C. A. Vasconcellos

Urease activity and its relation to soil organic matter, microbial biomass nitrogen and urea-nitrogen assimilation by maize in a Brazilian Oxisol under no-tillage and tillage systems.

Abstract We studied the relationship between urease activity (UA) and soil organic matter (SOM), microbial biomass N (Nbiom) content, and urea-N fertilizer assimilation by maize in a Dark Red Latosol (Typic Haplustox) cultivated for 9 years under no-tillage (NT), tillage with a disc plough (DP), and tillage with a moldboard plough (MP). Two soil depths were sampled (0–7.5 cm and 7.5–15 cm) at 4 different times during the crop cycle. Urea was applied at four different rates, ranging from 0 to 240 kg N ha–1. The levels of fertilizer N did not affect the UA, SOM content, and Nbiom content. No significant difference between the treatments (NT, DP, and MP) was observed for SOM during the experiment, probably because the major part of the SOM was in recalcitrant pools, since the area was previously cultivated (conventional tillage) for 20 years. The Nbiom content explained 97% and 69% of the variation in UA in the upper and deeper soil layer, respectively. UA and biomass N were significantly higher in the NT system compared to the DP and MP systems. The highest maize productivity and urea-N recovery was also observed for the NT system. We observed that the increase in urea-N losses under NT, possibly as a consequence of a higher UA, was compensated for by the increase in N immobilized in the biomass.

Relação entre o zinco "disponível", por diferentes extratores, e as frações de zinco em amostras de solos

Many extracting procedures for the plant-available zinc have been developed. Total soil Zn fractionation has been used as an attempt to understand the reactions of this nutrient in soils and the behaviour of the extracting procedures. This work evaluated the influence of soil characteristics on the concentration of Zn extracted by different procedures and on soil Zn fractions. Samples were collected from the 0-20 cm surface layer of twelve soils, representing the great soil groups of Dark-Red Latosol (LE), Red-Yellow Latosol (LV), Yellow Latosol (LA), Red-Yellow Podzolic (PV), and Quartzi Psaments (AQ). The soil samples received 0 and 20 mg dm-3 of Zn and were incubated for 30 days. Soil Zn concentration was determined after extraction with DTPA-TEA-CaCL2, 0.1 mol L-1 HCl, Mehlich-1 (M-1) and Mehlich-3 (M-3). Zinc fractionation was also carried out to determine exchangeable Zn (ExZn), Zn tied up to organic matter (OmZn), to manganese oxide (MnZn), to amorphous iron oxide (AFeZn), and to crystalline iron oxide (CFeZn). DTPA and M-3 were the extractants with larger sensitivity to the soil characteristics related to the capacity factor (buffering power). The M-1 and HCl extractants presented lower sensitivity and lower correlation with these characteristics due to their larger extraction power. The ratio Zn recovered by the extractant/Zn applied to the soil showed the best correlation with soil characteristics related to the Zn capacity factor. Exchangeable Zn fraction was the largest source of this nutrient to the tested extractants. The fractions of ExZn, OmZn, MnZn AFeZn and CFeZn did not account for the zinc recovered by the extractants, in all cases.

Aluminum effects on growth, grain yield and nutrient use efficiency ratios in sorghum genotypes

Sorghum (Sorhum bicolor L. Moench) is an important cereal crop of the world. Performance of sorghum in acid infertile soils that are common to the tropics is rather poor. Research was undertaken in greenhouse and field conditions to evaluate the differences in growth, grain yield, and nutrient efficiency ratio (NER) of sorghum genotypes grown at three levels of Al saturation. The growth of shoots and roots and the grain yields showed significant differences with respect to Al-saturation, genotypes and their interactions. The shoot weights, root weights, and visual scores of the greenhouse study were highly related to grain yields obtained in field. The greenhouse technique adapted in this study appears to be a reliable method for separation of genotypes into Al-tolerant and intolerant types. The NER values helped differentiate genotypes into efficient and inefficient utilizers of the absorbed nutrients. The sorghum entries showed intraspecific genetic diversity in growth and NER values for the essential elements in the presence or absence of toxic levels of Al. We concluded that selection of acid soil tolerant genotypes and further breeding of acid soil (Al) tolerant cultivars is feasible in sorghum.

Evolvimento de dióxido de carbono e mineralização de nitrogênio em Latossolo Vermelho-Escuro com diferentes manejos

The objective of this work was to verify the influence of different types of straw (maize and lablab) and soil management on evolving CO2 and N mineralization. A dystrophic clayey Dark-Red Latosol under Cerrado from the region of Sete Lagoas, MG, Brazil, was cultivated during five years with no-tillage, disc-plow and moldboard-plow. Soil samples (0-20 cm) were incubated at 25oC during 55 days, with and without N fertilizer applied at the beginning and 25 days afterwards. As a general rule, the maize straw had higher rates of evolved CO2 than the lablab (935 e 764 mg CO2 g-1 soil, respectively). The type of straw influenced the amount of CO2 evolved more than the type of soil management did. Nitrogen addition increases the rate of CO2 evolved only when applied at the beginning of the incubation period. The N availability and the duration of the immobilization are modified by the C/N ratio and by the type of soil management.

Acúmulo de nitrogênio e de fósforo em plantas de milho afetadas pelo suprimento parcial de fósforo às raízes

Two split root trials were carried out in nutrient solution to evaluate nitrogen accumulation as a function of phosphorus supply applied in partial contact to maize roots. After a seven day growth period in complete nutrient solution, maize seedlings were transplanted to joint pots containing 1.6 L of nutrient solution. Roots were equally shared between the pots. In the first trial, two phosphorus levels (0.02 mmol L-1 and 0.1 mmol L-1) and phosphorus and nitrogen placement were evaluated. In the second trial, two nitrogen sources (nitrate and ammonium) and the same nitrogen and phosphorus placement design adopted in the first trial were assessed. There was a greater phosphorus accumulation in the shoots as a consequence of phosphorus supplied to the whole root system as compared to just half of it. Phosphorus supplied to part of the root system did not properly provide this nutrient to the other part, a fact which raises the possibility of inner phosphorus cycling problems in maize plants. These results were verified for nitrogen as well. When jointly supplied to the whole root system, nitrogen and phosphorus caused greater accumulation of nitrogen in the shoots.

Mechanisms of phosphorus efficiency in maize

The National Maize and Sorghum Research Center of the Brazilian Agricultural Research Corporation, has been working for the past two decades to increase plant adaptation to low P levels in acid soils. We have studied several mechanisms in order to clarify the differences between genotypes in relation to phosphorus efficiency using maize standards for phosphorus efficiency developed at Embrapa Maize and Sorghum.

Resíduos de sorgo e a mineralização do nitrogênio em LATOSSOLO VERMELHO fase cerrado

Management alterations induce significant modifications on organic matter quality and quantity, on N quantity and forms and on the mineralization process. The aim of this work was to study the influence of straw on the N mineralization rates of the N-NH4+ and N-NO3 forms during the decomposition of residues of two sorghum genotypes. The experimental design consisted of a 3x2x3 complete block outline, including two soil managements, three cultural residues and two nitrogen levels, with three replications. Percolation tubes were prepared with 20 g of soil mixed with 20 g of sand. Each tube with soil and sand received 0.1g residual straw from the two sorghum genotypes, with and without 50 mg N kg-1 in the form of ammonium nitrate. A control treatment was maintained without straw in the presence and absence of N. After an initial seven day incubation period, N was extracted weekly, over 49 days, using 100 mL of 0.01 mol L-1 CaCl2. The forms N-NH4+ and N-NO3- were determined spectroscoptically (UV/VIS) in the percolated extracts. N mineralization dependent on sorghum genotype and applied N. Sorghum straw influenced time and amount of N mineralized. The N-NH4+/ N-NO3- ratio showed variability during the incubation time as influenced by the incorporated residue. That ratio increased up to fifteen days of incubation time and decreased in subsequent periods. Without residues the mineralization potential was higher in the N-NO3 form.

Preparo do solo e adubação nitrogenada na produtividade do milho em latossolo sob vegetação de cerrado

The effects of soil preparation systems and doses of nitrogen on total dry matter, straw and grain production and on nitrogen accumulation by corn plants (Zea mays L.) cultivated under irrigation were evaluated in a field experiment in a Dark-Red Latosol (Oxisol), originally under cerrado vegetation, at EMBRAPA/CNPMS experimental station, Sete Lagoas, Minas Gerais State, Brazil, from November, 1995 to June, 1996. The soil preparation systems studied were: no till, conventional till with disk plow and conventional till with moldboard plow. The nitrogen doses were: 0, 60, 120 and 240 kg ha-1 N, applied in cover. The highest productions of dry matter yield and grains and accumulated nitrogen were obtained in the no till system. The plants did not linearly respond to N application, considering the straw and grain production. The greatest efficiency of N utilization by the crop occurred in the no till system, in the 60 kg ha-1 N, as evidenced by the highest recover of applied N.

Preparo do solo e adubação nitrogenada na produção de grãos e matéria seca e acúmulo de nutrientes pelo milho

The effects of soil preparation and doses of nitrogen on grain and straw dry matter production and N, P, K, Ca, Mg, S and Zn accumulation by corn plants (Zea mays L.) cultivated under irrigation were evaluated in a field experiment in a Dark Red Latosol (Oxisol), originally under cerrado vegetation, at Embrapa-Centro Nacional de Pesquisa de Milho e Sorgo experimental station, in Sete Lagoas, MG, Brazil, from November, 1995 to June, 1996. The soil preparation systems studied were: no till, conventional till with disk plow and conventional till with moldboard plow. The nitrogen doses were: 0, 60, 120 and 240 kg ha-1 N, applied in cover. The highest productions of grains and straw dry matter and nutrients accumulation were obtained in the no till system. In the doses of 60 kg ha-1 N, the greatest efficiency and the highest recover of applied N by the crop occurred.

Fluxo difusivo de zinco em amostras de solo influenciado por textura, íon acompanhante e pH do solo

The diffusive flux (diffusion) is the main form of zinc transport in soil, due to its low concentration in solution. This work aimed to evaluate the diffusion of Zn in samples of three soil types: a loamy texture Dark-Red Latosol (LE), a medium texture Red-Yellow Podzolic (PV), and a sandy texture Red-Yellow Latosol (LV). The diffusion was assessed in samples with the natural pH for the three soil samples and at pH 5.40 for the LE and 6.00 for the PV. Three sources of Zn (ZnCl2, ZnEDTA and ZnSO4) at the rates of 0, 20 and 40 mg dm-3 of Zn were tested. The experimental units were constituted of 400 cm3 of soil placed in PVC rings, 10 cm of diameter and 5 cm high. At the depth of 2.5 cm, a slide of a strong acid exchange cation resin (CR61CZR IONICS, INC.)as a sink for Zn, with the dimensions of 2.0 x 5.0 cm was set. The soil samples were moistened to the field capacity and incubated for 15 days. Then, the resin slides were removed and submitted to the extraction of Zn. Soil pH was an important factor controlling Zn diffusion, which decreased with pH increase. In general, Zn diffusive flux was lower with the increase of the soil clay content. The diffusive flux of Zn was greater in the three soils, when the source was ZnCl2.