Resumen. En el sudoeste de la provincia de Buenos Aires (Argentina) las deficiencias de nitrógeno (N) y fósforo (P) son factores limitantes del rendimiento de trigo. El objetivo de este trabajo fue informar sobre la efectividad comparativa de fosfato diamónico (DAP) y superfosfato triple (TSP) en una variedad de suelos y años. Entre 1983 y 1992, 13 experimentos se llevaron a cabo en lotes de productores del área. El diseño de los experimentos fue de bloques divididos completos aleatorizados. Los tratamientos horizontales fueron dosis (0 a 135 kg producto/ha) y fuentes de fósforo (DAP y TSP). Los suelos pertenecen a los subórdenes Ustoles y Udoles. Los tratamientos verticales fueron testigo y una dosis única de urea aplicada a la siembra o macollaje. La respuesta del trigo a los tratamientos horizontales fue significativa en cuatro experimentos llevados a cabo en los Ustoles. DAP y TSP se compararon mediante el cálculo del índice de la relación de eficiencias (ER) y el valor de sustitución (SV), que se define como la relación entre las dosis de TSP/DAP a las que se obtiene la misma respuesta en rendimiento. ER del DAP con respecto a TSP estuvo entre 0,82 y 1,28. En dos de los cuatro experimentos, el valor SV estuvo por encima del cociente entre los respectivos precios de DAP y TSP, que se estima en alrededor de 1.1. Esto significa que, en esos casos, DAP no sólo fue más eficaz que TSP sino también una fuente más rentable. SV parece ser un parámetro más útil que ER porque cubre un rango mayor de dosis. Independientemente de la significación, los rendimientos con DAP fueron alrededor de 60 kg/ ha superiores que para TSP, en un promedio de todos los experimentos y las dosis de fertilizantes.

In the southwest of Buenos Aires Province (Argentina), nitrogen (N) and phosphorus (P) deficiencies are important wheat yield limiting factors. There is an information gap regarding differences between single element and binary N-P sources. The objective of this paper was to develop a general model for N-P fertilization in the area that also quantified diammonium phosphate (DAP) effect and its interactions with N-urea, applied at sowing or tillering, as compared with triple superphosphate (TSP). Between 1984 and 1985, 13 experiments were carried out in farmer's fields N. With the yield data for each experiment, a yield function was fitted which included terms for single effects of urea (0, 30 and 60 kg N/ha) and 80 kg/ha of either DAP or TSP. Yield response variables were derived from the equation. Measured site variables were pH, organic matter (OM) and soil extractable phosphorus (Bray-P). Categorical variables of soil texture, wheat cycle and previous soil use were also included. Regressions were developed between dependent and site variables. The set of equations constituted a model that explained 31 to 75% of the variation in the yield response variables. Agronomic efficiency of N-urea for soils with agricultural use was around 12 kg wheat/kg N for both times of application. Response to DAP and TSP was related to Bray-P and soil texture. The bridging experiments between these two P sources estimated a superiority of DAP of around 180 and 90 kg wheat/80 kg of fertilizer on coarse and medium textured soils, respectively. Although it is physically impossible to isolate N-P effects in a binary fertilizer, this may be attributed to additional N. The data also suggested synergism between DAP and urea applied at sowing after their interaction in the soil.

n the characterization of the initial state of a long-term experiment (ELD) under no-till, we hypothesized that there are horizontal and vertical fertility gradients in the topsoil. The objective of this paper is to describe and to quantify those variations in a block design wheat fertilization experiment in the field of the National University of the South (UNS), Argentina. In a slightly inclined field 4 blocks were located across the slope. Soil depth was 80 cm at the top and increased downward to 100 cm. The soil was classified as a Petrocalcic Paleustoll, thermic coarse loam. Composite samples of each block were taken at the depths of 0-6, 0-12, and 0-20 cm. They were air-dried and sieved through 2 000 µm. Determinations were: pH; electrical conductivity (CE); cation exchange capacity (CIC); exchangeable cations: calcium (Ca int ), magnesium (Mg int ), potassium (K int ) and sodium (Na int ); extractable nutrients: phosphorus (P BK ), sulphur (S-SO 4 2- ), boron (B ext ), iron (Fe ext ), manganese (Mn ext ), copper (Cu ext ) and zinc (Zn ext ). In samples sieved through 500 µm total organic carbon (COT) and nitrogen (N ot ) were determined. Walkley & Black (W-B) was used for analysis of easily oxidizable organic carbon (COX 24 ), lower H 2 SO 4 concentrations of 12 and 18 N were used for further determinations (COX 12 and COX 18 ). Results were analyzed using descriptive statistics, t test for paired means and regressions. Soil organic carbon variables and oxidation factor for W-B were consistent with low intensity use of native grasses in the plot selected as a starting point for the ELD. The range of pH values (7.3-8.0) reflected base saturation, with ideal levels of Ca int , Mg int and K int . Nutrient availability was high for S-SO 4 2- , B ext , Fe ext and Mn ext , moderate for Cu ext and Zn ext and low for P BK . The coefficient of variation (CV) was between 7 and 11 % for ten variables. The most stable were pH, Mg int , CIC, C:N and Cu ext (CV < 7 %). Others (COX 12 , N ot , Mn ext and Zn ext ) showed greater variability (CV 11-20 %) and P BK (CV 33.9 %). The statistical treatment of the space variability was adapted to the block design and sampling depths. In 12 out of 20 parameters, sampling depth and/or the position of the blocks explained over 30 % of the observed variations. The changes in depth of P BK , K int and cation micronutrients (with the exception of the Cu ext ) can be associated to their scarce mobility in the soil. The position in the slope with potential effects on available water and biomass production, would explain the gradients in CIC, Ca int and organic carbon. The opposite trend found for P BK is attributed to its negative non-significant relation with pH. This variability study approach can enhance monitoring of soil chemical properties in the ELD.

Corn has not only a high growth potential and a great capacity of biological response to suitable crop management but also may contribute to a better match of crops with environmental offer in Argentina. Nitrogen (N) fertilization must make provision for eventual N losses, and fertilization strategies must be designed so as to minimize their global incidence. The different quick-release N sources show similar efficiencies when they are incorporated, but in surface applications, sources that contain little or no amidic N have a better performance than urea (U). The objective of this paper was to make an evaluation of corn response to N applied in V6 without incorporation, using two different solid N sources. A field experiment was carried out during 2004, in a farm located 30 km away from General Pico (La Pampa, Argentina), to evaluate corn response to N rates (0 - 120 kg/ha) sidedressed in V6 without incorporation, using U or a commercial mixture of ammonium nitrate and dolomite (ND). Rainfall and temperatures were ideal during the crop cycle. The excellent growing conditions reflected in high corn yields. The results showed that N fertilization affected virtually all yield components. Yield was on average 2417 kg of grain/ha greater in the ND than in the U treatments. For a N rate below 85 kg/ha, agronomic efficiency was of 65 and 87 kg of corn per kg of applied N for U and ND, respectively. Apparent fertilizer N recovery was 1.14 and 1.34 kg absorbed N per kg applied N for U and ND, respectively. For the kind of soil, cultivar and growing conditions of the experiment, a substitution value of 1.6 can be used to estimate ND-N rates from models developed for U-N.

Corn has not only a high growth potential and a great capacity of biological response to suitable crop management but also may contribute to a better match of crops with environmental of- fer in Argentina. Nitrogen (N) fertilization must make provision for eventual N losses, and fertilization strategies must be designed so as to minimize their global incidence. The different quick-release N sources show similar efficiencies when they are incorporated, but in surface applications, sources that contain little or no amidic N have a better performance than urea (U). The objective of this paper was to make an evaluation of corn response to N applied in V6 without incorporation, using two different solid N sources. A field experi - ment was carried out during 2004, in a farm located 30 km away from General Pico (La Pampa, Argentina), to evaluate corn response to N rates (0 - 120 kg/ha) sidedressed in V6 without incorporation, using U or a commercial mixture of ammonium nitrate and dolomite (ND). Rainfall and temperatures were ideal during the crop cycle. The excellent growing conditions reflected in high corn yields. The results showed that N fertilization affected virtually all yield compo - nents. Yield was on average 2417 kg of grain/ha greater in the ND than in the U treatments. For a N rate below 85 kg/ha, agronomic efficiency was of 65 and 87 kg of corn per kg of applied N for U and ND, respectively. Apparent fertilizer N recovery was 1.14 and 1.34 kg absorbed N per kg applied N for U and ND, respectively. For the kind of soil, cultivar and growing conditions of the experiment, a substitution value of 1.6 can be used to estimate ND-N rates from models developed for U-N.

In the characterization of the initial state of a long-term experiment (ELD) under no-till, we hypothesized that there are horizontal and vertical fertility gradients in the topsoil. The objective of this paper is to describe and to quantify those variations in a block design wheat fertilization experiment in the field of the National University of the South (UNS), Argentina. In a slightly inclined field 4 blocks were located across the slope. Soil depth was 80 cm at the top and increased downward to 100 cm. The soil was classified as a Petrocalcic Paleustoll, thermic coarse loam. Composite samples of each block were taken at the depths of 0-6, 0-12, and 0-20 cm. They were air-dried and sieved through 2 000 mu m. Determinations were: pH; electrical conductivity (CE); cation exchange capacity (CIC); exchangeable cations: calcium (Ca-int), magnesium (Mg-int), potassium (K-int) and sodium (Na-int); extractable nutrients: phosphorus (PBK), sulphur (S-SO4 (2-)), boron (B-ext), iron (Fe-ext), manganese (Mn-ext), copper (Cu-ext) and zinc (Zn-ext). In samples sieved through 500 mu m total organic carbon (COT) and nitrogen (Not) were determined. Walkley & Black (W-B) was used for analysis of easily oxidizable organic carbon (COX24), lower H2SO4 concentrations of 12 and 18 N were used for further determinations (COX12 and COX18). Results were analyzed using descriptive statistics, t test for paired means and regressions. Soil organic carbon variables and oxidation factor for W-B were consistent with low intensity use of native grasses in the plot selected as a starting point for the ELD. The range of pH values (7.3-8.0) reflected base saturation, with ideal levels of Caint, Mgint and Kint. Nutrient availability was high for S-SO4 (2-), Bext, Feext and Mnext, moderate for Cuext and Znext and low for PBK. The coefficient of variation (CV) was between 7 and 11 % for ten variables. The most stable were pH, Mgint, CIC, C: N and Cuext (CV < 7%). Others (COX12, Not, Mnext and Znext) showed greater variability (CV 11-20 %) and PBK (CV 33.9 %). The statistical treatment of the space variability was adapted to the block design and sampling depths. In 12 out of 20 parameters, sampling depth and/or the position of the blocks explained over 30% of the observed variations. The changes in depth of PBK, Kint and cation micronutrients (with the exception of the Cu-ext) can be associated to their scarce mobility in the soil. The position in the slope with potential effects on available water and biomass production, would explain the gradients in CIC, Caint and organic carbon. The opposite trend found for PBK is attributed to its negative non-significant relation with pH. This variability study approach can enhance monitoring of soil chemical properties in the ELD.

The objective of this paper was to report on the relative effectiveness of urea (U – 46% N) and calcium ammonium nitrate (CAN – 27% N) for wheat fertilization in southwestern Buenos Aires Province (Argentina). Five experiments were carried out between 1996 and 1998. Treatments were N rates (0 to 45/60 kg ha-1) and sources (U and CAN), applied broadcast at tillering. Crop variables studied were: crop yield (CY), protein grain concentration (CPG) and N yield (NY). Effect of sources was analyzed by comparison of crop variables for individual treatments and by the calculation of two parameters i) efficiency ratio (ER) and ii) substitution value (SV). CAN treatments gave higher values of CY and NY in 4 of the 5 experiments and of CPG in 50% of the cases. However, none of these were significant. Both ER and SV varied with experiments. ER was around 1.35, 1.25 and 0.98 for CY, NY and CPG. This means on average CY response was 35% higher for plots fertilized with CAN, with very little reduction of CPG. SV was around 1.5 for CY, i.e. U attained the same CY as CAN if U rates were increased by 50%. An advantage of using SV for CY is that direct comparisons with price ratios can be made for a simple economic analysis. CAN superiority was related not only to a greater N apparent recovery but also to increased physiological efficiency. This could be explained through the different availability in time of the two sources

-1 . N-P interaction was greater for soils of low organic matter and cultivars of intermediate and short vegetative cycle. Interaction between the two N fractions of a split application was related to pH and the higher yield response potential of the intermediate cycle cultivar. The results indicate that it is more convenient to split the N rate, particularly for long and intermediate cycle cultivars.

In the southwest of Buenos Aires Province (Argentina) nitrogen and phosphorus deficiencies are important wheat yield limiting factors. The objective of this paper was to develop a model which predicted yield response to nitrogen (0 to 60 kg N ha-1), applied at two different times (sowing or tillering) or in a split application, and to include the interaction with phosphorus (16 kg P ha-1), applied with the seed. For each of 19 experiments, placed on farmers’ fields, a function of the form y = b0 + b1Ns + b2 Nm + b3 Ns 2 + b4 Nm 2 + b5 NsxNm + b6 P + b7 NsxP + b8 NmxP + b9 NsxNmxP, was fitted. In the equation y denotes yield; N and P, fertilizer rates; subscripts s and m, time of application and b0 to b9, coefficients. Dependent variables of yield response to N and P and interactions were derived from this equation. Independent variables were pH, organic matter (MO) and soil extractable phosphorus (BK). Dummy variables of soil texture, wheat cycle and climatic year were also included. Yield response to N and P depended mainly on climatic year and BK, respectively, as shown in previous papers. Interactions accounted for ± 500 kg wheat ha-1. N-P interaction was greater for soils of low organic matter and cultivars of intermediate and short vegetative cycle. Interaction between the two N fractions of a split application was related to pH and the higher yield response potential of the intermediate cycle cultivar. The results indicate that it is more convenient to split the N rate, particularly for long and intermediate cycle cultivars.

In the Southwest of Buenos Aires Province (Argentina), wheat yields are limited by phosphorus (P) deficiencies in at least 50% of the area. The objective of this paper was to report on the relative efficiency of two different methods of application of P fertilizer: (i) by row placement with the seed at sowing (RP) and (ii) by broadcasting and incorporation into the surface soil (BP). The design of the experiments was of complete blocks with a strip subplot. Treatments were P rates and method of application. Subtreatments were N fertilization at different times and rates. P fertilizer was triple superphosphate (TSP). One experiment included diammonium phosphate (DAP). Yield response to P was significant in 3 of the 4 experiments. The RP produced higher yields in three experiments, but differences were significant in only one site. The RP effects on yield are shown by comparison of yields for individual treatment rates and by the calculation of fertilizer efficiency, efficiency ratio and substitution rate (S), which is defined as the ratio of RP and BP rates rendering the same yield response. Of these, the substitution rate showed the most highly significant effects. Fertilizer efficiency for TSP broadcast ranged from 8 to 44 kg wheat kg(-1) P. Efficiency ratio of RP to BP for a rate of 16 kg P ha(-1) was between 1.27 and 1.74. The S was significant in two experiments carried out on sandy loams where values of 0.31 and 0.39 were found for soils with 6 and 10 mg P kg(-1) (Bray I). In general, RP improved wheat quality as determined by kernel and volume weight and also the ability of the crop to compete with weeds (Avena fatua).

The objective of this research was to develop a general soil fertility model for nitrogen (N) in the south west of Buenos Aires Province (Argentina) which i) explained the regional variations in soil fertility and response of wheat (Triticum aestivum L.) to N fertilizer, and ii) predicted the most profitable N rates. Between 1980 and 1986, 28 fertilization experiments in wheat were established on N-deficient farmers' fields in the area. Dependent variables were Y (mean yield), Al (overall efficiency of fertilizer), and B2 (curvature adjustment). Independent variables included site, crop, and climate factors. For the two times of fertilization (sowing and tillering), Y was found to be strongly related to organic matter content (OM) for a given climatic year and Al was mainly determined by September rainfall (S). B2 depended on OM and was affected by the time of fertilization for the selection of other variables. A recommendation chart for farmers was derived for a relevant price ratio of 8.