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Fil: Beltran, Marcelo Javier. Instituto Nacional de Tecnologia Agropecuaria (INTA). Instituto de Suelos; Argentina

It remains uncertain how oat (Avena sativa L.) and hairy vetch (Vicia villosa Roth.) impact both nitrogen (N) and sulfur (S) recycling in cover crop-maize (Zea mays L.) systems as well as N and S diagnostic methods in maize. Field trials were conducted at three sites in the southeastern Argentinean Pampas to evaluate the effect of oat, hairy vetch, and bare fallow combined with four N and S fertilization treatments (unfertilized, N-, S-, and NS-fertilized) on maize. Soil N and S content at maize sowing, chlorophyll meter reading (CMR) at silking, and grain yield were determined. Overall, soil NO3−-N content (0–60 cm) at maize sowing was hairy vetch > bare fallow > oat, while SO4−2-S content was hairy vetch > bare fallow = oat. Maize yield response to N was predicted from soil NO3−-N content (R2 = 0.80). The CMR was negatively correlated with cover crop residue quality (carbon (C)/N and C/S ratios). Also, CMR accurately predicted variations in maize grain yield. In the unfertilized treatment, maize yield was hairy vetch > bare fallow > oat, in two of the three sites. There was no yield response to N or S with hairy vetch. Oat and hairy vetch differentially affected N and S recycling in cover crop-maize cropping systems. Soil NO3−-N and SO4−2-S content at maize sowing combined with CMR are reliable diagnostic tools to assess maize N and S, allowing for sustainable fertilization management.

In the last decades, there has been a tendency towards sustainable agriculture. Following this trend, edaphic fungi as Trichoderma and arbuscular mycorrhizal fungi (AMF) could increase plant growth contributing to diminish agricultural chemical supply. However, little information exists in current research regarding the possible effects of alternative practices to soybean monoculture systems on fungal groups that could contribute to plant health and/or productivity. Thus, our objective was to assess changes in the abundance and diversity of indigenous AMF and Trichoderma from a long-term field experiment located in the Argentinean Pampas, in order to test the effect of alternative practices to soybean monoculture. The fungal ability to promote the growth of crops, such us tomato plant was also tested. Soil samples were collected from a soybean monoculture system (Sb), a system including cover crop (Avena sativa) followed by soybean (CC/Sb) and a system including rotations (rot) of SoybeanMaize-Wheat crops CC/Sb-rot, M-rot and W-rot, respectively. Highest AMF and Trichoderma abundance was found at W-rot and M-rot systems, and highest AMF diversity was found at W-rot and CC systems. Furthermore, highest mycorrhizal colonization was found at CC/Sb and W-rot systems. Inoculated plants with single AMF consortium or with Trichoderma strains showed significant increases in comparison with the control. Dual inoculation increased tomato plant growth as compared to the control, and evidence of synergism was found by increases in shoot and root growth. Our results show that dual inoculation with indigenous AMF and Trichoderma from alternative crop systems to soybean monoculture could play an important role in tomato plant growth. This information could be useful to decrease production costs and environmental impacts.

Soya bean (Glycine max (L.) Merr.) monoculture can lead to a decrease in labile fractions of soil organic carbon (SOC). This study sought to evaluate the effects of cover crops (CC), application of fertilizer, and crop rotation on SOC, particulate organic carbon (POC), and soil carbon input in soya bean‐based crop sequences under a no‐till cropping system in the Argentinean Humid Pampas. Five crop sequences at two sites differing in initial SOC were evaluated: continuous soya bean (Sb), continuous soya bean fertilized with phosphorus (P) and sulphur (S) (Sbf), grass CC / PS‐fertilized soya bean (CC/Sbf), nitrogen (N)‐fertilized CC / PS‐fertilized soya bean (CCf/Sbf) and NPS‐fertilized crop rotation with high intensification sequence index (ISI) (Rot). At 0–5 cm, SOC and POC were higher (p

Maize (Zea mays L.) is one of the most susceptible crops to zinc (Zn) deficiency. However, in much of the world, soil Zn tests are poorly calibrated, and thus determining a critical soil test, level for Zn is challenging. The objectives of this study were to: (i) produce a field calibration of the Zn Mehlich-3 (M3-Zn) method for predicting maize grain yield response to Zn fertilizer application, (ii) compare the capacity of DTPA extractable Zn (DTPA-Zn) with M3-Zn for predicting the response of maize yield to Zn fertilizer, (iii) determine whether inclusion of soil pH, organic matter (SOM) and extractable phosphorus in a M3-Zn model improves its predictive capacity and (iv) evaluate an economic approach for determining soil Zn thresholds. We conducted 55 field experiments covering a wide range of edaphic and climatic conditions. Maize responded to Zn fertilizer in 29% of the trials. The capacity of M3-Zn and DTPA-Zn to predict relative yield of maize was similar. Inclusion of other soil variables (pH, extractable phosphorus and SOM) did not or only slightly improve the prediction of M3-Zn. Based on the relationship between M3-Zn and DTPA-Zn (R2 = 0.89), one test can be predicted from the other without affecting the calibration. The M3-Zn 'economic threshold' ranged from 0.98 to 2.79 mg kg−1, while for DTPA-Zn it varied from 0.41 to 1.61 mg kg−1. The broad range of economic thresholds shows that differences in maize productivity and grain price between regions and seasons make establishing a single Zn threshold for all economic-productive situations inappropriate. Fil: Martínez Cuesta, Nicolás. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Wyngaard, Nicolás. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Innovación Para la Producción Agropecuaria y El Desarrollo Sostenible. - Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Buenos Aires Sur. Estacion Experimental Agropecuaria Balcarce. Instituto de Innovación Para la Producción Agropecuaria y El Desarrollo Sostenible.; Argentina Fil: Sainz Rozas, Hernan Rene. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Reussi Calvo, Nahuel Ignacio. Laboratorio de Analisis de Suelos Fertilab; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Carciochi, Walter Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Eyherabide, Mercedes. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Innovación Para la Producción Agropecuaria y El Desarrollo Sostenible. - Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Buenos Aires Sur. Estacion Experimental Agropecuaria Balcarce. Instituto de Innovación Para la Producción Agropecuaria y El Desarrollo Sostenible.; Argentina Fil: Colazo, Juan Cruz. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Barraco, Mariano Manuel. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Guertal, Elizabeth A.. Auburn University.; Estados Unidos Fil: Barbieri, Pablo Andres. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Innovación Para la Producción Agropecuaria y El Desarrollo Sostenible. - Instituto Nacional de Tecnologia Agropecuaria. Centro Regional Buenos Aires Sur. Estacion Experimental Agropecuaria Balcarce. Instituto de Innovación Para la Producción Agropecuaria y El Desarrollo Sostenible.; Argentina

Soybean (Glycine max (L.) Merr.) monoculture contributes to soil degradation. Intensification of soybean-based sequences through polyculture, cover crops (CC), and crop fertilization can enhance soil physical quality and help mitigate its degradation. We assessed the effect of intensification practices in cropping sequences with soybean predominance on soil physical quality indicators in contrasting soils. Treatments included soybean monoculture with and without phosphorus (P) and sulfur (S) fertilization, CC/PS-fertilized soybean, nitrogen (N)-fertilized CC/PS-fertilized soybean and NPS-fertilized crop rotation including wheat, corn, soybean and CC. Four long-term experiments (10 yr) were established in sites with contrasting edaphoclimatic conditions, and initial soil organic carbon (SOC), where we evaluated bulk density (BD) and aggregate stability (AS). The BD was mostly unaffected by treatments, whereas AS responded to intensification practices at all sites, increasing over 50% as compared with soybean monoculture. Differences in BD and AS among sites were mostly explained by soil texture and initial SOC. On the contrary, AS differences among treatments were not driven by texture, but by the soil degradation at the beginning of the experiments (calculated as the ratio between SOC when experiments were established and the SOC of pristine soil). Therefore, regardless of soil texture, more degraded soils responded to a greater extent to intensification practices in soybean-based rotations.

The most widely used approach for prescribing fertilizer nitrogen (N) recommendations in maize (Zea Mays L.) in Argentina is based on the relationship between grain yield and the available N (kg N ha−1), calculated as the sum of pre-plant soil NO3--N at 0−60 cm depth (PPNT) plus fertilizer N (Nf). However, combining covariates related to crop N demand and soil N supply at a large national scale remains unexplored for this model. The aim of this work was to identify yield response patterns associated to yield environment (crop N demand driver) and soil texture (soil N supply driver). A database of 788 experiments (1980−2016) was gathered and analyzed combining quadratic-plateau regression models with bootstrapping to address expected values and variability on response parameters and derived quantities. The database was divided into three groups according to soil texture (fine, medium and coarse) and five groups based on the empirical distribution of maximum observed yields (from Very-Low = 13.1 Mg ha−1) resulting in fifteen groups. The best model included both, attainable yield environment and soil texture. The yield environment mainly modified the agronomic optimum available N (AONav), with an expected increase rate of ca. 21.4 kg N Mg attainable yield−1, regardless of the soil texture. In Very-Low yield environments, AONav was characterized by a high level of uncertainty, related to a poor fit of the N response model. To a lesser extent, soil texture modified the response curvature but not the AONav, mainly by modifying the response rate to N (Fine > Medium > Coarse), and the N use efficiencies. Considering hypothetical PPNT levels from 40 to 120 kg N ha−1, the expected agronomic efficiency (AENf) at the AONav varied from 7 to 31, and 9–29 kg yield response kg fertilizer N (Nf)−1, for Low and Very-High yield environments, respectively. Similarly, the expected partial factor productivity (PFPNf) at the AONav ranged from 62 to 158, and 55–99 kg yield kg Nf−1, for the same yield environments. These results highlight the importance of combining attainable yield environment and soil texture metadata for refining N fertilizer recommendations. Acknowledging the still low N fertilizer use in Argentina, space exists to safely increasing N fertilizer rates, steering the historical soil N mining profile to a more sustainable agro-environmental scenario in the Pampas.

Nitrogen (N) and sulfur (S) define crops productivity, and are currently deficient in most agricultural soils. In agricultural systems, management practices can affect N and S organic pools (Norg and Sorg, respectively). The objective of our study was to assess how intensification practices [use of grasses as cover crops (CC) and/or fertilization] affect Norg and Sorg, anaerobic N (Nan), and carbon (C)/N and C/S ratios as compared with soybean [Glycine max (L.) Merr.] monoculture, in soils under no tillage, with contrasting edaphoclimatic conditions. The experiment was carried out in four long term experiments (> 10 yr), where four treatments were evaluated: control (soybean monoculture (Sb)), soybean monoculture fertilized with phosphorus (P) and S (Sbf), CC / soybean (Sb/CC), and CC / P + S-fertilized soybean (Sbf/CC). The inclusion of CC increased Norg and Sorg as compared to Sb (from 20 % to 30 % for Norg, and from 16 % to 18 % for Sorg) at 0−5 cm.The magnitude of the effect of CC increase on Norg was positively associated with temperature, clay + silt and crops dry matter, whereas the increase in Sorg was positively associated with precipitation, clay + silt, and crops dry matter. The Nan improved over 50 % due to the inclusion of CC. Also, at two sites P + S-fertilization improved Nan (37 %) as compared with Sb. Our results suggest that intensification practices (CC and PS-fertilization) result in an accumulation of readily available N and S organic fractions, which can have a potential positive impact on the productivity of other crops in the cropping sequence. However, as previously mentioned, the magnitude of that positive effect will depend on the edaphoclimatic characteristics of each site.

Current zinc (Zn) diagnostic methods for corn (Zea mays L.) are often based on soil DTPA (diethylenetriamine-pentaacetic acid) extractable Zn (DTPA-Zn). However, calibration of the DTPA-Zn test may be influenced by other soil properties such as pH, organic matter (SOM) and available Bray-P (PBray-1). Our objective was to assess the contribution of soil properties to a DTPA-Zn model used to predict corn response to Zn fertilization. We conducted 64 field trials with two Zn-fertilization treatments: With and without Zn fertilization. In all sites, we measured SOM, PBray-1, pH, and DTPA-Zn at 0-to 20-cm depth before sowing. Yield difference between Zn-fertilized and unfertilized treatments (Ydifference) was significant in 33% of the experimental site-years. In responsive site-years, the average Ydifference was 0.98 Mg ha-1 (11.4%). Soil organic matter was the only property that was a significant addition to the DTPA-Zn model for predicting the corn relative yield (Model R2 including SOM = 0.27). However, the improvement was nominal (Partial R2 of SOM = 0.06). Use of DTPA-Zn alone was suitable to discriminate Zn responsiveness among site-years based on the Ydifference by correctly diagnosing 81% of the outcomes. We determined three soil DPTA-Zn ranges with different probability of resulting in a Ydifference greater than zero when fertilized with Zn: High (1.3 mg kg-1). These soil-test-based Zn recommendations improve the identification of Zn-deficient soils allowing prevention of yield loss from Zn deficiency and more rational use of Zn fertilizers. Fil: Barbieri, Pablo Andres. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina Fil: Sainz Rozas, Hernan Rene. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Wyngaard, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Eyherabide, Mercedes. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Reussi Calvo, Nahuel Ignacio. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Correndo, Adrián A.. International Plant Nutrition Institute; Argentina Fil: Barbagelata, Pedro A.. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Espósito Goya, Gabriel P.. Universidad Nacional de Río Cuarto; Argentina Fil: Colazo, Juan Cruz. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria San Luis; Argentina Fil: Echeverria, Hernan Eduardo. Instituto Nacional de Tecnología Agropecuaria; Argentina

The challenge to increase agricultural production with a minimum environmental impact requires to reach the maximum efficiency in the capture and use of resources such as photosynthetically active radiation (PAR), water, and nitrogen (N). Such requisites are encompassed in the ecological intensification (EI) concept. The aims of this work were to evaluate at a crop sequence level: i) crops yields, ii) water and radiation productivity and its components, i.e. resource capture and resource use efficiency, and iii) partial factor productivity of applied N (PFPN), partial nutrient balance for N (PNB), N uptake and N utilization efficiency of a two-year, three-crop sequence (wheat [Triticum aestivum L.]/soybean [Glycine max (L.) Merr.] double crop – maize [Zea mays L.]) carried-out under EI principles in comparison with the same crop sequence under current farmer practices (FP) in two contrasting locations of the Argentinean Pampas, i.e. Paraná (-31°50′; -60°31′) at the northern Pampas and Balcarce (-37°45′ -58°18′) at the southern Pampas. Experiments were carried-out during four consecutive years, covering two complete cycles of the crop sequence. For the accumulated grain production of the crop sequence, EI management outyielded FP from 13 to 42%, depending on environmental conditions. Maize yield accounted for most of the variation (41–64%) of the accumulated grain yield of crop sequence, whether in EI as in FP. Average grain yield differences between EI and FP treatments were 274 g m −2 for maize, 69 g m −2 for wheat and -2 g m −2 for soybean. Water and radiation productivities of the sequence were higher in EI than in FP (26% for water and 17% for radiation; P < 0.0001), mainly because of increases in resource use efficiencies. EI reduced partial factor productivity of applied N, but improved partial nutrient balance for N as compared with FP. These reductions in partial factor productivity of applied N were less than proportional than the increases in N rate. Moreover, in spite of the higher N rate in EI respect to FP, N utilization efficiency (N ut E), i.e. grain per unit N uptake, was higher across all situations in EI. Our results showed that the challenge to obtain high grain yields by increasing N rate in a medium-input system could be achieved even with an increase in N ut E. Grain yields improvements, and increases in radiation and water productivity were reached by applying a set of agronomic practices that included improved genetics, crop and fertilizer N management englobed under EI concept. Fil: Caviglia, Octavio Pedro. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina. Universidad Nacional de Entre Ríos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Rizzalli, Roberto Héctor. Universidad Nacional de Mar del Plata; Argentina Fil: Monzon, Juan Pablo. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Garcia, Fernando Oscar. Universidad Nacional de Mar del Plata; Argentina. International Plant Nutrition Institute Latinoamérica; Argentina Fil: Melchiori, Ricardo José Miguel. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Martinez, J.J.. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Cerrudo, Anibal Alejandro. Instituto Nacional de Tecnología Agropecuaria; Argentina. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Irigoyen, Andrea Inés. Universidad Nacional de Mar del Plata; Argentina Fil: Barbieri, Pablo Andres. Universidad Nacional de Mar del Plata; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Van Opstal, Natalia. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Andrade, Fernando Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina

In environments where continuous agriculture leads to soil organic carbon (SOC) depletion, intensification practices (i.e. polyculture, cover crops (CC), and crop fertilization) have been suggested as strategies to improve crop residue inputs which, in turn, can increase SOC storage. However, SOC dynamics are regulated by a complex interplay of climatic and soil conditions. The objective of our study was to assess how intensification practices affect SOC, particulate organic carbon (POC) and SOC stratification ratio (SRSOC) as compared to soybean [Glycine max (L.) Merr.] monoculture, in soils with contrasting soil properties and climate. The experiment was carried out in four long term experiments (>10 yr) located in areas with contrasting environments. The surface soil textures ranged from sandy-loam to silty-clay and clay-loam, initial SOC (0–20 cm) from 34.5 to 67.8 Mg ha−1, mean air temperature: 14.0–18.9 °C, annual precipitation: 719.8–886.1 mm. Five treatments were evaluated: soybean monoculture (SB), soybean monoculture fertilized with phosphorus (P) and sulfur (S) (SBPS), CC/PS-fertilized soybean (SBPS/CC), nitrogen (N)-fertilized CC/PS-fertilized soybean (SBPS/CCN) and NPS-fertilized crop rotation (ROTNPS). Intensification of crop sequences (SBPS/CC, SBPS/CCN and/or ROTNPS) increased SOC and POC at 0–5 cm and in SRSOC in most sites as compared to SB. All treatments showed SOC depletion as compared to the beginning of the experiment. However, the magnitude of SOC lost during 10 years was 26–65% lower when intensified crop sequences were applied as compared with SB. Carbon input and environment characteristics influenced the impact of intensification practices on the analyzed variables. However, this effect was mostly associated with the ratio between SOC at the beginning of the experiment and the SOC of pristine soil (degradation status). The intensification practices evaluated were not sufficient to reverse the tendency of agricultural soils to lose SOC, but they slowed the rate of this degradation process.

We evaluated the influence of the termination dates of a winter cover crop on (i) soil water availability during soybean (Glycine max L. (Merr)) growing season, (ii) soybean evapotranspiration (ET) and iii) water productivity in soybean (WP = Grain yield/ET) in a humid environment (i.e., 50 % of years with annual rainfall ≥900 mm). Experiments were carried out at Balcarce, Argentina during two growing seasons. Treatments included (i) soybean monoculture, (ii) soybean following a cover crop with an early termination date, and (iii) soybean following a cover crop with a delayed termination date (∼25 days later than the early one). Oat (Avena sativa L.) was used as a cover crop. Soil water content was measured with a neutron probe from cover crop sowing to soybean physiological maturity, and soybean ET was calculated by means of a soil water balance. Cover crop shoot biomass was determined immediately before termination dates and soybean grain yield was quantified at physiological maturity. Cover crops reduced soil available water (SAW) at cover crops termination date from 18 to 23 mm at early and delayed termination dates, respectively; and reductions were mostly evident in the upper 40 cm of the soil profile. Termination delays of around 25 days increased 60 % cover crops shoot biomass production, and promoted larger SAW reductions at termination date. However, cover crops had little impact on SAW during soybean growing season and they did not influence soybean grain yield. Moreover, our findings evidenced that in this humid environment (i) soybean ET was reduced between 12 and 17 mm following a cover crop, (ii) larger soybean ET reductions were associated with larger cover crops shoot biomass production, and (iii) WP in soybean was slightly improved (4–10%) by the inclusion of a cover crop.

Nitrogen (N) rate increases used by many farmers produce a reduced or null effect on N recovery efficiency (RE) by crops. Therefore, management practices to reduce N losses and increase RE are necessary. Co-polymer maleic itaconic acid (NSN) have become available for use with urea and has shown potential in reducing N losses. The objective of this study was to evaluate the effectiveness of urea treated with NSN on grain yield and RE in a no-till corn. A field experiment was carried out at Balcarce, Argentina over three years, evaluated treatments were urea and urea + NSN at 120 N kg ha&minus, 1, and additional 0 N treatment was included. Urea + NSN was effective to reduce total ammonia volatilization losses, and the average of two years were 1.4 (1.1% to N applied) and 8.7 kg ha&minus, 1 (7.2% to N applied) for urea + NSN and urea, respectively. However, while grain yield and N grain removal were not affected by urea + NSN, the N rate significantly increased grain yield and N grain removal. Nitrogen recovery efficiency was not affected by urea + NSN, RE (average of three years) was 29.0% and 27.8% for urea and urea + NSN, respectively. In conclusion, there was no advantage of using urea treated with NSN in no-till corn overgrain yield, N grain removal, or RE.

In the Southeastern region of Buenos Aires province, soybean monoculture has led to a decline in soil organic matter (SOM) levels in soil, mostly the labile fractions. The reduction of SOM has a negative impact on the soil environment. Cover crops (CC) constitute an alternative to maintain or improve SOM levels. The aim of this study was to determine the effect of oat as CC on (a) the SOM dynamics and (b) the availability of macro- and micronutrients in a representative soil of the Southeastern region of Buenos Aires province. Total organic carbon (TOC) and nitrogen (TON), as well as their labile and mineral-associated fractions, and macro- and micronutrient availability were determined. The treatments were soybean monoculture with and without oat as cover crop. The increases in SOC and TON were 22.7% and 11%, respectively, when CC was included to the soybean monoculture. These increases were observed mostly in the labile fractions, with increases of 61.3 and 38.7% for the particulate coarse organic carbon (PCOf) and particulate fine organic carbon (PCOf), respectively, and 79.2% for the particulate coarse organic nitrogen (NOPg). Regarding the nutrients, an increase of 47.6% was observed in manganese (Mn) in the first 5 cm of soil depth, and a decrease in phosphorous (P) availability in the same soil layer due to its consumption and retention by CC. It can be conclude that CC presented a surface soil effect on the dynamic of SOM, increasing C, N, and available Mn contents, but decreasing soil P availability. Fil: Beltrán, Marcelo Javier. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Sainz Rozas, Hernan Rene. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina Fil: Galantini, Juan Alberto. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina Fil: Romaniuk, Romina Ingrid. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina Fil: Barbieri, Pablo Andres. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires; Argentina

A correct determination of nitrogen (N) fertilization thresholds in wheat that is based on objective yield produces efficient use of this nutrient. Nitrogen fertilization recommendations for traditional wheat require determination of nitrate (NO3 −)-N availability at 60 cm deep at planting time. However, this methodology is complicated, expensive, and time-consuming; thus, the determination of NO3 −-N level at a lesser depth and at a different time would be desirable. The goals of this work were to determine available N in soil thresholds for traditional and French germplasm wheats and the feasibility of diagnosing N requirements by measuring NO3 −-N at 40 cm deep, at planting or tillering times, in the southeastern Pampas. The experiments were factorial combinations of N rates and fertilization times (planting and tillering) at different sites and years during 2002–2006. Nitrogen fertilization significantly increased grain yield and protein content. French varieties presented greater grain yield (23%), l...

Nitrogen (N) fertilization is an important management practice to increased grain yield; however, it is imperative to increase nitrogen use efficiency (NUE) in order to diminish risks of environmental pollution. The objective of this study was to determine the effect of fertilization times on wheat grain yield, grain N accumulation and grain N recovery efficiency (RE) in different sites and years at the south-eastern wheat belt of the Pampas. The experiments were a factorial combination of N rates and fertilization times (sowing and tillering). Grain yield ranged from 1600 to 7900 kg ha-1 and fertilization at tillering increased grain yield compared with fertilization at sowing (5465 vs. 5110 kg ha-1), similar behavior was observed for grain N accumulation (95 vs. 86 kg ha-1) and RE (0.41 vs. 0.32). Predicted grain yield by CERES-Wheat model for different N rates and fertilization times was correlated with observed grain yield (r2 = 0.71). While fertilization at tillering significantly increased grain yield, CERES-Wheat model estimated nitrate leaching losses that ranged from 12 to 62 kg N ha-1 and from 7 to 16 kg N ha-1 for fertilization at sowing and tillering, respectively. However, denitrification losses ranged from 1.2 to 3.9 and from 0.5 to 2.4 kg N ha-1 for fertilization at sowing and tillering, respectively. Leaching losses for fertilization at sowing are a consequence of water excess early in the growing season and would be the main N loss factor. Therefore, N application at tillering is an appropriate strategy to improve NUE in the south-eastern wheat belt of the Pampas. Key words: Wheat, fertilization time, nitrogen use efficiency, N losses, CERES-Wheat

Efficient use ofN in plant production is an essential goal in crop management. An experiment was performed at INTA Balcarce, Argentina during 3-yr to evaluate the effect of row spacing and N level on nitrogen use efficiency (NUE) in no-till (NT) irrigated maize (Zea mays L.). Treatments consisted of a factorial combination of row width (70, 52 and 35 cm) and N rates (0 to 180 kg N ha -1 ). Nitrogen rate and narrow rows increased total dry matter (DM), grain yield, and N accumulation. Relative responses to narrow rows decreased as N availability increased. The NUE decreased with N rate and increased with narrow row spacing. Narrow rows increased NUE by 12 and 15% expressed as DM or grain yield per unit of available N, respectively. Physiological efficiency decreased with N rate and was not affected by row spacing. Recovery efficiency (RE) decreased with increasing N rate, and increased for the narrow row spacings. The effect of narrow rows on RE decreased as N availability increased. Narrow rows increased NUE largely as a result of increased RE. These increments in RE could contribute to increase the profitability of maize production and to diminish the risk of environmental pollution.

A presidedress soil nitrate test (PSNT) can be used to evaluate preplant N applications as a complementary method to N budget in maize (Zea mays L.) under different management practices. Narrow rows have shown increased N accumulation and recovery efficiency by maize, and therefore soil NO 3 - -N critical concentration (CC) for maximum yield could be lower than in conventional row spacing. An experiment was performed at Balcarce (Argentina) in 1996-1997, 1999-2000, and 2000-2001 to evaluate the PSNT for irrigated no-till (NT) maize with different row spacings (70, 52, and 35 cm) and N rates (0, 90, 140, and 180 kg N ha -1 ). Soil samples were collected to a 30-cm and 30- to 60-cm depth when maize was at the six-leaf stage (V6). Grain yield was significantly increased by narrow rows mainly at low N availability. Relative yield was highly associated (r 2 = 0.73 and 0.68) with soil NO 3 - -N concentration (0-30 cm) at V6 for conventional and narrow rows, respectively. Soil NO 3 - -N concentration for maximum yield (95%) was greater for conventional row spacing (22 mg kg -1 ) compared with narrow rows (17 mg kg -1 ). The reliability of the PSNT (r 2 ) did not improve when sampling was done up to a 60-cm depth. These results confirm the hypothesis that the NO 3 - -N CC determined for the PSNT is lower for maize crops growing in narrow rows than conventional row spacing. Narrow rows maize is a simple management practice that could contribute to enhancing system sustainability.

The objective of this work was to evaluate if soil mineralizable N under anaerobic conditions (Nan) improves the reliability of preplant soil nitrate test (PPNT) and presidedress soil nitrate test (PSNT). The study was conducted under no-tillage (NT) in the southeastern Buenos Aires province, Argentina, in 26 site-years. In some site-years treatments were fixed N rates (0, 70, 140, and 210 kg ha -1 or 0, 60, 120, 180, and 240 kg ha -1 ) applied at planting, whereas in others site-years N rates were determined by adding N to lead targets of N supply up to 120, 160, and 200 kg N ha -1 . When sites were not separated by Nan, relative yield (RY) correlated with PPNT (r 2 = 0.37) and reliability of PPNT did not increase when sites were separated by low ( 48 mg kg -1 ). A high relationship between RY and PSNT (r 2 = 0.56) was determined. However, when sites were separated by Nan, reliability of PSNT increased, mainly for sites with low Nan (r 2 = 0.68 and 0.44 for sites with low and high Nan, respectively). Critical PSNT values for 94% of RY were 75 and 90 kg N ha -1 for sites with high and low Nan, respectively. The results show that PSNT was a better diagnostic method for maize (Zea mays L.) than PPNT. However, the separation of sites by its N mineralization capacity increased reliability of PSNT by indicating a lower N requirement to reach 94% of RY, decreasing the risk ofoverfertilization, an important feature from economical and environmental standpoints.

Crop production in Argentina has significantly increased over the past few years; this increase was consequence of better management practices which included P and N fertilization and, occasionally, S fertilization. Commonly used rates, however, are not sufficient to balance nutrients export in grain crops. This situation is particularly negative for meso-nutrients (Ca+2 and Mg+2) because they are not normally applied by farmers. The objective of this study was to determine the effect of lime over four years period on soybean, one year period on wheat and on a one year double cropped wheat/soybean combination on no-till. The experimental design was a randomized complete blocks design with three replications and two combinations of lime (with and without). Results showed that lime application significantly increased soil pH, exchangeable Ca+2 content, and therefore, base saturation and Ca+2 saturation in cation exchangeable capacity (CEC). As average growing seasons, the relative increments due to lime application were 8, 22, 18, and 20% for pH, soil exchangeable Ca+2 content, base saturation and Ca+2 saturation in CEC, respectively. Results showed that soil bulk density and penetration resistance were not affected by lime application. Soil structure stability was significantly affected by lime application. Wheat grain yield was not affected by lime, but soybean grain yield was significantly increased by lime (7% average across year). Cumulative grain yield was significantly increased by lime application indicating that the benefits of liming were cumulative over time (27,556 vs 28,629 kg ha−1 for lime and no lime, respectively). Increments in relative grain yield were not associated with soil pH in both crops; however, significant relationships were determined between relative soybean grain yield and soil Ca+2 content, base saturation and Ca+2 content in CEC. A soil Ca+2 critical concentration of 12.4 meq 100 g−1 was determined to obtain 95% of relative soybean grain yield. The study concluded that soil Ca+2 content would limit soybean grain yield as a consequence of cation unbalance in intensive agriculture soil. Fil: Barbieri, Pablo Andres. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Echeverria, Hernan Eduardo. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sainz Rozas, Hernan Rene. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Martínez, Juan P.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina

The response of grain yield to narrow rows can be analyzed in terms of the effect on the amount of radiation intercepted by the crops. The objective of this work was to study the effect of row spacing on grain yield and radiation interception (RI) during the critical period for grain set in three crop species. Ten experiments were conducted with maize (Zea mays L.), sunflower (Helianthus annuus L.), or soybean [Glycine max (L.) Merr.] under irrigation or under dryland conditions without severe drought during flowering and grain filling. The treatments consisted of two row distances combined with other factors such as plant density, cultivar, defoliation, etc. Grain yield responses to decrease distance between rows were inversely proportional to RI achieved with the wide-row control treatment during the critical period for grain number determination (r 2 = 0.62, 0.54, and 0.86 for maize, soybean, and sunflower, respectively). Moreover, when row spacing was reduced, grain yield increases and RI increases during the critical periods for grain set were significantly and directly correlated in the three crop species (r 2 = 0.71, 0.64, and 0.94 for maize, soybean, and sunflower, respectively). For the conditions of these experiments, grain yield increase in response to narrow rows was closely related to the improvement in light interception during the critical period for grain set.

No-till (NT) affects dynamics of phosphorus (P) applied. Wheat response to P fertilization can be affected by available soil P, grain yield, placement, rate, and timing of fertilization. Furthermore, mycorrhizal associations could contribute to improving plant P uptake. Three experiments were used to evaluate P rate (0, 25, and 50 kg P ha−1) and fertilizer placement (broadcasted or deep-banded) effects in NT wheat on P recovery efficiency (PRE) yield and arbuscular mycorrhizal colonization (AMC) which was assessed in one experiment. Fertilization increased dry matter (DM) and accumulated P. Broadcasted P produced lower P accumulation than deep-banded P only at tillering. Phosphorus rate decreased PRE, and placement method did not affect it. Grain yield response was increased by P rate (857 and 1805 kg ha−1 for 25 and 50 kg P ha−1, resp.) and was not affected by placement method (4774 and 5333 kg ha−1 for broadcasted and deep-banded, resp.). Deep-banded P depressed root AMC compared with broadcast applications. Highest AMC in P broadcasted treatments could help to explain the lack of differences between placement methods. These results indicate that Mollisol have low P retention capacity. Therefore, broadcasted P could be used as an alternative of fertilizer management for NT wheat. Fil: Barbieri, Pablo Andres. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires. Estación Experimental Agropecuaria Balcarce; Argentina Fil: Sainz Rozas, Hernan Rene. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires. Estación Experimental Agropecuaria Balcarce; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Covacevich, Fernanda. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones en Biodiversidad y Biotecnología; Argentina. Fundación para Investigaciones Biológicas Aplicadas; Argentina Fil: Echeverría, Hernán Eduardo. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires. Estación Experimental Agropecuaria Balcarce; Argentina

No-tillage maize (Zea mays L.) grown without adequate N intercepts less than 95% of the incident radiation at flowering. Reducing the distance between rows could increase radiation interception and grain yield. A 2-yr experiment was conducted at INTA Research Station, Balcarce, Argentina (37°45' S; 58°18' W), to study the effect of row spacing and N availability on intercepted radiation, kernel number, and grain yield of no-till maize. Treatments consisted of a factorial combination of row width (0.35 and 0.70 m) and N (0 and 120 or 140 kg ha -1 each year) at a constant plant density. Low N decreased kernel number and grain yield. Narrow rows significantly increased kernel number per unit area and grain yield. Average increases in response to narrow rows were 14.5 and 20.5% for kernel number and grain yield, respectively. However, relative increases in response to narrow rows were greater at low N. A close association between kernel number and intercepted radiation during the bracketing-Bilking period was observed. With conventional row spacing, relative grain yield responses to narrower rows decreased as crop radiation intercepted at flowering increased. A decrease in row distance when N was limiting partially offset the negative effects of N deficiency on grain yield. Our results indicate that 27 to 46% increases in grain yield were obtained in response to narrow rows in N-deficient maize crops.

El carbono orgánico total (COT) del suelo por su efecto benéfico sobre las propiedades físicas, químicas y biológicas, es considerado como uno de los principales indicadores de calidad de suelo, por lo que es necesario determinarlo con suficiente exactitud. Para algunos suelos de la Región pampeana y extrapampeana se compararon las técnicas de determinación de COT de Walkley & Black, Walkley & Black modificado y calcinación (LOI) con respecto al método de combustión seca de Dumas, tomado como referencia. Se obtuvo una alta correlación entre las técnicas de determinación de COT (r²=0,98-0,99). Se verificó el factor de corrección de 1,32, usado habitualmente en la metodología de Walkley & Black para convertir el carbono fácilmente oxidable (CFO) en COT. Se observó que la pendiente de la relación entre la MO determinada por LOI y el COT determinado por el método de Dumas (1,697) no difirió del valor de 1,724 habitualmente empleado para la conversión de COT a MO. La metodología de Dumas mostró mayor veracidad y precisión respecto de las demás técnicas de determinación de COT.