Crop simulation models are used at the field scale to estimate crop yield potential, optimize current management, and benchmark input-use efficiency. At issue is the ability of crop models to predict local and regional actual yield and total production without need of site-year specific calibration of internal parameters associated with fundamental physiological processes. In this study, a well-validated maize simulation model was used to estimate yield potential for 45 locations across the U.S. Corn Belt, including both irrigated and rainfed environments, during four years (2011-2014) that encompassed diverse weather conditions. Simulations were based on measured weather data, dominant soil properties, and key management practices at each location (including sowing date, hybrid maturity, and plant density). The same set of internal model parameters were used across all site-years. Simulated yields were upscaled from locations to larger spatial domains (county, agricultural district, state, and region), following a bottom-up approach based on a climate zone scheme and distribution of maize harvested area. Simulated yields were compared against actual yields reported at each spatial level, both in absolute terms as well as deviations from long-term averages. Similar comparisons were performed for total maize production, estimated as the product of simulated yields and official statistics on maize harvested area in each year. At county-level, the relationship between simulated and actual yield was better described by a curvilinear model, with decreasing agreement at higher yields (>12 Mg ha-1). Comparison of actual and simulated yield anomalies, as estimated from the yearly yield deviations from the long-term actual and simulated average yield, indicated a linear relationship at county-level. In both cases (absolute yields and yield anomalies comparisons), the agreement increased with increasing spatial aggregation (from county to region). An approach based on long-term actual and simulated yields and year-specific simulated yield allowed estimation of actual yield with a high degree of accuracy at county level (RMSE ≤ 18%), even in years with highly favorable weather or severe drought. Estimates of total production, which are of greatest interest to buyers and sellers in the market, were also in close agreement with actual production (RMSE ≤ 22%). The approach proposed here to estimate yield and production can complement other approaches that rely on surveys, field crop cuttings, and empirical statistical methods and serve as basis for in-season yield and production forecasts.

14Conservation tillage systems (no-tillage, NT; and minimum tillage, MT) are 15 being adopted in rainfed agroecosystems of the Mediterranean basin where 16 water availability is the main limiting factor for crop productivity.We 17 hypothesized that long-term adoption of conservation tillage systems would 18 increase water use efficiency (WUE) and its response to N fertilizer additions 19 due to improved soil water conservation. The long-term sustainability of NT and MT was confirmed. Mean yield and WUE 30 under long-term conservation tillage systems were 66% and 57% higher than 31 under CT, respectively. This improvement was mainly attributed to improved 32 soil water usage under conservation tillage, mainly due to reduced water use 33 during the pre-anthesis period. However, in a wet year yield did not significantly 34 differ among tillage systems. The improvement of WUE with N fertilization was 35 confirmed under NT, which medium and high N fertilizer level increased 98% 36 mean grain yield and 77% mean WUE compared to CT. The increased 37 response of crop and yield to N fertilization under NT was due to improved soil 38 water conservation and more available water for the crop. In this long-term 39 experiment, CT accumulated higher amounts of mineral N on both unfertilized 40 and fertilized plots because the lower yields and hence the lower N uptake 41 compared to NT. Therefore, such soil N accumulation together with the lower 42 water accumulation explained the lack of response to N fertilization under CT, 43 even on a wet growing season (i.e., 2008-2009). 44Long-term NT adoption was a sustainable practice for barley monoculture in the 45 region, allowing for reduced costs and yield increase with N fertilizer additions. 46 N fertilizer rates on rainfed Mediterranean croplands should be adjusted 47 depending on the reduction of tillage intensity and rainfall of the year. In our 48 system and as an example for this agroecosystems, N fertilizer rates should be 49 kept at or below 60 kg N ha

1Management practices can influence soil CO 2 efflux in croplands. Under Mediterranean 2 conditions, soil CO 2 flux responds to tillage and precipitation events with different extent 3 and duration. CO 2 fluxes during these events may constitute a significant part of the annual 4 soil CO 2 emission. Further estimation of these events is required for estimation of the soil C 5 balance and modeling of C dynamics. The long-term effects of tillage practices (NT, no-6 tillage, MT, minimum tillage and CT, conventional tillage) and N fertilization level (zero, 7 medium, 60 kg N ha -1 , and high, 120 kg N ha -1 ) on soil CO 2 fluxes were measured during 8 tillage operations in four consecutive years (2005-2008 period) and during four rainfall 9 events. In all the four years studied, tillage implementation led to a pulse of soil CO 2 flux. 10

The response ofsoil CO2 flux to long-term tillage practices (no-tillage, NT; minimum tillage, MT; conventional tillage, CT) and N fertilization level (zero; medium, 60 kg N ha" ; high, 120 kg N ha~ ) was studied during three growing season in a rainfed Mediterranean agroecosystem. Soil CO^ flux was related to the crop growth, with the highest flux duting spring (i.e., March-May). Tillage and N fertilization effects on soil CO2 flux during growing seasons depended on weather conditions: greater soil COj flux under MT and NT on dry years, greater undet CT and MT on a wet year. Nitrogen fertilization affected soil COj flux during this wet growing season: flux with N fertilizer additions was higher than flux on the unfertilized plots. Thirteen years after establishment ofthe experiment, the soil organic carbon (SOC) stock under long-term NT was 3.9 Mg C ha" greater than under CT and 4.3 Mg C ha"' greater than under MT. The SOC stocks with N fertilizer additions were 4 MgC ha"' greater than the stock on unfertilized plots. The increase of C inputs with N fertilization was more pronounced under NT than under MT or CT. For this reason the incteased response of SOC stock to N fertilization is expected under NT in a longer period of time. The product between soil water content and soil temperature explained between 75 and 94% ofthe seasonal variability ofsoil CO, flux. However, soil COj flux and SOC stock were hardly related.

A field study was conducted at The Experimental Farm, Fac. of Agric., Al-Azahar University, Assuit, located 375 km south of Cairo, Egypt (27° 12-16.67= N latitude and 31° 09-36.86= E longitude) through wheat growing season 2015. The aim of current study is to asses the effect of nitrogen fertilizer types (urea and ureaform) at different levels on soil organic carbon decomposition. Soil organic carbon decomposition percentage (SOCD) is at a minimum amount in the 2 nd week and at a maximum amount in the 7 th week at the recommended urea level-15% (R-15%). The biweekly SOCD % varied from 0.82 and 9.55 % at 70 kg N/fed level (R-30%). SOCD% ranged between 0.16-12.73, 5.14-10.61 and 0.41-8.78% for ureaform level at (R-15%) and (R-30%) less than the recommended one (R), respectively. The amount of soil CO 2 flux from recommended ureaform level treatment was the highest one during the entire growing season. Overall, SOCD% followed the order of R > R-15% > R-30%. The highest values of SOCD % were 8.4 and 8.2 at 2.4 Q 10 value with urea and at 2.7 Q 10 value with ureaform, respectively. The lowest values of SOCD % were 2.3 and 4.4 at 2.2 Q 10 value with urea or ureaform, respectively. Soil C: N raties under all treatments were higher than that of initial state except that under R-30% of urea. The soil C: N ratio was higher at R-15% of urea than that when soil treated by ureaform. The opposite trend is true at R-30%.

Tillage and N fertilization practices contribute to the balance between soil C inputs and outputs. Thus, the impacts of both practices and their interactions on soil organic C (SOC) dynamics must be studied. The main objective of this study was to determine long-term effects of tillage and N fertilization on soil biochemical properties in a longterm experiment established in 1996 on a dryland Typic Xerofluvent soil cropped with barley (Hordeum vulgare L.) in NE Spain. The response of SOC concentration, soil microbial biomass carbon (SMBC) and soil enzyme activities (DHA, dehydrogenase, and PRA, protease) to different tillage (no-tillage, NT; reduced tillage, RT; and conventional tillage, CT) and N treatments (zero, 0 kg N ha-1 ; medium, 60 kg N ha-1 ; and high, 120 kg N ha-1) were measured in 2008 at four soil depths (i.e., 0-5, 5-10, 10-25 and 25-50 cm). All the soil biochemical properties studied showed significant differences for tillage, depth and the interaction between tillage and soil depth. However, N fertilization rates only affected the SMBC content, which was greater under 120 kg N ha-1 than under 0 kg N ha-1 in the 10-25 cm soil layer. In the soil surface layer (0-5 cm), SOC, SMBC and DHA levels in CT were about 50% of the levels in the NT plots. However, in the 10-25 cm soil layer, a greater SOC concentration in CT compared with NT and RT was also accompanied by SMBC and DHA values 30% higher in CT. Below 25 cm soil depth, similar values of soil biochemical properties were found among tillage systems. There was a significant correlation among almost all the parameters studied, with the greatest correlations between SOC and SMBC and between SOC and DHA. In semiarid Mediterranean conditions, after twelve years of experiment, tillage impacted soil biochemical properties in a greater extent compared with N fertilization even though this effect was only limited to the upper soil layers.

Conservation tillage systems are being widely adopted in the Mediterranean region. A long‐term field experiment was established in 1996 comparing three N fertilization levels (zero, 0 kg ha−1; medium, 60 kg ha−1; and high, 120 kg ha−1), under three tillage systems (conventional tillage, CT; minimum tillage, MT; and no‐tillage, NT) in a semiarid Mediterranean agroecosystem annually cropped with winter barley (Hordeum vulgare, L., cultivar Hispanic), to study the response of root growth. During four consecutive growing seasons, from 2005 to 2009, root length density (RLD) and soil water content were evaluated. Penetration resistance (PR) and soil bulk density were only evaluated in the fourth and last year of this experiment. In dry years, root growth was similar under NT and MT systems but highly reduced under CT due to reduced water availability, which, in the surface 25 cm of soil was 7% and 18% lower than under MT and NT systems, respectively. However, in a wet year (i.e., 2009), RLD was double under CT than under NT due to reduced soil strength. PR at 5 to 15 cm soil depth under NT was 1MPa greater than under MT or CT. Root growth was not affected by N fertilization, in contrast to the response of grain yield that showed a significant interaction between N fertilization and tillage system. In spite of moderate soil compaction, which may reduce root growth in wet years, long‐term NT adoption does not reduce grain yields for monoculture of barley under semiarid Mediterranean conditions.

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