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Recent reviews about soybean nitrogen (N) requirement have speculated about a possible N limitation in high-yield environments (>4.5 Mg ha−1). However, these studies did not provide definitive experimental data to test that hypothesis and results from the literature are conflicting. To fill this knowledge gap, we evaluated N limitation across 13 high-yield soybean environments in Argentina and USA. Each experiment included a ‘zero-N’ treatment, which forced the crop to rely on biological N2 fixation and indigenous soil N, and a ‘full-N’ treatment, which provided an ample fertilizer N supply during the entire crop cycle based on site-specific yield potential. Accumulated N in aboveground dry matter (ADM) measured in a N-omission maize plot grown adjacent to the soybean experiments was used to determine indigenous soil N supply. Soybean seed yield, protein and oil concentration, ADM, harvest index (HI), accumulated N in ADM, N harvest index (NHI), and seed N were measured in both treatments at physiological maturity. A simple conceptual framework relating ADM with accumulated N was used to assess treatment differences in ADM, accumulated N, and N-use efficiency (NUE). To account for treatment differences in seed biomass composition, mass-based ADM was expressed in glucose equivalents (ADMe). Seed yield ranged from 4.6 to 6.7 Mg ha−1 (full-N) and 4 to 5.8 Mg ha−1 (zero-N), with the full-N treatment averaging 12% (0.6 Mg ha−1) and 3% (9 g kg−1) higher seed yield and protein concentration, respectively. The full-N treatment exhibited 18% (70 kg N ha−1) and 14% (1.6 Mg ha−1) greater accumulated N and ADM, respectively, compared with the zero N treatment, without changes in HI and NHI, but slightly lower NUE (29 versus 30 kg ADM kg−1 N in full and zero-N, respectively). However, NUE differences between treatments became indistinguishable when ADM was expressed as ADMe (45 kg glucose kg−1 N). The (full-N minus zero-N) seed yield difference and the indigenous soil N supply were negatively associated. This research documented (i) the existence of N limitation in high-yield soybean, (ii) that seed yield and protein concentration increases were physiologically associated with changes in accumulated N (but not in NUE and/or NHI), and (iii) that the degree of N limitation is modulated by indigenous soil N supply. Findings from this study can serve as a basis to identify environments with the largest N limitation and thus guide N management in soybean.

Precision agriculture has under delivered partially because it has been based on technologies focused on increasing the resolution of spatial variation in soil and yield and more recently automation, with less effort in incorporating the physiological principles of crop responses to environmental variation. Here we show how a whole-farm precision agriculture approach accounting for the physiological processes underlying the relationship between environment and crop development, growth and yield (“zone management”), bridge yield gaps, increased farmer profit and reduced risk, on San Lorenzo, a 5000 ha dryland farm in the southern Pampas. The farm grows wheat and barley in winter, and soybean, maize, and sunflower in summer; winter grain cereal/double-cropped soybean is a main activity. Four management zones were defined: i) Zone 1, shallow soils (< 0.8 m) with low frost risk and deep water table (> 3 m below surface); ii) Zone 2, intermediate soil depth (0.8 to 1.8 m) with low frost risk and deep water table; iii) Zone 3, deep soils (> 1.8 m) with low frost risk and deep water table; and iv) Zone 4, deep soils (> 1.8 m) with high frost risk and water table < 3 m from surface. Crop choice and practices were tailored to each zone based on ecophysiological principles including the relative sensitivity of crop growth and yield to soil depth, frost and water supply during the species-specific critical window for yield determination; for example, maize is the most sensitive crop to stress during its critical window, therefore it was excluded from Zone 1 and 2, with a substantial reduction of risk and improvement of farm output (amount of grains that can be produced in a hectare) and profit. In comparison with neighboring farms, San Lorenzo had a 54% higher farm output, and 46% higher gross margin (or 112 US$ ha−1 year−1); this was driven by a higher net income (244 US$ ha−1) despite increased total costs (132 US$ ha−1). Fil: Monzon, Juan Pablo. Universidad Nacional de Mar del Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina Fil: Calviño, P. A.. Asociación Argentina de Consorcios Regionales de Experimentación Agrícola; Argentina Fil: Sadras, Victor Oscar. Universidad Nacional de Mar del Plata; Argentina. South Australian Research And Development Institute; Australia Fil: Zubiaurre, J. B.. San Lorenzo Farmer; Argentina Fil: Andrade, Fernando Héctor. Unidad Integrada Balcarce; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata; Argentina

As soybean yield continues to increase, it seems critical to know if there is a yield level at which potential contribution of indigenous nitrogen (N) sources (N fixation and soil mineralization) becomes insufficient to meet crop N requirements for high yields, while still maintaining or increasing protein and oil concentration. We have hypothesized that, in absence of other limiting factors, degree of N limitation increases with increasing yield potential (Yp) of the production environment. To test this hypothesis, we developed a novel protocol to ensure an ample N supply during the entire crop season (full-N treatment). That protocol was applied to field-grown irrigated soybean in Balcarce (Argentina) and Nebraska (USA), where measured full-N seed yields were ±15% of their simulated Yp in 92% of the cases. The combination of locations, years, sowing dates, and N treatments resulted in a wide range of seed yields, from 2.5 to 6.5 Mg ha−1. Overall, full-N seed yield averaged 11% higher than seed yield without N addition (zero-N). However, magnitude of yield difference between full-N and zero-N depended upon Yp, ranging from no detectable yield difference in low-Yp (ca. 2.5 Mg ha−1) to up to 900 kg ha−1 in high-Yp environments (ca. 6 Mg ha−1). Seed yield differences were associated with higher aboveground dry matter, seed number, and seed weight in the full-N versus zero-N treatments. Seed protein (but not oil) concentration was higher in the full-N treatment, and both protein and oil yields were higher in the full-N versus zero-N treatments. Findings from this study indicate that (i) N limits soybean seed yield (as well as protein yield, and oil yield) in environments with high Yp, where indigenous N sources seem insufficient to fully satisfy crop N requirements, and (ii) yield response to N fertilizer can occur above a 2.5 Mg ha−1 Yp threshold and has an upper limit of 250 kg seed per Mg increase in Yp. Fil: Cafaro la Menza, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Nebraska; Estados Unidos Fil: Monzon, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina Fil: Specht, James E.. University of Nebraska; Estados Unidos Fil: Grassini, Patricio. University of Nebraska; Estados Unidos

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

Seed number (SN) is positively associated with aboveground dry matter (ADM) accumulation in most crop species. In soybean, there are discrepancies among studies relative to the start and end of the critical period for seed number determination. The objective of this study was to more precisely identify those two stages. To do so, we followed two approaches: (i) analyses of experimental data where differences in SN occurred as a result of variation in crop growth due to weather and management practices and (ii) review of published experiments where soybean was subjected to artificial stresses during specific crop phases. Following the first approach, we analyzed the relationships between SN versus ADM accumulation and its components, crop growth rate (CGR) and duration, for different reproductive phases using data from experiments that portrayed a wide range of environments and management practices. In the second approach, we compared SN values in stressed versus non-stressed treatments. Accumulated ADM during the R3 to R6 phase explained ca. 70 % of the variation in SN across experiments. The CGR during R3-R6 was also a good predictor of SN, but it had lower explanatory power compared with accumulated ADM, because CGR did not account for changes in duration of critical period across experiments. Review of published data, wherein soybean crops were subjected to artificial stresses during different reproductive phases, confirmed that the R3-R6 phase is a critical phase for SN determination in soybean. Key findings of this study were: (i) critical period for SN determination in soybean occurs during the R3-R6 phase and (ii) accumulated ADM during the critical period is a better predictor of SN compared with CGR because it accounts for differences in the duration of the critical period as a result of weather and management.

Favorable weather conditions prevailing on most South American Pampas allows to grow more than one crop per year. Indeed, increasing crop intensity per unit area has been highlighted as an opportunity to increase crop production in a high food demanding world scenario. Previous studies have analyzed cropping-system yield gap by aggregating crop yields either as total amount of grain or as unit of energy. However, few cropping-system yield gap analysis have made a distinction between single (i.e., soybean sown as a single crop per year) and double-cropped soybean (i.e., soybean sown immediately after harvest of a winter cereal crop), and none of them at a country level. This article focuses on the estimation of cropping system-imposed yield gap (CSIYg), which is defined as the difference of seed yield between single soybean and double-cropped soybean. The aims of the present study were: (i) to analyze yield potential (Yp), water-limited (Yw) and yield gap (Yg) spatial and interannual variability; (ii) to investigate the concept of CSIYg for soybean using cropping systems in Uruguay as a proof of concept; and (iii) to assess differences on yield variability between single and double-cropped soybean. Yp and Yw were estimated for single and double-cropped soybean in specific locations within the major soybean crop producing areas using CROPGROW model coupled with long-term good quality weather data, soil types and dominant management practices. Estimations were scaled up following the protocols of the Global Yield Gap Atlas project. We applied a boundary function analysis to assess the differences on Yw variability between single and double-cropped soybean. At country level Yp was estimated on 6.6 and 5.7 Mg ha−1 for single and double-cropped soybean, respectively. However, we found lower differences on Yw between single and double-cropped soybean (3.6 and 3.4 Mg ha−1, respectively). We estimated CSIYg due to combined effect of weather condition and water regime on 3.2 Mg ha−1. The CSIYg representing the combined effect of weather condition, water regime and management was estimated on 1.6 Mg ha−1. Double-cropped and single soybean showed the same Yw response to precipitations and a similar Yw variability (t-test P = 0.55). Our results highlight double-cropped soybean cropping systems as an alternative for increasing grain production in this main agricultural region of the world.

After canopy closure and in the absence of limitations by water or nutrient availability, crop growth rate (CGR) of maize (Zea mays L.) is ultimately constrained by the daily incident radiation and temperature of the environment. Sustaining maximal canopy photosynthetic capacity after-flowering is, then, a necessary but not a sufficient condition to increase maize dry-matter production. The aim of the present study was to determine the extent of the photo-thermal environment limitation to CGR during the post-flowering period in current maize crops. Dynamic of CGR was studied in two well-irrigated and nourished maize field experiments (Exp. 1 and Exp. 2 for 2010−11 and 2011−12 cropping seasons, respectively) on conventional crops (i.e. full-season hybrid planted early in the season) at Balcarce, Argentina (37° 45’ S, 58° 18’ W; 130 m a.s.l.). Two independent methods were performed to benchmark the CGR of these conventional crops during the post-flowering period: i) empirical CGR values obtained under the same weather conditions from younger maize crops, and ii) theoretically estimated potential CGR, obtained as a function of daily incident radiation and potential radiation use-efficiency (RUE). Conventional crops reached the maximal CGR near flowering in mid-January, being 51.2 g m−2 d−1 and 58.8 g m−2 d−1 in Exp. 1 and Exp. 2, respectively. Afterwards, CGR decreased progressively towards crops maturity late in March. Estimates, from either the empirical or the theoretical method, indicated that although attainable-CGR decreases progressively towards the end of the cropping season, it sustains higher values than those achieved by conventional crops after flowering. Differences in attainable vs. actual-CGR was almost exclusively attributable to RUE, which, in turn, could not be explained solely by the post-flowering foliar nitrogen withdrawal. Differences between actual (1987 g m−2 in Exp. 1 and 1614 g m−2 in Exp. 2) and potential post-flowering dry-matter production defined gaps that were in the range 18.2%–47.8%. From these results, it can be concluded that the photo-thermal environment is not, at least so far, the limiting factor to the post-flowering maize growth. Further research is needed, however, to analyze the viability of increasing potential yield of maize through the closure of these estimated gaps.

Favorable climate and soils for rainfed crop production, together with a relatively low population density, results in 70–90% of Argentina grain production being exported. No assessment to date has tried to estimate the potential for extra grain production for soybean, wheat and maize, which account for 78% of total harvested area, by yield gap closure on existing cropland area and its impact at a global scale. The objectives of this paper are (i) to estimate how much additional grain could be produced without expanding crop area by closing yield gaps in Argentina, (ii) to investigate how this production and yield gaps varies across regions and years, and (iii) to analyze how these inter-annual variations are related to El Niño—Southern Oscillation phenomenon (ENSO). Production increase on existing crop area was assessed for soybean, wheat and maize by quantifying the yield gap (Yg), that is, the difference between water-limited yield potential (Yw) and actual yield (Ya). A bottom-up approach was followed to estimate Yw and Yg, in which these parameters were first estimated for specific locations in major crop producing areas and subsequently up-scaled to country level based on spatial distribution of crop area and climate zones. Locally-calibrated crop simulation models were used to estimate Yw at each selected location based on long-term weather data and dominant soil types and management practices. For the analyzed period, the national level Yg represented 41% of Yw for both wheat and maize and 32% of the Yw for soybean. If farmers had closed Yg from these levels to 20% of Yw, Argentina could have increased soybean, wheat and maize production by a respective 7.4, 5.2, and 9.2 Mt, without expanding cropland area. This additional production would have represented an increase of 9%, 4%, and 9% of soybean, wheat, and maize global exports. This potential grain surplus was, however, highly variable because of the ENSO phenomenon: attainable soybean production was 12 Mt higher in favorable “El Niño” years compared with unfavorable “La Niña” years. Interestingly, Yg tended to be higher in wet years, suggesting that farmers do not take full advantage of years with favorable conditions for rainfed crop production. Regional variation in Yg was found in Argentina highlighting the usefulness of this work as a framework to target research and, ultimately, reduce gaps in areas where current yields are well below their potential. EEA Balcarce Fil: Aramburu Merlos, Fernando. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Unidad Integrada. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Monzon, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Mercau, Jorge Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria San Luis; Argentina Fil: Taboada, Miguel Angel. Instituto Nacional de Tecnología Agropecuaria (INTA). Instituto de Suelos; Argentina Fil: Andrade, Fernando Hector. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce. Unidad Integrada. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Hall, Antonio Juan. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Jobbagy Gampel, Esteban Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi"; Argentina Fil: Cassman, Kenneth G. Universidad de Nebraska - Lincoln. Department of Agronomy and Horticulture; Estados Unidos Fil: Grassini, Patricio. Universidad de Nebraska - Lincoln. Department of Agronomy and Horticulture; Estados Unidos

Delaying maize (Zea mays L.) sowing date can diminish grain yields through reductions in the number, size and activity of growing grains (sink strength) and/or reductions in the assimilate supply (source capacity) to grains during the grain filling period. Whether the source capacity or the sink strength is the limiting factor for grain yield in late sown maize still remains unclear. Understanding source-sink relationships is relevant to optimize crop management practices, to identify critical processes for crop modelling and to develop breeding strategies. The objective of this work was to assess the effect of delays in maize sowing date on grain yield components and on the source-sink relationship during the grain filling period. Three well irrigated and fertilized maize field experiments were conducted at Balcarce, Argentina (37° 45′ S, 58° 18′ W; 130 m a.s.l.) during 2009–10; 2010–11 and 2011–12 cropping seasons. Sowing dates ranged from October to January covering a broad range of the seasonal photo-thermal variation. Grain yield was affected by sowing date and varied from 1680 g m−2 (early sowings) to 203 g m−2 (late sowings). Grain number per unit area was reduced proportionally less than weight per grain as sowing date was delayed. Variations in grain yield were related to the harvest index, and were closely associated with dry matter accumulation during the post-silking period. The variation of source capacity was higher than that of sink strength during the grain filling period and the source/sink ratio decreased from early to late sowing dates. Results indicate that crop growth during the grain filling period was limited by the sink strength in early sowing dates and by the photosynthetic source capacity in the late ones. Fil: Bonelli, Lucas Emmanuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Monzon, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Cerrudo, Anibal Alejandro. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Rizzalli, Roberto H.. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Andrade, Fernando Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina

Favourable prices and new technologies have recently stimulated the adoption of wheat–soybean double crops in the south-eastern Pampas. To assess the largely unknown long-term performance of this strategy, we used CERES-Wheat and CROPGRO-Soybean with slight adaptations to account for double cropping. Models and climate records were combined to analyse management practices allowing for earlier soybean sowing, which was assumed to be the key for high soybean yield and whole-system performance. Practices investigated were: (i) short-season wheat cultivars; (ii) non-selective herbicides for faster drying of wheat before harvest; (iii) relay double cropping, where soybean is sown on standing wheat before crop maturity in contrast to sequential cropping where soybean is sown after wheat harvest. Models reproduced phenology and yield of crops in double cropping systems to the level required for our investigation. Advancing wheat harvest with herbicides and using current early wheat varieties had little impact on soybean yield. A hypothetical frost-resistant wheat allowing for earlier wheat sowing and harvest highlighted the potential to increase the yield of sequential soybean by 23%. Average soybean yield increased from 1738 kg ha −1 in sequential to 2099 kg ha −1 in relay cropping, whereas wheat yield was similar in both cropping variants. Seasonal variability in rainfall and simulated yield was partially accounted by the Southern Oscillation Index (SOI), indicating the potential for this signal to be used in risk management. The amount of rainfall during the period of yield generation in wheat and the remaining soil water at the end of the wheat growing season were higher during consistently negative SOI phase, and lower during consistently positive phase in September. In the period between 1971 and 2003 average October–December temperature increased at 0.038 °C year −1 . Higher temperature accelerated simulated wheat development and advanced harvest (0.15 day year −1 ) with no impact on yield; this allowed for earlier sowing of double cropped soybean, which together with more favourable temperature increased simulated soybean yield at a rate of 26.2 kg ha −1 year −1 . Hence, our modelling study indicated that: (i) wheat–soybean relay double cropping outperformed its sequential counterpart, (ii) seasonal variability in rainfall and yield could be partially accounted by Southern Oscillation Index (SOI) and (iii) long-term trends in crop phenology and yield could be associated with increased mean temperature.

Phenological development is the most important attribute of crop adaptation and long-term changes in phenology provide strong evidence of the biological impact of warmer climates. This paper takes the documented increase in temperature during the last decades as a starting point, and quantifies the changes in wheat phenology in (a) 53 locations in eastern Australia between 1957 and 2000 using the APSIM model, and (b) 17 locations in the Pampas between 1971 and 2000, using CERES-Wheat. The expectation is shortened season length associated with warmer climate; the aim is to quantify the actual magnitude of phenological changes, the relative changes in the duration of pre- and post-flowering phases, and the interaction between changing temperature and sowing date. Modelled time from sowing to maturity was reduced up to ∼0.3 d y−1; time to flowering accounted for most of the variation in time to maturity. The rate of change in the duration of modelled wheat phenophases was more marked with early sowing. Owing to the cumulative effect of temperature on crop development assumed in the models, significant changes in rate of development were detected in some cases when change in temperature was statistically undetected. A minimum rate of mean temperature increase ∼0.02 °C y−1 was required for significant shortening of time to flowering and season length. In agreement with rates derived from field experiments, the rate of change in modelled time to flowering and maturity was ≈7 d °C−1. The duration of the post-flowering phase was largely unchanged. This was associated with lack of change in temperature, or where temperature increased, earlier flowering that shifted post-flowering development to relatively cooler conditions, thus neutralising the trend of increasing temperature.

The effect of stubble mulch on soil water storage during fallow is highly variable. In environments with low rainfall and coarse-textured soil, contribution of stubble to gains in water storage is often smaller than in wetter environments with heavier soil. While this pattern is recognised, the effect of rainfall, evaporative demand and soil remains confounded. This paper investigates the effect of stubble on soil evaporation and soil water storage during fallow in contrasting environments at Balcarce (Argentina) and Walpeup (Australia). Field and modelling experiments were combined to quantify stubble effects on soil evaporation and water storage for loam (Balcarce) and sandy loam soils (Walpeup). Simulations with the CropSyst model and long-term weather records included reference evapotranspiration from 185 to 240 mm, and rainfall from 108 to 471 mm for the winter fallow period at Balcarce, and reference evapotranspiration from 595 to 686 mm, and rainfall from 46 to 305 mm for the summer fallow period at Walpeup. The effect of size of rainfall events, quantified with power laws, was emphasised. Amount of rainfall during fallow accounted for most of the variation in soil evaporation, irrespective of reference evapotranspiration and soil type. For bare soil, evaporation was lower than expected in years with higher frequency of large rainfall events, but no relationship between soil evaporation and size of rainfall event was found for soil with stubble. The response of soil evaporation and soil water storage to rainfall comprised three phases. In the first phase, all the rainfall was evaporated irrespective of soil cover; hence, there were no benefits of stubble in terms of water storage. In the second phase, stubble reduced soil evaporation with respect to bare soil, with a subsequent gain in soil water. In the third phase, the benefit of stubble declines up to the point in which rainfall is high enough to meet evaporative and storage demands irrespectively of soil cover. It is proposed that gains in stored soil water due to stubble could be estimated as a function of rainfall using a non-linear model with locally adjusted parameters.

Cultivating multiple crops as a land use alternative could increase system productivity and sustainability, providing options to soybean monoculture for the Argentinean Pampas. This study evaluates the performance of maize-soybean in double crop, relay crop and intercrop across a wide range of water supply and length of growing season in the Pampas. It also assesses the effect of maize cycle length and maize and soybean prices on these intensification alternatives. A total of 16 experiments, 6 rainfed and 10 irrigated, were conducted at four INTA Research Stations during five growing seasons. Yield ranged from 4390 to 16,862kgha-1, for sole maize crops, and from 1884 to 5130kgha-1, for sole soybean crops. The intensification alternatives productivity, measured as the land equivalent ratio (LER), was associated to the length of the growing season and was higher than 1.00 in 100%, 86% and 61% of the cases for maize-soybean double crop, relay crop and intercrop, respectively. Maize grain yield in double crop was similar to that of sole maize crop, whereas soybean yield in double crop was reduced compared to that of sole soybean crop due to sowing date delay. Maize and soybean grain yields under relay crop and intercrop were lower than their respective sole crops. The intercrop increased soybean yield and decreased maize yield compared with relay crop. Yield of soybean in intercrop and relay crop increased when sown with short cycle length maize hybrids. Maize and soybean sole crop yields were positively correlated (P

Maize responses to individual management factors have been widely investigated but studies of higher-order interactions involving multiple factors are rare. This paper investigates the responses of grain yield and water use efficiency of rainfed maize to sowing date, stubble condition, hybrids of contrasting cycle length, soil depth and their interactions, and how these responses are affected by El Niño – Southern Oscillation (ENSO) phenomenon. Grain yield and water balance were modelled with CropSyst using 33 years of weather data for eight locations in an east–west transect in the Southern Pampas of Argentina. Modelled grain yield decreased westward, in parallel with decreasing rainfall. Southern Oscillation Index (SOI) discriminated crop season rainfall and grain yield, with lower rainfall and grain yield for SOI phase Consistently Positive (CP) and higher rainfall and grain yield for SOI phase Consistently Negative (CN). Differences in grain yield between stubble and bare soil were constant across location. High available water, as related to soil depth, increased grain yield across the transect. The effect of sowing date and stubble varied with SOI phase; for CN, highest grain yields were obtained with early sowing whereas for CP grain yield showed no correlation with sowing date. Yield differences between bare soil and stubble conditions were higher under CP than under CN, reflecting the positive effect of stubble in years with rainfall below average. Water use efficiency (WUE = yield per unit evapotranspiration) averaged 19.0 kg ha−1 mm−1 for soils with stubble and 16.5 kg ha−1 mm−1 for bare soil. We conclude that SOI provides an agronomically meaningful predictor of seasonal conditions that can be used to estimate crop production and manage risk by adjusting key management practices. Fil: Monzón, J.P. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Sadras, Victor Oscar. University of Adelaide; Australia Fil: Andrade, Fernando Héctor. Instituto Nacional de Tecnología Agropecuaria; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina

Intercrops are an alternative to intensify and diversify the agricultural systems in the south-east Pampas of Argentina. The aim of this study was to evaluate resource capture and resource use efficiency in maize–soybean and sunflower–soybean intercrops and in their respective sole crops. Water and radiation capture, biomass and grain production were measured for sole crops and intercrops. Water and radiation productivities were estimated as the energy produced per unit of annual available resource. Comparisons of intercrops with soybean sole crops were emphasized because current soybean expansion in the region represents a threat to agricultural system sustainability. Intercrops showed an increase in crop duration when compared to their sole counterparts. Maize–soybean intercrop resulted in an improved radiation and water productivities compared with soybean sole crops. Maize cultivated as sole crop attained the highest resource productivity. On the other hand, resource productivity of sunflower–soybean intercrop was higher than or similar to its corresponding sole crops. The improvement in water productivity for intercrop compared with soybean sole crop was accounted for by an increase in water capture efficiency and, also, by an increase in water use efficiency in the case of maize–soybean intercrop. The increase in radiation productivity for maize–soybean intercrop compared with soybean sole crop was the result of an increase in radiation use efficiency and of a minor but significant increase in radiation capture efficiency. Contrarily, the improvement in radiation productivity of sunflower–soybean intercrop compared with sunflower or soybean sole crops was null or small. Grain yield of intercropped sunflower and maize was 20% lower than yield of sole crops. Therefore, yield attained by intercropping was mainly limited by a poor production of the soybean component. This work provides eco-physiological basis to improve management practices of summer intercrops. Fil: Coll, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Cerrudo, Anibal Alejandro. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina Fil: Rizzalli, Roberto Héctor. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Universidad Nacional de Mar del Plata. Facultad de Ciencias Agrarias; Argentina Fil: Monzon, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina. Consejo Superior de Investigaciones Científicas; España Fil: Andrade, Fernando Héctor. Instituto Nacional de Tecnología Agropecuaria; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina