103-v42n1-anaerobically-mineralized-nitrogen

ANAEROBICALLY MINERALIZED NITROGEN WITHIN MACROAGGREGATES AS INDICATOR OF WHEAT NITROGEN NUTRITION

Vanesa García Gisela1,2,*, Nahuel Ignacio Reussi-Calvo1,2, Nicolás Wyngaard1,2, Fernanda Covacevich2,3, Guillermo Alberto Studdert1

1 Facultad de Ciencias Agrarias, UNMdP, Unidad Integrada Balcarce

2 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)

3 Instituto de Investigaciones en Biodiversidad y Biotecnología-Fundación para las Investigaciones Biológicas Aplicadas.

ABSTRACT

This work aimed to evaluate the capacity of anaerobically mineralized nitrogen (AN) within large (ANLM), small (ANSM), and total macroaggregates (ANTM) to predict grain yield, aboveground biomass, and total nitrogen (N) content of wheat (Triticum aestivum L.) plants as compared to AN in bulk soil (ANBS). Eight fields with non-N-fertilized wheat on Mollisols of the southeastern Argentinean Pampas were studied. Soil ANBS, ANLM, ANSM, and ANTM, and wheat grain yield, aboveground biomass, and plant total N content were determined. The ANLM, ANSM, and ANTM were positively related to grain yield, aboveground biomass, and plant total N content (R2=0.34-0.65). The relationships between ANBS and all those crop variables showed similar predictive capacity. Therefore, AN within macroaggregates was not a better indicator of soil nitrogen supply capacity than ANBS.

Keywords: grain yield; aboveground biomass; total nitrogen.

NITRÓGENO MINERALIZADO EN ANAEROBIOSIS EN MACROAGREGADOS COMO INDICADOR DE LA NUTRICIÓN NITROGENADA DE TRIGO

RESUMEN

El objetivo de este trabajo fue evaluar la capacidad del nitrógeno mineralizado en anaerobiosis (AN) determinado dentro de macroagregados grandes (ANLM), macroagregados chicos (ANSM) y macroagregados totales (ANTM) para predecir el rendimiento en grano, la biomasa aérea y el contenido de nitrógeno total en planta de trigo (Triticum aestivum L.) sin fertilización nitrogenada comparado con el AN determinado en la masa total del suelo (ANBS). Fueron estudiados ocho lotes con trigo sin fertilización nitrogenada en Molisoles del sudeste de la Región Pampeana Argentina. El ANBS, el ANLM, el ANSM, el ANTM, el rendimiento en grano, la biomasa aérea y el contenido de nitrógeno total en planta fueron determinados. El ANLM, el ANSM y el ANTM estuvieron relacionados con el rendimiento en grano, la biomasa aérea y el contenido de nitrógeno total en planta (R2=0.34-0.65). Las relaciones entre el ANBS y todas aquellas variables mostraron capacidades predictivas similares. Por lo tanto, el AN en macroagregados no fue un mejor indicador de la capacidad del suelo de suministrar nitrógeno que el ANBS.

Palabras clave: rendimiento en grano; biomasa aérea; nitrógeno total.

INTRODUCTION

Nitrogen (N) is the most influential nutrient for crop yield and quality (Echeverría & Sainz Rozas, 2014). Nitrogen fertilizer recommendations are generally based on bridging the gap between the grain yield of a non-N-fertilized crop and its grain yield potential with no N limitations under specific edaphoclimatic conditions (Correndo et al., 2021). Thus, the grain yield without N fertilization is determined by the soil N supply capacity (Reussi Calvo et al., 2013). In order to make sustainable decisions regarding N fertilization management, it is necessary to develop and use models for predicting the grain yield of unfertilized crops at its planting time or early growth stages (Archontoulis et al., 2020). However, such prediction is usually complex due to the large number of factors involved in the N dynamics (Archontoulis et al., 2020; Correndo et al., 2021). Along this line, N mineralization indicators are very important to help estimating the soil N availability, since they allow estimating the amount of N mineralized from the soil organic matter throughout the crop cycle (García & Reussi Calvo, 2014).

Potentially mineralizable N is considered the standard method to determine the nitrogen mineralization potential of a soil under laboratory conditions. However, it requires long incubation periods for its determination (>200 days), which restricts its use as a method for N fertility diagnosis for N fertilization recommendations in soil testing labs (Echeverría & Sainz Rozas, 2014). Consequently, numerous soil variables have been suggested as alternatives to potentially mineralizable N (Schomberg et al., 2009). One of such variables is the anaerobically mineralized N (AN) in the bulk soil (ANBS), which involves a short (i.e., 7 days) anaerobic incubation period of soil samples (Keeney, 1982). Considering that ANBS is strongly related to potentially mineralizable N, ANBS has been proposed as a quick, simple, and precise alternative to estimate potentially mineralizable N (Schomberg et al., 2009). In this sense, it has been reported that ANBS is positively associated with grain yields of non-N-fertilized corn (Zea mays L.) (Orcellet et al., 2017), wheat (Triticum aestivum L.) (Reussi Calvo et al., 2013), and barley (Hordeum vulgare L.) (Queirolo, 2018). The incorporation of ANBS determined at 0-20 cm depth to the traditional methods for the N availability diagnosis has improved their capacity to predict grain yield of unfertilized crops and the response to N fertilization of wheat (Reussi Calvo et al., 2013) and corn (Orcellet et al., 2017). Such improvement allows a more precise and reliable determination of N fertilizer rates, leading to a more efficient and environmentally safer use of nitrogen fertilizers.

In Mollisols from temperate regions, macroaggregates (250-8000 µm) have a key role in the functioning of soil (García et al., 2021; Roldán et al., 2014). Since the concentration of organic fractions in soil macroaggregates is more sensitive to management practices than those determined in bulk soil (Roldán et al., 2014), AN within large (2000-8000 µm, ANLM), small (250-2000 µm, ANSM), and/or total macroaggregates (250-8000 µm, ANTM) may be better indicators of soil N availability. Thus, ANLM, ANSM, and ANTM could be more closely related than ANBS to productive traits (grain yield, and aboveground biomass dry matter, and plant N accumulation) than ANBS. The determination of AN within macroaggregates would allow a more precise N-fertilizer recommendation, reducing the economic and environmental impact of fertilization. The objective of this work was to evaluate the capacity of ANLM, ANSM, and ANTM to predict grain yield, aboveground biomass, and plant total N plant content, as compared with ANBS in non-N-fertilized wheat crops on Mollisols of the Southeastern Argentinean Pampas.

MATERIALS AND METHODS

In 2018, eight rainfed wheat fields of farms from the southeastern Argentinean Pampas (Figure 1) were selected to take soil and plant samples. Soils were Mollisols with surface textural classes typical of the region (i.e. loam, clay-loam, sandy-loam, and sandy-clay-loam, Rubio et al., 2019), and no evidence of erosion (slope<2%) or flooding. The climate in this area is classified as mesothermal subhumid-humid (according to the Thornthwaite classification) or as temperate humid without a dry season (according to the Köpen classification). Median annual rainfall ranges from 759 mm (West) to 950 mm (East), and mean air temperature ranges from 14.1 °C (South) to 15.1 °C (North). In each field, a 400 m2 plot was delimited and georeferenced, and those plots were preserved from receiving N fertilization. Wheat was sown between June and July of 2018, using intermediate-growing-season varieties recommended for this region. Weeds, pests, and diseases control was done by the farmers, and the tillage system was no-tillage in all the fields.

Diagrama

Descripción generada automáticamente

Figure 1: Sampling sites (circles) throughout the southeastern Buenos Aires province at the Argentinean Pampas.

Figura 1: Sitios de muestreo (círculos) en el sudeste de la provincia de Buenos Aires en la Región Pampeana argentina.

At wheat sowing (June and July of 2018) composite soil samples (5 subsamples) were taken at 0-20 cm depth using a tubular sampler at field capacity to determine ANBS in the unfertilized plots. The samples were dried at 50 °C until constant weight and ground to pass through a 2000-μm sieve removing all identifiable plant material. These samples were later used to determine ANBS. Additional composite soil samples were taken at 0-20 cm depth with a shovel (5 subsamples from each plot) to determine ANLM, ANSM, and ANTM. Upon extraction, aggregates were carefully and manually separated to pass through an 8000-μm sieve, removing all identifiable plant material, and then dried at 50 °C until constant weight. Macroaggregates separation was performed as described by Six et al. (1998). In detail, 100 g aliquot of dry aggregates were capillary re-wetted for 24 h until field capacity. Re-wetted aggregates were placed on the 2000-µm-mesh sieve and submerged in water for 5 min. After that, large macroaggregates and small macroaggregates were separated by sieving in water for 2-min (50 3-cm-run up and down oscillations) on a 2000 µm and 250 µm sieve, respectively. Aggregate fractions were back-washed from the sieve, allowed to flocculate for 24 h, and oven-dried at 50 °C until constant weight after removing the supernatant. Dry large and small macroaggregates were ground with mortar and pestle to pass through a 500-μm sieve. The ANBS, ANLM, and ANSM were determined through short anaerobic incubation for 7 d at 40 °C (Keeney, 1982), and ammonium-N quantified by steam distillation (Keeney & Nelson, 1982). The ANBS was expressed in mg ammonium-N per kg-1 bulk soil dry mass, whereas ANLM and ANSM were expressed in mg ammonium-N per kg-1 large and small macroaggregates dry mass, respectively. The ANTM was calculated through the average of ANLM and ANSM weighted by the mass proportion of large and small macroaggregates masses, respectively. Additionally, soil samples were taken at 0-60 cm in each plot to determine N as nitrate through extraction with potassium sulfate and quantification by spectrophotometry (Keeney & Nelson, 1982).

At wheat physiological maturity, aboveground biomass samples were randomly taken in each plot from three 9-m-long crop rows. Samples were dried at 60 °C until constant weight and weighed, and aboveground biomass was determined as the sum of the dry matter of leaves and stems, and grain yield. Then, spikes were separated from the rest of the plant (leaf and stem), threshed with a stationary thresher, and grains were weighted. Grain yield was expressed at 14% moisture. Both grains and leaves and stems were ground to pass through a 500-μm sieve to determine plant total N content by wet combustion followed by steam distillation (Bremner & Mulvaney, 1982). All crop variables (i.e., grain yield, aboveground biomass, and total N) were expressed as mass per area unit (i.e., kg ha-1).

Water availability throughout the crop cycle was calculated as the sum of soil available water at sowing and rainfall during the crop growth cycle (i.e., from July to December). Available water in the soil at sowing was 150 mm considering that the soil profile was at field capacity (Carpaneto & Lanzavecchia, 2016). Rainfall records were obtained from records of weather stations located near the experiments (< 5 km). The association between variables was evaluated through Pearson correlation coefficients and simple linear regression and linear-plateau models. Statistical analyses were performed with R software (R Core Team, 2020). A significance level of 0.05 was used.

RESULTS

Minimum, mean, and maximum values of AN within macroaggregates (i.e. ANLM, ANSM, and ANTM), ANBS, N as nitrate, and crop variables are presented in Table 1. Available water during the crop cycle ranged between 400 and 845 mm, with a mean value of 587 mm. Nitrogen as nitrate was not correlated to ANLM, ANSM, ANTM, ANBS, and grain yield, but it was correlated to aboveground biomass (r=0.65) and plant total N (r=0.64). The ANBS was related to grain yield (pseudo-R2=0.67, Figure 2a) and aboveground biomass (pseudo-R2=0.39, Figure 2b) through linear-plateau models. Grain yield increased with aboveground biomass up to an estimated value of 58.2 mg kg-1, beyond which it stabilized at 6058 kg ha-1 (Figure 2a). The relationship between aboveground biomass and ANBS showed a similar behavior showing an ANBS threshold of 57.1 mg kg-1, beyond which aboveground biomass stabilized at 13212.7 kg ha-1 (Figure 2b). The ANBS was linear and positively related to plant total N (R2=0.48, Figure 2c).

Table 1: Minimum, mean, and maximum values of anaerobically mineralized nitrogen (AN) in bulk soil (ANBS), AN in large macroaggregates (2000-8000 µm, ANLM), AN in small macroaggregates (250-2000 µm, ANSM), AN in total macroaggregates (250-8000 µm, ANTM), nitrogen as nitrate (N-NO3-), yield grain, aboveground biomass, and plant total nitrogen content of wheat without nitrogen fertilization.

Tabla 1: Valores mínimos, medios y máximos de nitrógeno mineralizado en anaerobiosis (AN) en la masa total del suelo (ANBS), AN en macroagregados grandes (2000-8000 µm, ANLM), AN en macroagregados chicos (250-2000 µm, ANSM), AN en macroagregados totales (250-8000 µm, ANTM), nitrógeno como nitrato (N-NO3-), rendimiento en grano, biomasa aérea y nitrógeno total en planta de trigo sin fertilización nitrogenada.

Variable	n	Minimum	Mean	Maximum
ANBS (mg kg-1)	8	44.4	61.5	95.0
ANLM (mg kg-1)	8	48.2	72.0	109.4
ANSM (mg kg-1)	8	53.9	72.3	111.7
ANTM (mg kg-1)	8	49.4	72.1	109.9
N-NO3- (mg kg-1)	8	4.6	9.7	23.1
Grain yield (kg ha-1)	24	2893.4	5217.6	7818.7
Aboveground biomass (kg ha-1)	24	7257.1	12084.7	16000.0
Total nitrogen (kg ha-1)	24	66.0	110.2	166.7

Figure 2: Relationships between anaerobically mineralized nitrogen (AN) in bulk soil (ANBS) and yield grain (GY) (a), aboveground biomass (AB) (b), and total nitrogen in plant (TN) (c) of wheat without nitrogen fertilization (n = 24).

Figura 2: Relaciones entre el nitrógeno mineralizado en anaerobiosis (AN) en la masa total del suelo (ANBS) y el rendimiento en grano (GY) (a), la biomasa aérea (AB) (b), y el nitrógeno total en planta (TN) (c) de trigo sin fertilización nitrogenada (n = 24).

The ANLM, ANSM, and ANTM were positive and closely correlated to ANBS (r of 0.87, 0.81, and 0.87, respectively). The AN within macroaggregates (i.e., ANLM, ANSM, and/or ANTM) were related to grain yield (Figure 3a, d, g, respectively), aboveground biomass (Figure 3b, e, h, respectively), and plant total N (Figure 3c, f, i, respectively) through different models, depending on the analyzed variables. The ANLM, ANSM, and ANTM were related to grain yield (Figure 3a, d, g, respectively) and aboveground biomass (Figure 3b, e, h, respectively) through linear-plateau models. Grain yield and aboveground biomass increased with the increase of AN within macroaggregates up to estimated values between 64.7 and 69.0 mg kg-1, respectively, beyond which grain yield and aboveground biomass stabilized at average values of 5713 and 13330 kg ha-1, respectively. The AN within macroaggregates was related to plant total N (Figure 3c, f, i) through linear models. Model fittings of the relationships between ANLM, ANSM, and ANTM and grain yield (Figure 3a, d, g, respectively, pseudo-R2 of 0.52, 0.38, and 0.50, respectively) and plant total N (Figure 3c, f, i, respectively, R2 of 0.46, 0.34, and 0.44, respectively) were lower than those between ANBS and grain yield (Figure 2a, pseudo-R2 of 0.67) and plant total N (Figure 2c, R2 of 0.48), respectively. Contrarily, higher pseudo-R2 were found between AN within macroaggregates (i.e., ANLM, ANSM, and ANTM) and aboveground biomass (Figure 3b, e, h, pseudo-R2 of 0.62, 0.65, and 0.64, respectively) than between ANBS and aboveground biomass (Figure 2b, R2 of 0.39)

Figure 3: Relations between anaerobically mineralized nitrogen (AN) in large macroaggregates (2000-8000 µm) (ANLM) and yield grain (GY) (a), aboveground biomass (AB) (b), and total nitrogen in plant (TN) (c), AN in small macroaggregates (250-2000 µm) (ANSM) and GY (d), AB (e), and TN (f), AN in total macroaggregates (250-2000 µm) (ANTM) and GY (g), AB (h), and TN (i) of wheat without nitrogen fertilization (n = 24).

Figura 3: Relaciones entre el nitrógeno mineralizado en anaerobiosis (AN) en macroagregados grandes (2000-8000 µm) (ANLM) y el rendimiento en grano (GY) (a), la biomasa aérea (AB) (b), y el nitrógeno total en planta (TN) (c), el AN en macroagregados chicos (250-2000 µm) (ANSM) y el GY (d), la AB (e), y el TN (f), el AN en macroagregados totales (250-2000 µm) (ANTM) y el GY (g), la AB (h), y el TN (i) de trigo sin fertilización nitrogenada (n = 24).

DISCUSSION

The mean value of grain yield without N fertilization recorded at this study was greater (Table 1) than the average wheat grain yield at the studied area during the same year (4614 kg ha-1) and at the previous 15 years (4240 kg ha-1) (MAGyP, 2020). No water limitations were observed during the crop growing season since water availability exceeded crop water demand (i.e. 385 mm, Abbate, 2017) in all experiments.

Given that AN within macroaggregates was related to crop variables (Figure 3), our results suggest that ANLM, ANSM, and ANTM are indicators of wheat performance and, specifically, of the soil N availability during the growing season, as ANBS is. In general, the relationships between AN within macroaggregates and crop variables (Figure 3) presented a similar behavior as the relations between ANBS and crop variables (Figure 2). This could be due to the close relations between ANBS and AN within macroaggregates (i.e., ANLM, ANSM, and/or ANTM). Similar relations between ANBS and AN within macroaggregates were reported by other authors in Mollisols (García et al., 2021; Gregorutti et al., 2014; Rivero et al., 2020) and Vertisols (Gregorutti et al., 2014). These results indicate that the largest proportion of organic nitrogen that is quantified through ANBS is found in macroaggregates (García et al., 2021; Gregorutti et al., 2014; Rivero et al., 2020).

The ANBS and AN within macroaggregates (i.e., ANLM, ANSM, and/or ANTM) explained reasonably well the grain yield variability (pseudo-R2 between 0.38 and 0.67, Figure 2a, 3a, e, i) and the aboveground biomass variability (pseudo-R2 between 0.39 and 0.65, Figure 2b, 3b, f, j). For the southeastern Argentinean Pampas soils, other authors reported positive linear relations between ANBS and grain yield in unfertilized barley (Queirolo, 2018) and wheat (Reussi Calvo et al., 2013) crops, in which ANBS explained 45% and 41% of grain yield variability, respectively.

The associations between ANBS, ANLM, ANSM, and ANTM with total nitrogen (Figure 2c) confirm that AN expresses the soil nitrogen supply capacity (Reussi Calvo et al., 2013). The ANBS and AN within macroaggregates (i.e., ANLM, ANSM, and/or ANTM) explained as much variability of plant total N (34-48%, Figure 2c, 3c, g, k) as reported by Reussi Calvo et al. (2013) for wheat.

Although no differences were observed between AN within macroaggregates (i.e., ANLM, ANSM, and/or ANTM) and ANBS in their ability to predict wheat grain yield (lower pseudo-R2, Figure 3a, d, g vs Figure 2a) and plant total N content (Figure 3c, f, i vs Figure 2c), AN within macroaggregates was a better indicator of aboveground biomass (Figure 3b, e, h vs Figure 2b). Previous studies have reported that ANLM and ANTM were not better indicators of soil properties (i.e. total and particulate organic carbon, and aggregate stability) than ANBS (García et al., 2021; Rivero et al., 2020).

CONCLUSION

Under the conditions of this study, ANLM, ANSM, and ANTM were not better indicators of grain yield and plant total N than ANBS. For this reason and considering that grain yield was better explained by ANBS than by AN within large, small and/or total macroaggregates, the determination of ANBS would be enough to estimate the capacity of soils to supply N. This allows to predict wheat N nutrition, allowing precise N-fertilizer recommendations. Hence, it would not be necessary to use a more complex procedure to determine AN within macroaggregates, which additionally demands more careful sampling and conditioning of soil samples to avoid aggregate disturbance, and the separation of macroaggregates through water sieving after capillary wetting.

ACKNOWLEDGMENTS

Part of the results presented in this work corresponds to the Doctoral Dissertation of the senior author at the Programa de Posgrado en Ciencias Agrarias, Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata, Argentina. This work was supported by the Universidad Nacional de Mar del Plata (AGR653/21 and AGR689/22), the Fondo para la Investigación Científica y Tecnológica (PICT-2021-I-INVI-00619), and the Instituto Nacional de Tecnología Agropecuaria (PNCyO 1127032), Argentina. The authors want to express their deep appreciation to the farmers who allowed soil sampling in their fields and data collection and use for this study.

REFERENCES

Abbate, P. E. (2017). Bases ecofisiológicas del manejo del cultivo de trigo en la Región Pampeana. En G. A. Divito y F. O. García (Eds.), Manual del Cultivo de Trigo (pp. 33-52. International Plant Nutrition Institute.

Archontoulis, S. V., Castellano, M. J., Licht, M. A., Nichols, V., Baum, M., Huber, I., Martinez-Feria, R., Puntel, L., Ordóñez, R.A., Iqbal, J., Wright, E.E., Dietzel, R.N., Helmers, M., Vanloocke, A., Liebman, M., Hatfield, J. L., Herzmann, D., Córdova, S. C., Edmonds, P., Togliatti, K., Kessler, A., Danalatos, G., Pasley, H., Pederson, C. & Lamkey, K.R. (2020). Predicting crop yields and soil-plant nitrogen dynamics in the US Corn Belt. Crop Science, 60,721-738. https://doi.org/ 10.1002/csc2.20039

Bremner, J. M. & Mulvaney, Y. C. (1982). Nitrogen total. In A. L. Page (Ed.), Methods of soil analysis. Part 2. Chemical and microbiological properties. (2a ed., Agronomy Monograph 9) (pp. 595-624). Am. Soc. Agron. Inc. – Soil Sci. Soc. Am. Inc.

Carpaneto, B. y Lanzavecchia, L. (2016). Informe agropecuario mensual. Red de Información Agropecuaria Mensual Estación Experimental Agropecuaria del Instituto Nacional de Tecnología Agropecuaria Balcarce, 122, 1-12.

Correndo, A. A., Rotundo, J. L., Tremblay, N., Archontoulis, S., Coulter, J. A., Ruiz-Diaz, D., Franzen, D., Franzluebbers, A. J., Nafziger, E., Schwalbert, R., Steinke, K., Williams, J., Messina, C.D. & Ciampitti, I. A. (2021). Assessing the uncertainty of maize yield without nitrogen fertilization. Field Crops Research, 260,107985. https://doi.org/10.1016/j.fcr.2020.107985

Echeverría, H. E. & Sainz Rozas, H. R. (2014). Nitrógeno. En H. E. Echeverría y F. O. García (Ed.), Fertilidad de suelos y fertilización de cultivos (2a ed.) (pp. 189-228). Ediciones INTA.

García, F. O. & Reussi Calvo, N. I. (2014). Trigo. En H. E. Echeverría y F. O. García (Eds.), Fertilidad de suelos y fertilización de cultivos (2a ed.) (pp. 401-434). Ediciones INTA.

García, G. V., Campos, M. E., Wyngaard, N., Reussi Calvo, N. I., San Martino, S., Covacevich, F. & Studdert, G. A. (2021). Anaerobically mineralized nitrogen within macroaggregates as a soil health indicator. Catena, 198,105034. https://doi.org/10.1016/j.catena.2020.105034

Gregorutti, V. C., Novelli, L. E., Melchiori, R. J. M., Ormaechea, M. V. y Caviglia, O. P. (2014). Nitrógeno incubado en anaerobiosis y su relación con el nitrógeno orgánico en diferentes fracciones. Ciencia del Suelo, 32(1),1-11.

Keeney, D. R. (1982). Nitrogen-availability indexes. En A. L. Page (Ed.), Methods of soil analysis. Part 2. Chemical and microbiological properties. (2a ed., Agronomy Monograph 9) (pp. 711-733). Am. Soc. Agron. Inc. – Soil Sci. Soc. Am. Inc.

Keeney, D. R. & Nelson, D. W. (1982). Nitrogen inorganic forms. En A. L. Page (Ed.), Methods of soil analysis. Part 2. Chemical and microbiological properties. (2a ed., Agronomy Monograph 9) (pp. 643-698). Am. Soc. Agron. Inc. – Soil Sci. Soc. Am. Inc.

Ministerio de Agricultura, Ganadería y Pesca (MAGyP). (2020). Agricultura-estimaciones agrícolas. Datos agricultura, ganadería y pesca [dataset]. Sitio web https://datos.magyp.gob.ar/dataset/estimaciones-agricolas.

Orcellet, J. M., Reussi Calvo, N. I., Sainz Rozas, H. R., Wyngaard, N. & Echeverría, H. E. (2017). Anaerobically incubated nitrogen improved nitrogen diagnosis in corn. Agronomy Journal, 109(1),291-298. https://doi.org/10.2134/agronj2016.02.0115

Queirolo, I. (2018). Manejo del nitrógeno para incrementar la eficiencia de uso y la calidad en cebada cervecera [Tesis de Maestría no publicada]. Universidad Nacional de Mar del Plata.

R Core Team. (2020). R: A language and environment for statistical computing. Sitio web https://www.R- project.org/.

Reussi Calvo, N. I., Sainz Rozas, H., Echeverría, H. E. & Berardo, A. (2013). Contribution of anaerobically incubated nitrogen to the diagnosis of nitrogen status in spring wheat. Agronomy Journal, 105(2),1-8. https://doi.org/10.2134/agronj2012.0287

Rivero, C., Tourn, S. N., García, G. V., Videla, C. C., Domínguez, G. F. & Studdert, G. A. (2020). Nitrogen mineralized in anaerobiosis as indicator of soil aggregate stability. Agronomy Journal, 112(1),592-607. https://doi.org/ 10.1002/agj2.20056

Roldán, M. F., Studdert, G., Videla, C. C., San Martino, S. y Picone, L. I. (2014). Distribución de tamaño y estabilidad de agregados en molisoles bajo labranzas contrastantes. Ciencia del Suelo, 32(2),247-257.

Rubio, G., Pereyra, F. X. & Taboada, M. A. (2019). Soils of the Pampean Region. In G. Rubio, R. S. Lavado & F. X. Pereyra (Eds.) The Soils of Argentina (pp. 81-100). Springer Int. Publ.

Schomberg, H. H., Wietholter, S., Griffin, T. S., Reeves, D. W., Cabrera, M. L. & Fisher, D. S. (2009). Assessing indices for predicting potential nitrogen mineralization in soils under different management systems. Soil Science Society of America Journal, 73(5),1575-1586. https://doi.org/10.2136/sssaj2008.0303

Six, J., Elliott, E. T., Paustian, K. & Doran, J.W. (1998). Aggregation and soil organic matter accumulation in cultivated and native grassland soils. Soil Science Society of America Journal, 62(5),1367-1377.