforestry system under two different climate conditions. The initial N contents in plant residues varied from 25.7 to 37.0 g kg-1 and P from 2.4 to 3.0 g kg-1. The lignin/N, lignin/polyphenol and (lignin+polyphenol)/N ratios were low in all residues studied. Mass loss rates were highest in the first 15 days, when 25 % of the residues were decomposed. From 15 to 30 days, the decomposition rate decreased on both farms. On the farm in Pedra Dourada (PD), the decomposition constant k increased in the order C. mucunoides < S. aterrimum < S. guianensis < A. pintoi. On the farm in Araponga (ARA), there was no difference in the decomposition rate among leguminous plants. The N release rates varied from 0.0036 to 0.0096 d-1. Around 32 % of the total N content in the plant material was released in the first 15 days. In ARA, the N concentration in the S. aterrimum residues was always significantly higher than in the other residues. At the end of 360 days, the N released was 78 % in ARA and 89 % in PD of the initial content. Phosphorus was the most rapidly released nutrient (k values from 0.0165 to 0.0394 d-1). Residue decomposition and nutrient release did not correlate with initial residue chemistry and biochemistry, but differences in climatic conditions between the two study sites modified the decomposition rate constants.

Attributes of irrigated rice as affected by soil sodicity and potassic fertilizer application

Soils of the coastal plains of Rio Grande do Sul, Brazil, are affected by salinization, which can hamper the establishment and development of crops in general, including rice. The application of high doses of KCl may aggravate the crop damage, due to the high saline content of this fertilizer. This study aimed to evaluate the effect of K fertilizer management on some properties of rice plant, grown in soils with different sodicity levels, and determine which attribute is best related to yield. The field study was conducted in four Albaqualfs with exchangeable Na percentages of 5.6, 9.0, 21 and 32 %. The management of KCl fertilizer consisted of the application of 90 kg ha-1 K2O broadcast, 90 kg ha-1 K2O in the row and 45 kg ha-1 K2O in the row + 45 kg ha-1 K2O at panicle initiation (PI). Plant density, dry matter evolution, height, SPAD (Soil Plant Analysis Development value indicating relative chlorophyll contents) index, tiller mass, 1,000-grain weight, panicle length and grain yield were evaluated. The plant density was damaged by application of K fertilizer in the row, especially at full dose (90 kg ha-1), at three sodicity levels, resulting in loss in biomass accumulation in later stages, affecting the crop yield, even at the lowest level of soil sodicity (5.6 %). All properties were correlated with yield; the highest positive correlation was found with plant density and shoot dry matter at full flowering, and a negative correlation with panicle length.

Nitrogen fertilizer use efficiency, recovery and leaching of an alexandergrass pasture

Nitrogen usually determines the productive potential of forage crops, although it is highly unstable in the environment. Studies on recovery rates and use efficiency are important for more reliable fertilizer recommendations to reduce costs and avoid environmental pollution. The purpose of this study was to evaluate N use efficiency and recovery rate of Alexandergrass pasture (Brachiaria - Syn. Urochloa plantaginea) as well as N-NO3- and N-NH4+ soil concentrations using different levels of N fertilization under two grazing intensities. The experiment was arranged in a randomized block design in a factorial scheme with three replications. Treatments consisted of three N rates (0, 200 and 400 kg ha-1 N) and two grazing intensities termed low mass (LM; forage mass of 2,000 kg ha-1 of DM) and high mass (HM; forage mass of 3,600 kg ha-1 of DM) under continuous stocking and variable stocking rates. Results of N fertilization with 200 kg ha-1 were better than with 400 kg ha-1 N. There was a significant effect of N rates on soil N-NO3-concentration with higher levels in the first layer of the soil profile in the treatment with 400 kg ha-1 N. Grazing intensity also affected soil N-NO3- concentration, by increasing the levels under the higher stocking rate (lower forage mass).

Extractants to assess zinc phytoavailability in mineral fertilizer and industrial by-products

Efficient analytical methods for the quantification of plant-available Zn contained in mineral fertilizers and industrial by-products are fundamental for the control and marketing of these inputs. In this sense, there are some doubts on the part of the scientific community as well as of the fertilizer production sector, whether the extractor requested by the government (Normative Instruction No. 28, called 2nd extractor), which is citric acid 2 % (2 % CA) (Brasil, 2007b), is effective in predicting the plant availability of Zn via mineral fertilizers and about the agronomic significance of the required minimal solubility of 60 % compared to the total content (HCl) (Brasil, 2007a). The purpose of this study was to evaluate the alternative extractors DTPA, EDTA, neutral ammonium citrate (NAC), buffer solution pH 6.0, 10 % HCl, 10 % sulfuric acid, 1 % acetic acid, water, and hot water to quantify the contents of Zn available for maize and compare them with indices of agronomic efficiency of fertilizers and industrial by-products when applied to dystrophic Clayey Red Latosol and Dystrophic Alic Red Yellow Latosol with medium texture. The rate of Zn applied to the soil was 5 mg kg-1, using the sources zinc sulfate, commercial granular zinc, ash and galvanic sludge, ash and two brass slags. Most Zn was extracted from the sources by DTPA, 10 % HCl, NAC, 1% acetic acid, and 10 % sulfuric acid. Recovery by the extractors 2 % CA, EDTA, water, and hot water was low. The agronomic efficiency index was found to be high when using galvanic sludge (238 %) and commercial granular zinc (142 %) and lower with brass slag I and II (67 and 27 %, respectively). The sources galvanizing ash and brass ash showed solubility lower than 60 % in 2 % CA, despite agronomic efficiency indices of 78 and 125 %, respectively. The low agronomic efficiency index of industrial by-products such as brass slag I and galvanizing ash can be compensated by higher doses, provided there is no restriction, as well as for all other sources, in terms of contaminant levels of arsenic, cadmium, chromium, lead, and mercury as required by law (Normative Instruction No 27/2006). The implementation of 2nd extractor 2 % CA and the requirement of minimum solubility for industrial by-products could restrict the use of alternative sources as potential Zn sources for plants.

Optical crop sensor for variable-rate nitrogen fertilization in corn: II - indices of fertilizer efficiency and corn yield

Generally, in tropical and subtropical agroecosystems, the efficiency of nitrogen (N) fertilization is low, inducing a temporal variability of crop yield, economic losses, and environmental impacts. Variable-rate N fertilization (VRF), based on optical spectrometry crop sensors, could increase the N use efficiency (NUE). The objective of this study was to evaluate the corn grain yield and N fertilization efficiency under VRF determined by an optical sensor in comparison to the traditional single-application N fertilization (TSF). With this purpose, three experiments with no-tillage corn were carried out in the 2008/09 and 2010/11 growing seasons on a Hapludox in South Brazil, in a completely randomized design, at three different sites that were analyzed separately. The following crop properties were evaluated: aboveground dry matter production and quantity of N uptake at corn flowering, grain yield, and vegetation index determined by an N-Sensor® ALS optical sensor. Across the sites, the corn N fertilizer had a positive effect on corn N uptake, resulting in increased corn dry matter and grain yield. However, N fertilization induced lower increases of corn grain yield at site 2, where there was a severe drought during the growing period. The VRF defined by the optical crop sensor increased the apparent N recovery (NRE) and agronomic efficiency of N (NAE) compared to the traditional fertilizer strategy. In the average of sites 1 and 3, which were not affected by drought, VRF promoted an increase of 28.0 and 41.3 % in NAE and NRE, respectively. Despite these results, no increases in corn grain yield were observed by the use of VRF compared to TSF.

Efficiency of nitrogen fertilizer applied at corn sowing in contrasting growing seasons in Paraguay

In order to select soil management practices that increase the nitrogen-use efficiency (NUE) in agro-ecosystems, the different indices of agronomic fertilizer efficiency must be evaluated under varied weather conditions. This study assessed the NUE indices in no-till corn in southern Paraguay. Nitrogen fertilizer rates from 0 to 180 kg ha-1 were applied in a single application at corn sowing and the crop response investigated in two growing seasons (2010 and 2011). The experimental design was a randomized block with three replications. Based on the data of grain yield, dry matter, and N uptake, the following fertilizer indices were assessed: agronomic N-use efficiency (ANE), apparent N recovery efficiency (NRE), N physiological efficiency (NPE), partial factor productivity (PFP), and partial nutrient balance (PNB). The weather conditions varied largely during the experimental period; the rainfall distribution was favorable for crop growth in the first season and unfavorable in the second. The PFP and ANE indices, as expected, decreased with increasing N fertilizer rates. A general analysis of the N fertilizer indices in the first season showed that the maximum rate (180 kg ha-1) obtained the highest corn yield and also optimized the efficiency of NPE, NRE and ANE. In the second season, under water stress, the most efficient N fertilizer rate (60 kg ha-1) was three times lower than in the first season, indicating a strong influence of weather conditions on NUE. Considering that weather instability is typical for southern Paraguay, anticipated full N fertilization at corn sowing is not recommended due the temporal variability of the optimum N fertilizer rate needed to achieve high ANE.

Hygroscopicity and ammonia volatilization losses from nitrogen sources in coated urea

Hygroscopic 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.