H. S. Steinbach

PREDICTIONS OF AVAILABLE NITROGEN CONTENT IN SOIL PROFILE DEPTH USING AVAILABLE NITROGEN CONCENTRATION IN SURFACE LAYER

The Rolling and Flat Pampas are vast plains which contribute with more than half of the Argentine wheat production. In the 80s three extensive studies were preformed in these regions, which determined nitrate content in the 0–20, 20–40, and 40–60 cm soil layers, comprising a wide range of soil, climatic and cultural variables. More recently, we determined the mineral-N (N) content at 0–30 and 30–60 cm depths, in a set of farmers plots under different tillage systems and previous crop. These datasets were used in order to establish simple equations to predict N availability in the 0–60 cm stratum, from the N availability in the upper layer. Nitrate content at wheat presowing time presented a clear stratification pattern with depth. For the fist dataset, strong relationships were obtained between the nitrate content at different soil depths, with previous crops of corn, sunflower or sorghum (R2=0.52 to 0.90, P<0.05), but low adjustments were obtained for soybean. In the second set of data, mineral-N measured in the 0–30 and 30–60 cm layers were also linearly correlated, for each tillage treatment (plow, disk and no-till) and previous crop (R2>0.62). Two general equations were obtained that relates N availability in the upper layer with the availability in the 0–60 cm layer (R2=0.89, P<0.001), comprising a wide range of management and environmental conditions. As N fertilizer recommendations in these Pampean Regions required soil nitrate content to a depth of 60 cm, close predictions of N availability in the this stratum from the upper layer can facilitate sampling and extent the use of the diagnosis methodologies by farmers.

Association between soil organic matter and wheat yield in Humid Pampa of Argentina

The Rolling and Flat Pampas are vast plains located in Argentina. Wheat is one of the most economically important crops of these regions. Two extensive studies have been preformed to evaluate the effects of nitrogen fertilization on wheat yield at field scale. We pooled these published data to establish relationships between wheat yield and soil and climate variables under a wide range of soils and management conditions. Total soil carbon was the variable more associated with yield (r2=0.25). The increase in grain production expected between soils with low and high carbon levels rounded 2,200 kg ha− 1. A multivariate model which included carbon in the light fraction, potential mineralizaable nitrogen, available mineral nitrogen, and rainfall was obtained, explaining 50% of wheat yield variability. These results highlight the importance of organic matter on grain production in the Humid Pampas. This effect can be due to the role of organic soil components as source of nutrients for crops.

Comparison of nitrogen fertilizer demand for wheat production between humid and semi-arid portions of the Argentinean Pampas using a mass balance method

The Argentinean Pampa is an important grain production region in which nitrogen (N) availability restricts wheat (Triticum aestivum L.) yield. We performed 46 experiments in the Semi-arid Pampa for evaluating soil N supplying capacity using a mass balance approach. The information generated was combined with published results from 58 experiments performed in the Humid Pampa. Average rainfall was 50% lower under semi-arid conditions and soils had half of the clay + silt and total N contents than those of humid environments. Wheat yield under humid scenarios doubled the yield attained under semi-arid ones, and N and rainfall use efficiencies were also higher. A model could be fitted with good performance for estimating N-supplying capacity from mineral and organic soil pools (R2 = 0.53–0.93), absorbed N (R2 = 0.70) and yield (R2 = 0.57). This methodology can be used for estimating fertilizer needs under defined climate- and site-specific scenarios. For the average yields, rainfall and soil conditions of the experimental networks, targeted N supply (soil mineral + fertilizer N) was estimated as 160 kg N ha−1 in the Humid Pampa and 50 kg N ha−1 in the Semi-arid Pampa. Current N rates applied by farmers need to be increased under humid conditions and overfertilization occurs under semi-arid ones.