Helena Rimski-Korsakov

Late season nitrogen fertilization of soybeans: effects on leaf senescence, yield and environment

Nitrogen demand from soybean seeds during seed filling is very high and has been proposed as the cause of nitrogen remobilization and leaf senescence. Previous research has not shown consistent effects of late season fertilization on seed yield, while its effects on leaf senescence have not been evaluated. Two field experiments were performed to determine the effects of a late season N fertilization on leaf senescence and fall, seed yield and its components, and residual soil nitrate, and to evaluate the potential risk of groundwater contamination. Two rates of nitrogen (50 and 100 kg N ha−1) were applied at the R3 and R5 development stages. Nitrogen fertilization, either at R3 or R5, increased soil nitrate availability during the seed-filling period. Seed yield, seed number and protein content were not affected by N fertilization. The addition of 100 kg N ha−1 produced a small delay of 1–2 days in the leaf fall, and slightly increased seed size (3.6%). Our results suggest that increasing soil N availability during the seed-filling period is not an effective way to delay leaf senescence or to increase seed growth and yield of soybean. Nitrogen fertilization increased the level of residual nitrate in the top soil at one site (the one with lowest seed yield), increasing the risk of nitrate leaching during subsequent fallow.

Effect of Water Stress in Maize Crop Production and Nitrogen Fertilizer Fate

ABSTRACT Maize production is affected by water and nitrogen (N) deficit either separately or joined, but this fact is not completely defined. The aim was to evaluate the fate of N in maize fertilized and subjected to water stress in controlled conditions. A greenhouse experiment was carried out at the University of Buenos Aires campus. The design was a 2 × 2 factorial with four replications. The factors were N: 70 and 140 kg N ha−1 as labeled urea (15N), and water: 100% or 50% of the potential evapotranspiration. The harvest of aerial and root biomass was carried out at R1 stage. Nitrogen in plants, soils nitrate, ammonia volatilization, and 15N percentage were determined. Obtained results only partially agree with previous research. Water stress depressed aerial biomass production independently of N doses. When water was limiting, the uptake of N from fertilizer was independent of N. When water was not limiting, N uptake increased with the higher N doses. Volatilization losses were 3.7 to 7.8% of N applied as fertilizer. Plant N recovers was around 45% of the N applied, except in treatment water stressed with high N rate (19%). Nitrate-N from the fertilizer in the soil at harvest and accumulated N from the fertilizer in plant were lineally related (r2 = 0.54; p < 0.001). Important destinations of N were accumulation in plant, volatilization and incorporation into soil organic matter. However, residual nitrate was a main fate in heavily fertilized and water deficit treatment. This process could lead to the eventual nitrate leaching.

Cover crops in the agricultural systems of the Argentine Pampas

The Argentine Pampas (figure 1) is located in the south cone of South America (31° to 39° S and 58° to 65° W). The region extends along 55 to 60 million ha (135 to 148 million ac) and was originally covered with temperate grasslands. The region shows several similarities as well as differences with their equivalent grassland of North America. In a simplified picture, the climate is humid in the east and subhumid/semiarid in the west. Rainfall varies from 1,200 mm y−1 (47 in yr−1) in the east to 500 mm y−1 (20 in yr−1) in the west. Fall and spring/summer are the rainier seasons but there is considerable variability in monthly and annual precipitation. The Pampas is classified as mesothermal, with average temperature around 14°C (57.2°F) in the south and 20°C (68°F) in the north. Winters can be cold, especially in the south, where it sometimes snows, but soils never become frozen. Most soils of the Pampas were developed from loess-like sediments and are mainly Mollisols. From east to west, soils are mainly Argiudolls, Hapludolls, and Haplustolls, and in some localized areas Natraquolls. Other less representative soils are Alfisols, Vertisols, and Entisols (Lavado and Taboada 2009). The Pampas is…

Nitrogen Dynamics and Losses in Direct‐Drilled Maize Systems

Abstract The knowledge of nitrogen (N) losses in direct‐drilling agrosystems is essential to develop strategies to increase fertilizer efficiency and to minimize environmental damage. The objectives were i) to quantify the magnitude of N volatilization and leaching simultaneously as affected by different urea fertilization rates and ii) to evaluate the capacity of these specific plant–soil systems to act as a buffer to prevent nitrate leaching. Two experiments were conducted during 2001/02 and 2002/03 growing seasons in Alberti, Argentina. The crop was direct‐drilled maize and the soil a Typic Argiudoll. Ammonia losses, N uptake by crop at flowering and harvest, grain yield, N in previous crop residues, and soil nitrate content up to 2‐m depths were determined. Nitrogen availability, soil nitrate (NO3)‐N up to 1 m plus fertilizer N, was linearly and highly associated with crop N uptake at flowering (R2=0.93, P<0.01) and at harvest (R2=0.852, P<0.01). Around 17.5% of fertilizer N was lost by volatilization in 10 days. The obtained values of residual nitrate N up to the 150‐cm depth were associated (R2=0.960, P<0.001) with those predicted by the nitrate leaching and economic analysis package (NLEAP) model. Maize in the direct‐drilling system was able to cycle N from the previous crop residues, N from soil organic matter, and N from fertilizers with few losses.

Maize and cover crop sequence in the Pampas: Effect of fertilization and water stress on the fate of nitrogen

Cover crops are well known for their positive effects on erosion processes, soil organic matter, soil physical properties, weed populations and nitrate (NO3) leaching. In this work, we evaluated the fate of nitrogen (N) from fertilizer in maize (Zea mays L.) and then in ryegrass (Lolium multiflorum) as cover crop, in the conditions of the Argentine Pampas. To this end, a field experiment was carried out at the School of Agriculture, University of Buenos Aires, Argentina (34°36′ S, 58°29′ W). The design of the experiment was factorial with three replications. We applied to maize two levels of N (0 and 140 kg N ha−1 [125 lb N ac−1] ammonium nitrate target with 15N) and two levels of water (50% and 100% of crop evapotranspiration). 15N was determined in both the soil and plants. Maize plants and the soil organic fraction were the main sinks of fertilizer N, depending on the water treatment. The N from fertilizer remaining as NO3 in the soil (0 to 1.5 m [0 to 4.92 ft] depth) at maize harvest was 8% in plots subjected to water stress compared to 3% in the nonstressed. Nitrogen losses due to volatilization were minor. Total N (soil and fertilizer) accumulated in ryegrass tissues plus NO3 remaining in the soil were higher in cover crop plots than in bare soil (130 versus 51 kg N ha−1 [116 versus 45.5 lb N ac−1]). The N in the soil organic matter originating from fertilizer significantly decreased between maize harvest and cover crop harvest. This soil organic N that originated from fertilizer mineralized at high rate (around 47% in six months), suggesting it was in more labile. This mineralized N can be subjected to potential losses during following months.