Nitrogen application timing and soil inorganic nitrogen dynamics under no-till oat/maize sequential cropping

The timing of N application to maize is a key factor to be considered in no-till oat/maize sequential cropping. This study aimed to evaluate the influence of pre-planting, planting and sidedress N application on oat residue decomposition, on soil N immobilisation and remineralisation and on N uptake by maize plants in no-till oat/maize sequential cropping. Undisturbed soil cores of 10 and 20 cm diameter were collected from the 0-15 cm layer of a no-till Red Latossol, when the oat cover crop was in the milk-grain stage. Two greenhouse experiments were conducted simultaneously. Experiment A, established in the 10 cm diameter cores and without plant cultivation, was used to asses N dynamics in soil and oat residues. Experiment B, established in the 20 cm diameter cores and with maize cultivation, was used to assess plant growth and N uptake. An amount of 6.0 Mg ha-1 dry matter of oat residues was spread on the surface of the cores. A rate of 90 kg N ha-1 applied as ammonium sulphate in both experiments was split in pre-planting, planting and sidedress applications as follows: (a) 00-00-00 (control), (b) 90-00-00 (pre-planting application, 20 days before planting), (c) 00-90-00 (planting application), (d) 00-30-60 (split in a planting and a sidedress application 31 days after emergence), (e) 00-00-00* (control, without oat residue) and (f) 90-00-00* (pre-planting application, without oat residue). The N concentration and N content in oat residues were not affected during decomposition by N fertilisation. Most of the fertiliser NH4+-N was converted into NO3--N within 20 days after application. A significant decrease in NO3--N contents in the 0-4 cm layer was observed in all treatments between 40 and 60 days after the oat residue placement on the soil surface, suggesting the occurrence of N immobilisation in this period. Considering that most of the inorganic N was converted into NO3- and that no immobilisation of the pre planting fertiliser N occurred at the time of its application, it was possible to conclude that pre-planting applied N was prone to losses by leaching. On the other hand, with split N applications, maize plants showed N deficiency symptoms before sidedress application. Two indications for fertiliser-N management in no-till oat/maize sequential cropping could be suggested: (a) in case of split application, the sidedress should be earlier than 30 days after emergence, and (b) if integral application is preferred to save field operations, this should be done at planting.

Coffee leaf and stem anatomy under boron deficiency

Boron deficiency in coffee is widely spread in Brazilian plantations, but responses to B fertilizer have been erratic, depending on the year, form and time of application and B source. A better understanding of the effects of B on plant physiology and anatomy is important to establish a rational fertilization program since B translocation within the plant may be affected by plant anatomy. In this experiment, coffee plantlets of two varieties were grown in nutrient solutions with B levels of 0.0 (deficient), 5.0 µM (adequate) and 25.0 µM (high). At the first symptoms of deficiency, leaves were evaluated, the cell walls separated and assessed for B and Ca concentrations. Scanning electron micrographs were taken of cuts of young leaves and branch tips. The response of both coffee varieties to B was similar and toxicity symptoms were not observed. Boron concentrations in the cell walls increased with B solution while Ca concentrations were unaffected. The Ca/B ratio decreased with the increase of B in the nutrient solution. In deficiency of B, vascular tissues were disorganized and xylem walls thinner. B-deficient leaves had fewer and deformed stomata.

Spatial variability of the chemical, physical and biological properties in lowland cultivated with irrigated rice

In the areas where irrigated rice is grown in the south of Brazil, few studies have been carried out to investigate the spatial variability structure of soil properties and to establish new forms of soil management as well as determine soil corrective and fertilizer applications. In this sense, this study had the objective of evaluating the spatial variability of chemical, physical and biological soil properties in a lowland area under irrigated rice cultivation in the conventional till system. For this purpose, a 10 x 10 m grid of 100 points was established, in an experimental field of the Embrapa Clima Temperado, in the County of Capão do Leão, State of Rio Grande do Sul. The spatial variability structure was evaluated by geostatistical tools and the number of subsamples required to represent each soil property in future studies was calculated using classical statistics. Results showed that the spatial variability structure of sand, silt, SMP index, cation exchange capacity (pH 7.0), Al3+ and total N properties could be detected by geostatistical analysis. A pure nugget effect was observed for the nutrients K, S and B, as well as macroporosity, mean weighted diameter of aggregates, and soil water storage. The cross validation procedure, based on linear regression and the determination coefficient, was more efficient to evaluate the quality of the adjusted mathematical model than the degree of spatial dependence. It was also concluded that the combination of classical with geostatistics can in many cases simplify the soil sampling process without losing information quality.

Influence of fungicide seed treatment on soybean nodulation and grain yield

Biological N2 fixation is a major factor contributing to the increased competitiveness of Brazilian soybeans on the international market. However, the contribution of this process may be limited by adverse conditions to symbiotic bacteria, such as fungicide seed treatments. This study aimed to evaluate the effects of the fungicides carbendazim + thiram and carboxin + thiram on soybean nodulation, plant growth and grain yield. Two field experiments were carried out in the Cerrado region of the State of Roraima, in a soil with a low organic matter content and no soybean bradyrhizobia. In 2005, seeds were treated with fungicide carbendazim + thiram and commercial inoculants containing the Bradyrhizobium elkanii strains SEMIA 5019 and SEMIA 587 and B. japonicum strains SEMIA 5079 and SEMIA 5080. In 2006, soybean seeds were treated with the fungicides carbendazim + thiram or carboxin + thiram and inoculated separately with each one of the four strains. The plants were evaluated for number of nodules and dry weight, shoot dry weight and total N accumulated in shoots 35 days after plant emergence, while grain yield and N grain content were determined at harvest. Both fungicides reduced soybean nodulation, especially in the presence of B. elkanii strains. The fungicide carbendazim + thiram reduced nodulation by about 50 % and grain yield by more than 20 % (about 700 kg ha-1), in the treatment inoculated with of strain SEMIA 587.

Sewage sludge as nitrogen and phosphorus source for cane-plant and first ratoon crops

The use of sewage sludge in Brazilian agriculture was regulated by the resolution no. 375 Conama, in 2006. However, there is a lack of research to adequate the mineral N and P fertilizer doses to be applied in agricultural fields treated with this residue. In a field experiment, the effects of application rates of sewage sludge and mineral N and P fertilizers on the productivity and technical characteristics of the cane-plant and first ratoon (residual effect) crops were evaluated. Four doses of sewage sludge (0, 3.6, 7.2 and 10.8 t ha-1, dry base), of N (0, 30, 60 and 90 kg ha-1) and of P2O5 (0, 60, 120 and 180 kg ha-1) were combined in a factorial and laid out on randomized block design, a with two replications. To evaluate the residual effect of the sludge, 120 kg ha-1 N and 140 kg ha-1 of K2O were applied in all plots. Sludge application at cane planting, with or without N and/or P fertilizer increased the stalk yield from 84 up to 118 t ha-1, with no alteration in the sugarcane quality, compared with the application of NPK fertilizer alone, resulting in a stalk yield of 91 t ha-1. The study of the response surface for stalk yield on lowfertility soil was the basis for a recommendation of mineral N and P fertilizer doses for sugarcane implantation as related to sewage sludge application rates. It was also concluded that a sludge application of 10.8 t ha-1, which is the sludge dose established based on the N criterion according to the resolution Conama nº 375, could a) reduce the use of mineral N by 100 % and of P2O5 by 30 %, with increments of 22 % in stalk yield, as a direct effect of sludge application to cane plant crop, and b) increase the stalk yield in the second harvest (first ratoon) by up to 12 % and sugar yield by up to 11 %, by the residual effect of sludge application to sugar cane.

Chemical and physical properties of organic residues

Due to human activity, large amounts of organic residue are generated daily. Therefore, an adequate use in agricultural activities requires the characterization of the main properties. The chemical and physical characterization is important when planning the use and management of organic residue. In this study, chemical and physical properties of charcoal, coffee husk, pine-bark, cattle manure, chicken manure, coconut fiber, sewage sludge, peat, and vermiculite were determined. The following properties were analyzed: N-NH4+, N-N0(3)-, and total concentrations of N, P, S, K, Ca, Mg, Mn, Zn, Cu, and B, as well as pH, Electrical Conductivity (EC) and bulk density. Coffee husk, sewage sludge, chicken manure and cattle manure were generally richer in nutrients. The EC values of these residues were also the highest (0.08 - 40.6 dS m-1). Peat and sewage sludge had the highest bulky density. Sodium contents varied from 0 to 4.75 g kg-1, with the highest levels in chicken manure, cattle manure and sewage sludge. Great care must be taken when establishing proportions of organic residues in the production of substrates with coffee husk, cattle or chicken manure or sewage sludge in the calculation of the applied fertilizer quantity in crop fertilization programs.

Relationship between soil oxidizable carbon and physical, chemical and mineralogical properties of umbric ferralsols

The occurrence of Umbric Ferralsols with thick umbric epipedons (> 100 cm thickness) in humid Tropical and Subtropical areas is a paradox since the processes of organic matter decomposition in these environments are very efficient. Nevertheless, this soil type has been reported in areas in the Southeast and South of Brazil, and at some places in the Northeast. Aspects of the genesis and paleoenvironmental significance of these Ferralsols still need a better understanding. The processes that made the umbric horizons so thick and dark and contributed to the preservation of organic carbon (OC) at considerable depths in these soils are of special interest. In this study, eight Ferralsols with a thick umbric horizon (UF) under different vegetation types were sampled (tropical rain forest, tropical seasonal forest and savanna woodland) and their macromorphological, physical, chemical and mineralogical properties studied to detect soil characteristics that could explain the preservation of high carbon amounts at considerable depths. The studied UF are clayey to very clayey, strongly acidic, dystrophic, and Al-saturated and charcoal fragments are often scattered in the soil matrix. Kaolinites are the main clay minerals in the A and B horizons, followed by abundant gibbsite and hydroxyl-interlayered vermiculite. The latter was only found in UFs derived from basalt rock in the South of the country. Total carbon (TC) ranged from 5 to 101 g kg-1 in the umbric epipedon. Dichromate-oxidizable organic carbon represented nearly 75 % of TC in the thick A horizons, while non-oxidizable C, which includes recalcitrant C (e.g., charcoal), contributed to the remaining 25 % of TC. Carbon contents were not related to most of the inorganic soil variables studied, except for oxalate-extractable Al, which individually explained 69 % (P < 0.001) of the variability of TC in the umbric epipedon. Clay content was not suited as predictor of TC or of the other studied C forms. Bulk density, exchangeable Al3+, Al saturation, ECEC and other parameters obtained by selective extraction were not suitable as predictors of TC and other C forms. Interactions between organic matter and poorly crystalline minerals, as indicated by oxalate-extractable Al, appear to be one of the possible organic matter protection mechanisms of these soils.

Long-term C-CO2 emissions and carbon crop residue mineralization in an oxisol under different tillage and crop rotation systems

Soil C-CO2 emissions are sensitive indicators of management system impacts on soil organic matter (SOM). The main soil C-CO2 sources at the soil-plant interface are the decomposition of crop residues, SOM turnover, and respiration of roots and soil biota. The objectives of this study were to evaluate the impacts of tillage and cropping systems on long-term soil C-CO2 emissions and their relationship with carbon (C) mineralization of crop residues. A long-term experiment was conducted in a Red Oxisol in Cruz Alta, RS, Brazil, with subtropical climate Cfa (Köppen classification), mean annual precipitation of 1,774 mm and mean annual temperature of 19.2 ºC. Treatments consisted of two tillage systems: (a) conventional tillage (CT) and (b) no tillage (NT) in combination with three cropping systems: (a) R0- monoculture system (soybean/wheat), (b) R1- winter crop rotation (soybean/wheat/soybean/black oat), and (c) R2- intensive crop rotation (soybean/ black oat/soybean/black oat + common vetch/maize/oilseed radish/wheat). The soil C-CO2 efflux was measured every 14 days for two years (48 measurements), by trapping the CO2 in an alkaline solution. The soil gravimetric moisture in the 0-0.05 m layer was determined concomitantly with the C-CO2 efflux measurements. The crop residue C mineralization was evaluated with the mesh-bag method, with sampling 14, 28, 56, 84, 112, and 140 days after the beginning of the evaluation period for C measurements. Four C conservation indexes were used to assess the relation between C-CO2 efflux and soil C stock and its compartments. The crop residue C mineralization fit an exponential model in time. For black oat, wheat and maize residues, C mineralization was higher in CT than NT, while for soybean it was similar. Soil moisture was higher in NT than CT, mainly in the second year of evaluation. There was no difference in tillage systems for annual average C-CO2 emissions, but in some individual evaluations, differences between tillage systems were noticed for C-CO2 evolution. Soil C-CO2 effluxes followed a bi-modal pattern, with peaks in October/November and February/March. The highest emission was recorded in the summer and the lowest in the winter. The C-CO2 effluxes were weakly correlated to air temperature and not correlated to soil moisture. Based on the soil C conservation indexes investigated, NT associated to intensive crop rotation was more C conserving than CT with monoculture.

Nutrient extraction and exportation by castor bean hybrid lyra

Information about nutrient extraction and exportation by crops, as well as the periods of highest nutrient demand is important for an adequate fertilization management. However, there are no studies on the nutrient uptake of short-stature hybrid castor bean. Therefore, the purpose of this study was to evaluate nutrient extraction and exportation by short-stature castor bean hybrid Lyra, in the spring-summer and fall-winter growing seasons. The experiments were conducted in the 2005/2006 spring-summer and 2006 fall-winter growing seasons on an Oxisol, in Botucatu, SP, in a randomized block design, with four replications. The plots consisted of plant samplings, which occurred 17, 31, 45, 59, 73, 97 and 120 days after emergence (DAE) in the spring-summer and 17, 31, 45, 59, 80, 100 and 120 DAE in fall-winter growing season. The growth of hybrid Lyra was slow and nutrient uptake lowest between emergence and the beginning of flowering. The period of highest dry matter (DM) accumulation rates and highest nutrient demand were observed 40 to 80 DAE, in both growing seasons. The order of nutrient extraction by the plants in the spring-summer growing season was: N>K>Ca>Mg>S>P>Fe>Mn>Zn>B>Cu>Mo. In fall-winter, S was more absorbed than Mg. Seed yield was higher in the spring-summer (2.995 kg ha-1), but nutrient extraction and exportation per ton of seed were similar in both growing seasons. Around 58 % of N and 84 % of P, and approximately half of the S and B absorbed throughout the cycle were exported with the seeds. However, most of the other nutrients accumulated in the plants returned to the soil in plant residues.

Multivariate analysis and geostatistics of the fertility of a humic rhodic hapludox under coffee cultivation

The spatial variability of soil and plant properties exerts great influence on the yeld of agricultural crops. This study analyzed the spatial variability of the fertility of a Humic Rhodic Hapludox with Arabic coffee, using principal component analysis, cluster analysis and geostatistics in combination. The experiment was carried out in an area under Coffea arabica L., variety Catucai 20/15 - 479. The soil was sampled at a depth 0.20 m, at 50 points of a sampling grid. The following chemical properties were determined: P, K+, Ca2+, Mg2+, Na+, S, Al3+, pH, H + Al, SB, t, T, V, m, OM, Na saturation index (SSI), remaining phosphorus (P-rem), and micronutrients (Zn, Fe, Mn, Cu and B). The data were analyzed with descriptive statistics, followed by principal component and cluster analyses. Geostatistics were used to check and quantify the degree of spatial dependence of properties, represented by principal components. The principal component analysis allowed a dimensional reduction of the problem, providing interpretable components, with little information loss. Despite the characteristic information loss of principal component analysis, the combination of this technique with geostatistical analysis was efficient for the quantification and determination of the structure of spatial dependence of soil fertility. In general, the availability of soil mineral nutrients was low and the levels of acidity and exchangeable Al were high.

Fertilization with filter cake and micronutrients in plant cane

The response of sugarcane to application of micronutrients is still not very well known. In view of the need for this information, the aim of this study was to evaluate the application of the micronutrients Zn, Cu, Mn, Fe, B, and Mo to plant cane in three soils, with and without application of filter cake. This study consisted of three experiments performed in the State of São Paulo, Brazil, (in Igaraçu do Tiete, on an Oxisol; in Santa Maria da Serra, on an Entisol, both in the 2008/2009 growing season; and in Mirassol, on an Ultisol, in the 2009/2010 growing season) in a randomized block design with four replications with a 8 x 2 factorial combination of micronutrients (1 - no application/control, 2 - addition of Zn, 3 - addition of Cu, 4 - addition of Mn 5 - addition of Fe, 6 - addition of B, 7 - addition of Mo, 8 - Addition of Zn, Cu, Mn, Fe, B, and Mo) and filter cake (0 and 30 t ha-1 of filter cake) in the furrow at planting. The application of filter cake was more efficient than of Borax in raising leaf B concentration to sufficiency levels for sugarcane in the Entisol, and it increased mean stalk yield in the Oxisol. In areas without filter cake application, leaf concentrations were not affected by the application of Zn, Cu, Mn, Fe, B, and Mo in the furrow at planting; however, Zn and B induced an increase in stalk and sugar yield in micronutrient-poor sandy soil.

Photosynthesis rate, chlorophyll content and initial development of physic nut without micronutrient fertilization

Few studies in Brazil have addressed the need for micronutrients of physic nut focusing on physiological responses, especially in terms of photosynthesis. The objective of this study was to evaluate the effects of omission of boron (B), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) on Jatropha curcas L.. The experimental design was a randomized block with four replications. The treatments were complete solution (control) and solution without B, Cu, Fe, Mn, and Zn. We evaluated the chlorophyll content (SPAD units), photosynthetic rate, dry matter production and accumulation of micronutrients in plants, resulting from different treatments. The first signs of deficiency were observed for Fe and B, followed by Mn and Zn, while no symptoms were observed for Cu deficiency. The micronutrient omission reduced the dry matter yield, chlorophyll content and photosynthetic rate of the plants differently for each omitted nutrient. It was, however, the omission of Fe that most affected the development of this species in all parameters evaluated. The treatments negatively affected the chlorophyll content, evaluated in SPAD units, and the photosynthetic rate, except for the omission of B. However this result was probably due to the concentration effect, since there was a significant reduction in the dry matter production of B-deficient plants.

Upland rice under no-tillage preceded by crops for soil cover and nitrogen fertilization

The grain yield of upland rice under no-tillage has been unsatisfactory and one reason could be the nitrate/ammonium balance in the soil. Cover crops and nitrogen fertilization can be used to change the nitrate/ammonium relation in the soil and improve conditions for the development of upland rice in the no-tillage (NT) system. The aim was to study the effect of cover crops and nitrogen sources on grain yield of upland rice under no tillage. The study was carried out on the Fazenda Experimental Lageado, in Botucatu, State of São Paulo, Brazil, in an Oxisol area under no-tillage for six years. The experiment was arranged in a randomized block split-plot design with four replications. The plots consisted of six cover crop species (Brachiaria brizantha, B. decumbens, B. humidicola, B. ruziziensis, Pennisetum americanum, and Crotalaria spectabilis) and the split-plots of seven forms of N fertilizer management. Millet is the best cover crop to precede upland rice under NT. The best form of N application, as nitrate, is in split rates or total rate at topdressing or an ammonium source with or without a nitrification inhibitor, in split doses. When the cover crops C. spectabilis, B. brizantha, B. decumbens, B. humidicola, and B. ruziziensis preceded rice, they induced the highest grain yield when rice was fertilized with N as ammonium sulfate source + nitrification inhibitor in split rates or total dose at topdressing.

Three-dimensional interpolation of soil data: fertility and pedomorphological features in southern Brazil

The graphical representation of spatial soil properties in a digital environment is complex because it requires a conversion of data collected in a discrete form onto a continuous surface. The objective of this study was to apply three-dimension techniques of interpolation and visualization on soil texture and fertility properties and establish relationships with pedogenetic factors and processes in a slope area. The GRASS Geographic Information System was used to generate three-dimensional models and ParaView software to visualize soil volumes. Samples of the A, AB, BA, and B horizons were collected in a regular 122-point grid in an area of 13 ha, in Pinhais, PR, in southern Brazil. Geoprocessing and graphic computing techniques were effective in identifying and delimiting soil volumes of distinct ranges of fertility properties confined within the soil matrix. Both three-dimensional interpolation and the visualization tool facilitated interpretation in a continuous space (volumes) of the cause-effect relationships between soil texture and fertility properties and pedological factors and processes, such as higher clay contents following the drainage lines of the area. The flattest part with more weathered soils (Oxisols) had the highest pH values and lower Al3+ concentrations. These techniques of data interpolation and visualization have great potential for use in diverse areas of soil science, such as identification of soil volumes occurring side-by-side but that exhibit different physical, chemical, and mineralogical conditions for plant root growth, and monitoring of plumes of organic and inorganic pollutants in soils and sediments, among other applications. The methodological details for interpolation and a three-dimensional view of soil data are presented here.

Physiological and morphological responces of Brachiaria spp. to flooding

The physiological and morphological responses of the forage grasses Brachiaria brizantha cv. Marandu, B. decumbens and B. humidicola were compared for plants grown in pots under flooding and well-drained conditions for 14 days. Flooding reduced specific leaf area and biomass allocation to roots in all species and enhanced leaf senescence in B. brizantha and B. decumbens. Relative growth rate was reduced by flooding in B. brizantha and B. decumbens, but not in B. humidicola.Leaf elongation rate was unaffected by flooding in B. decumbens and B. humidicola, but declined in B. brizantha since the first day of flooding. Net photosynthesis and leaf chlorophyll content were reduced by flooding in B. brizantha; however, no flooding effect could be detected in the other two species. For all species, there was a close relationship between net photosynthesis and stomatal conductance under flooding. These results show that the studied species have distinct degrees of tolerance to flood, B. brizantha is intolerant, B. decumbens is moderately tolerant and B. humidicola is tolerant. Because leaf elongation rate was immediately depressed by flooding only in B. brizantha, this measurement could be appropriate as an early detection mechanism for relative flood tolerance in Brachiaria spp.