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.

Maize response to nitrogen fertilization timing in two tillage systems in a soil with high organic matter content

No-tillage systems, associated to black oat as preceding cover crop, have been increasingly adopted. This has motivated anticipated maize nitrogen fertilization, transferring it from the side-dress system at the stage when plants have five to six expanded leaves to when the preceding cover crop is eliminated or to maize sowing. This study was conducted to evaluate the effects of soil tillage system and timing of N fertilization on maize grain yield and agronomic efficiency of N applied to a soil with high organic matter content. A three-year field experiment was conducted in Lages, state of Santa Catarina, from 1999 onwards. Treatments were set up in a split plot arrangement. Two soil tillage systems were tested in the main plots: conventional tillage (CT) and no-tillage (NT). Six N management systems were assessed in the split-plots: S1 - control, without N application; S2 - all N (100 kg ha-1) applied at oat desiccation; S3 - all N applied at maize sowing; S4 - all N side-dressed when maize had five expanded leaves (V5 growth stage); S5 - 1/3 of N rate applied at maize sowing and 2/3 at V5; S6 - 2/3 of nitrogen rate applied at maize sowing and 1/3 at V5. Maize response to the time and form of splitting N was not affected by the soil tillage system. Grain yield ranged from 6.0 to 11.8 t ha-1. The anticipation of N application (S2 and S3) decreased grain yield in two of three years. In the rainiest early spring season (2000/2001) of the experiment, S4 promoted an yield advantage of 2.2 t ha-1 over S2 and S3. Application of total N rate before or at sowing decreased the number of kernels produced per ear in 2000/2001 and 2001/2002 and the number of ears produced per area in 2001/2002, resulting in reduced grain yield. The agronomic efficiency of applied N (kg grain increase/kg of N applied) ranged from 13.9 to 38.8 and was always higher in the S4 than in the S2 and S3 N systems. Short-term N immobilization did not reduce grain yield when no N was applied before or at maize sowing in a soil with high organic matter content, regardless of the soil tillage system.

Potential use of a chemical leaching reject from a kaolin industry as agricultural fertilizer

The industrial refining of kaolin involves the removal of iron oxides and hydroxides along with other impurities that cause discoloration of the final product and depreciate its commercial value, particularly undesirable if destined to the paper industry. The chemical leaching in the industrial processing requires treatments with sodium hyposulfite, metallic zinc, or sulfuric and phosphoric acids, in order to reduce, dissolve and remove ferruginous compounds. To mitigate the environmental impact, the acidic effluent from the leaching process must be neutralized, usually with calcium oxide. The resulting solid residue contains phosphorous, zinc, and calcium, among other essential nutrients for plant growth, suggesting its use as a macro and micronutrient source. Samples of such a solid industrial residue were used here to evaluate their potential as soil fertilizer in an incubation greenhouse experiment with two soil samples (clayey and medium-textured). The small pH shift generated by applying the residue to the soil was not a limiting factor for its use in agriculture. The evolution of the concentrations of exchangeable calcium, and phosphorous and zinc extractability by Mehlich-1 extractant during the incubation period confirms the potential use of this industrial residue as agricultural fertilizer.

The effect of nitrogen and sulphur fertilization on yield and quality of kohlrabi (Brassica oleracea, L.)

In a greenhouse pot experiment with kohlrabi, variety Luna, we explored the joint effect of N (0.6 g N per pot = 6 kg of soil) and S in the soil (25-35-45 mg kg-1 of S) on yields, on N, S and NO3- content in tubers and leaves, and on alterations in the amino acids concentration in the tubers. S fertilisation had no effect on tuber yields. The ranges of N content in tubers and leaves were narrow (between 1.42-1.48 % N and 1.21-1.35 % N, respectively) and the effect of S fertilisation was insignificant. S concentration in the tubers ranged between 0.59 and 0.64 % S. S fertilisation had a more pronounced effect on the S concentration in leaf tissues where it increased from 0.50 to 0.58 or to 0.76 % S under the applied dose. The NO3- content was higher in tubers than in leaves. Increasing the S level in the soil significantly reduced NO3- concentrations in the tubers by 42.2-53.6 % and in the leaves by 8.8-21.7 %. Increasing the S content in the soil reduced the concentration of cysteine + methionine by 16-28 %. The values of valine, tyrosine, aspartic acid and serine were constant. In the S0, S1, and S2 treatments the levels of threonine, isoleucine, leucine, arginine, the sum of essential amino acids and alanine decreased from 37 to 9 %. The histidine concentration increased with increasing S fertilisation. S fertilisation of kohlrabi can be recommended to stabilize the yield and reduce the undesirable NO3- contained in the parts used for consumption.

Soil carbon and nitrogen in pasture soil reforested with eucalyptus and guachapele

In spite of the normally low content of organic matter found in sandy soils, it is responsible for almost the totality of cation exchange capacity (CEC), water storage and availability of plant nutrients. It is therefore important to evaluate the impact of alternative forest exploitation on the improvement of soil C and N accumulation on these soils. This study compared pure and mixed plantations of Eucalyptus grandis and Pseudosamanea guachapele, a N2-fixing leguminous tree, in relation to their effects on soil C and N stocks. The studied Planosol area had formerly been covered by Panicum maximum pasture for at least ten years without any fertilizer addition. To estimate C and N contents, the soil was sampled (at depths of 0-2.5; 2.5-5.0; 5.0-7.5; 7.5-10.0; 10.0-20.0 and 20.0-40.0 cm), in pure and mixed five-year-old tree plantations, as well as on adjacent pasture. The natural abundance 13C technique was used to estimate the contribution of the soil organic C originated from the trees in the 0-10 cm soil layer. Soil C and N stocks under mixed plantation were 23.83 and 1.74 Mg ha-1, respectively. Under guachapele, eucalyptus and pasture areas C stocks were 14.20, 17.19 and 24.24 Mg ha-1, respectively. For these same treatments, total N contents were 0.83; 0.99 and 1.71 Mg ha-1, respectively. Up to 40 % of the soil organic C in the mixed plantation was estimated to be derived from trees, while in pure eucalyptus and guachapele plantations these same estimates were only 19 and 27 %, respectively. Our results revealed the benefits of intercropped leguminous trees in eucalyptus plantations on soil C and N stocks.

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.

Relationships between grain yield and accumulation of biomass, nitrogen and phosphorus in common bean cultivars

Shoot biomass is considered a relevant component for crop yield, but relationships between biological productivity and grain yield in legume crops are usually difficult to establish. Two field experiments were carried out to investigate the relationships between grain yield, biomass production and N and P accumulation at reproductive stages of common bean (Phaseolus vulgaris) cultivars. Nine and 18 cultivars were grown on 16 m² plots in 1998 and 1999, respectively, with four replications. Crop biomass was sampled at four growth stages (flowering R6, pod setting R7, beginning of pod filling R8, and mid-pod filling R8.5), grain yield was measured at maturity, and N and P concentrations were determined in plant tissues. In both years, bean cultivars differed in grain yield, in root mass at R6 and R7 stages, and in shoot mass at R6 and R8.5, whereas at R7 and R8 differences in shoot mass were significant in 1998 only. In both years, grain yield did not correlate with shoot mass at R6 and R7 and with root mass at R6. Grain yield correlated with shoot mass at R8 in 1999 but not in 1998, with shoot mass at R8.5 and with root mass at R7 in both years. Path coefficient analysis indicated that shoot mass at R8.5 had a direct effect on grain yield in both years, that root mass at R7 had a direct effect on grain yield in 1998, and that in 1999 the amounts of N and P in shoots at R8.5 had indirect effects on grain yield via shoot mass at R8.5. A combined analysis of both experiments revealed that biomass accumulation, N and P in shoots at R6 and R7 as well as root mass at R6 were similar in both years. In 1998 however bean accumulated more root mass at R7 and more biomass and N and P in shoots at R8 and R8.5, resulting in a 57 % higher grain yield in 1998. This indicates that grain yield of different common bean cultivars is not intrinsically associated with vegetative vigor at flowering and that mechanisms during pod filling can strongly influence the final crop yield. The establishment of a profuse root system during pod setting, associated with the continuous N and P acquisition during early pod filling, seems to be relevant for higher grain yields of common bean.

Green manure in coffee systems in the region of Zona da Mata, Minas Gerais: characteristics and kinetics of carbon and nitrogen mineralization

The use of green manure may contribute to reduce soil erosion and increase the soil organic matter content and N availability in coffee plantations in the Zona da Mata, State of Minas Gerais, in Southeastern Brazil. The potential of four legumes (A. pintoi, C. mucunoides, S. aterrimum and S. guianensis) to produce above-ground biomass, accumulate nutrients and mineralize N was studied in two coffee plantations of subsistence farmers under different climate conditions. The biomass production of C. mucunoides was influenced by the shade of the coffee plantation. C. mucunoides tended to mineralize more N than the other legumes due to the low polyphenol content and polyphenol/N ratio. In the first year, the crop establishment of A. pintoi in the area took longer than of the other legumes, resulting in lower biomass production and N2 fixation. In the long term, cellulose was the main factor controlling N mineralization. The biochemical characteristics, nutrient accumulation and biomass production of the legumes were greatly influenced by the altitude and position of the area relative to the sun.

Root system distribution of sugar cane as related to nitrogen fertilization, evaluated by two methods: monolith and probes

Few studies on sugar cane have evaluated the root system of the crop, in spite of its importance. This is mainly due to the difficulty of evaluation and high variability of results. The objective of this study was to develop an evaluation method of the cane root system by means of probes so as to evaluate the mass, distribution and metabolically active roots related to N fertilization at planting. For this purpose, an experiment was conducted in an Arenic Kandiustults with medium texture in Jaboticabal/SP, in a randomized block design with four replications and four treatments: control (without N) and 40, 80 and 120 kg ha-1 of N applied in the form of urea in the planting furrow of the cane variety SP81 3250. One week before harvest, a urea-15N solution was applied at the cane stalk base to detect active metabolism in the root system. Trenches of 1.5 m length and 0.6 m depth were opened between two sugar cane rows for root sampling by two methods: monoliths (0.3, 0.2 and 0.15 m wide, deep and long respectively) taken from the trench wall and by probe (internal diameter 0.055 m). For each method, 15 samples per plot were collected. The roots were separated from the soil in a sieve (2 mm mesh), oven-dried (at 65 ºC) and the dry matter was measured. Root sampling by probes resulted in root mass that did not differ from the evaluation in monoliths, indicating that this evaluation method may be used for sugar cane root mass, although neither the root distribution in the soil profile nor the rhizome mass were efficiently evaluated, due to the small sample volume. Nitrogen fertilization at planting did not result in a greater root accumulation in the sugar cane plant, but caused changes in the distribution of the root system in the soil. The absence of N fertilization led to a better root distribution in the soil profile, with 50, 34 and 16 % in the 0-0.2, 0.2-0.4 and 0.4-0.6 m layers, respectively; in the fertilized treatments the roots were concentrated in the surface layer, with on average 70, 17 and 13 % for the same layers. The metabolically active roots were concentrated in the center of the cane stool, amounting to 40 % of the total root mass, regardless of N fertilization (application of 120 kg ha-1 N or without N).

Response of irrigated wheat cultivars to different nitrogen rates and sources

High wheat yields require good N fertilization management. The objective of this study was to evaluate the effects of different N applications at sowing using Entec (N source with nitrification inhibitor) and urea (traditional N source) at covering, on four wheat cultivars. The experiment was conducted in a randomized block design in a factorial scheme, with four replications, at the Experimental Station of the Faculdade de Engenharia de Ilha Solteira - UNESP, on a dystrophic, epi-eutrophic alic Red Latosol with loamy texture, formerly under savannah vegetation. Four N rates (0, 60, 120, and 180 kg ha-1) were tested, applied at sowing in the case of Entec and top-dressed 40 days after plant emergence in the case of urea, and the four wheat cultivars E 21, E 22, E 42, and IAC 370. The yield of the wheat cultivars E 21 and E 42 was highest. Plant height and lodging index of cultivar E 22 were greatest, with consequently lowest grain yield. There was no significant difference between Entec (applied at sowing) and urea (top-dressed) in terms of grain yield and yield components. Nevertheless, urea resulted in a higher N leaf content, and Entec in a larger number of undeveloped spikelets. High nitrogen rates influenced the hectoliter mass negatively, affecting wheat grain quality. Grain yield increased under N rates of up to 82 kg ha-1 N, through Entec applied at sowing or top-dressed urea.

Spatial variability of soil chemical properties after coffee tree removal

Assessing the spatial variability of soil chemical properties has become an important aspect of soil management strategies with a view to higher crop yields with minimal environmental degradation. This study was carried out at the Centro Experimental of the Instituto Agronomico, in Campinas, São Paulo, Brazil. The aim was to characterize the spatial variability of chemical properties of a Rhodic Hapludox on a recently bulldozer-cleaned area after over 30 years of coffee cultivation. Soil samples were collected in a 20 x 20 m grid with 36 sampling points across a 1 ha area in the layers 0.0-0.2 and 0.2-0.4 m to measure the following chemical properties: pH, organic matter, K+, P, Ca2+, Mg2+, potential acidity, NH4-N, and NO3-N. Descriptive statistics were applied to assess the central tendency and dispersion moments. Geostatistical methods were applied to evaluate and to model the spatial variability of variables by calculating semivariograms and kriging interpolation. Spatial dependence patterns defined by spherical model adjusted semivariograms were made for all cited soil properties. Moderate to strong degrees of spatial dependence were found between 31 and 60 m. It was still possible to map soil spatial variability properties in the layers 0-20 cm and 20-40 cm after plant removal with bulldozers.

Bermuda grass sod production as related to nitrogen rates

Of all nutrients, N has the strongest effect on grass growth and an adequate N fertilization can reduce the time required for the formation of high-quality mats. This study aimed to evaluate the influence of N fertilization on Bermuda grass sod production and quality. The experiment was conducted in an area of commercial sod production, in Capela do Alto, state of São Paulo. Cynodon dactylon (Pers) L., known as Bermuda grass, was evaluated in a randomized complete block design with five treatments and four replications. Treatments consisted of five N rates: 0, 150, 300, 450 and 600 kg ha-1. Increasing N applications to Bermuda grass increased the soil cover rate, reducing the time required for mat formation. The accumulation of rhizome + root + stolon dry matter was highest at a rate of 354 kg ha-1 N and the mat resistance to breakage at a rate of 365 kg ha-1 N. Nitrogen rates between 354 and 365 kg ha-1 increased mat resistance and consequently the suitability for postharvest handling, tending to improve the efficiency in the area.

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.

Nitrate reductase activity and spad readings in leaf tissues of guinea grass submitted to nitrogen and potassium rates

Nitrogen and K deficiency are among the most yield limiting factors in Brazilian pastures. The lack of these nutrients can hamper the chlorophyll biosynthesis and N content in plant tissues. A greenhouse experiment was carried out to evaluate the relationship among N and K concentrations, the indirect determination of chlorophyll content (SPAD readings), nitrate reductase activity (RNO3-) in newly expanded leaf lamina (NL) and the dry matter yield for plant tops of Mombaça grass (Panicum maximum Jacq.). A fractionated 5² factorial design was used, with 13 combinations of N and K rates in the nutrient solution. The experimental units were arranged in a randomized block design, with four replications. Plants were harvested twice. The first harvest occurred 36 days after seedling transplanting and the second 29 days after the first. Significance occurred for the interaction between the N and K rates to SPAD readings and to RNO3- assessment taken on the NL during the first growth. Besides, RNO3- and SPAD readings increased only with the NL N concentration, reaching the highest values of both variables up to about 25 g kg-1, but were ratively constant at higher leaf N. Significant relationships either between SPAD readings or RNO3- activity and shoot dry mass weight were also observed. The critical levels of N concentration in the NL were, respectively, 22 and 17g kg-1 in the first and second harvest. Thus, SPAD instrument and RNO3- assessment can be used as complementary tools to evaluate the N status in forage grass.

Seeds enriched with phosphorus and molybdenum improve the contribution of biological nitrogen fixation to common bean as estimated by 15n isotope dilution

Seeds with a high concentration of P or Mo can improve the growth and N accumulation of the common bean (Phaseolus vulgaris L.), but the effect of enriched seeds on biological N2 fixation has not been established yet. This study aimed to evaluate the effect of seeds enriched with P and Mo on growth and biological N2 fixation of the common bean by the 15N isotope dilution technique. An experiment was carried out in pots in a 2 x 3 x 2 x 2 factorial design in randomized blocks with four replications, comprising two levels of soil applied P (0 and 80 mg kg-1), three N sources (without N, inoculated with rhizobia, and mineral N), two seed P concentrations (low and high), and two seed Mo concentrations (low and high). Non-nodulating bean and sorghum were used as non-fixing crops. The substrate was 5.0 kg of a Red Latosol (Oxisol) previously enriched with 15N and mixed with 5.0 kg of sand. Plants were harvested 41 days after emergence. Seeds with high P concentration increased the growth and N in shoots, particularly in inoculated plants at lower applied P levels. Inoculated plants raised from high P seeds showed improved nodulation at both soil P levels. Higher soil P levels increased the percentage of N derived from the atmosphere (%Ndfa) in bean leaves. Inoculation with the selected strains increased the %Ndfa. High seed P increased the %Ndfa in inoculated plants at lower soil P levels. High seed Mo increased the %Ndfa at lower soil P levels in plants that did not receive inoculation or mineral N. It is concluded that high seed P concentration increases the growth, N accumulation and the contribution of the biological N2 fixation in the common bean, particularly in inoculated plants grown at lower soil P availability.