ABSTRACT The concentration of linoleic and α-linolenic fatty acids (FA) in grasses can be increased through agronomic techniques; however, there is little information in this regard for tropical grasses. Therefore, the objective of the study was to evaluate the effect of N fertilization and regrowth age management on the FA profile of three tropical grasses. To do this, three plots of 100 m2 each were used for the species: Urochloa decumbens (Stapf) R.D. Webster, U. humidicola (Rendle) Morrone & Zuloaga, and Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs. The study was conducted during dry and rainy seasons. In each period, they were divided into two subplots and only one of them was fertilized. Grass sampling was carried out on days 20, 25, and 30 after fertilization. Five samples were taken from each subplot and an agronomic evaluation was made before each cut. The chemical composition and lipid profile were then determined. An ANOVA of a randomized complete block design with split plot arrangement was performed. The concentration of linoleic and α-linolenic acid was higher in M. maximus during drought (48.5 g 100 g-1 FA) and in U. humidicola during the rainy season (55.1 g 100 g-1 FA). This proportion was higher on day 20 (50.5 g 100 g-1 FA) compared to that recorded on days 25 and 30 (50.1 and 45.7 g 100 g-1 FA, respectively). The fertilized grasses had a higher concentration of linoleic and α-linolenic acid compared to the unfertilized ones (53.4 vs. 44.3 g 100 g-1 FA). It is concluded that fertilization with 50-20-00 (N-P-K) increases the proportion of linoleic and α-linolenic acids in grasses; however, such concentration decreases with increasing plant maturity.

Abstract Chives are one of the most popular spice plants in world cuisine. It is usually produced by small producers, often in an organic farming system. However, research with chives in this production system is lacking. The purpose of this study was to evaluate the production of chives with the use of organic fertilizers before planting and in top dressing. Seven treatments were evaluated, resulting from the factorial 2x3+1, with two organic fertilizers (castor bean cake and hoof and horn powder) x 3 application modes (100% before planting; 100% in top dressing; 50% before planting and 50% in top dressing) + 1 control (without these organic fertilizers). The experimental design was in randomized blocks, with five replications and plots of 1 m2. The relative index of chlorophyll (“Spad” index), height, number of leaves, fresh and dry weight of the plants were evaluated. All treatments of the factorial were better than the control, showing that these organic fertilizers improve production in chives. It is recommended to use the hoof and horn powder in installments (50% before planting and 50% in top dressing) or 100% in top dressing, the latter option being more interesting for reducing the need for labor, with just one application moment.

ABSTRACT Calcium (Ca) is a nutrient responsible for maintaining plant quality and fruit yield. The production of new Ca sources, such as micronized (CaM) and complexed Ca (CaC), and their supplementation provide a better yield in mango cultivation. This study aimed to evaluate the efect of Ca sources (micronized and complexed with Ascophyllum nodosum) and application methods on mango cultivation, in semi-arid Brazil. The experimental design was randomized blocks, in a 6 × 6 factorial scheme. The Ca supplementation strategies (control; 1 L ha−1 of CaM; 2 L ha−1 of CaM; 2 L ha−1 of CaC with A. nodosum extract; 2 L ha−1 of CaC with A. nodosum extract + application of 2.5 L ha−1 via CaC fertigation; and 2.5 L ha−1 via CaC fertigation) were evaluated on six dates regarding nutritional aspects. For biochemical and production aspects, the six supplementation strategies with Ca were evaluated. The Ca concentration in leaves and fruits signifcantly afected the interaction among the factors. The fertilization strategy with 2.5 L ha−1 of complexed calcium via fertigation was fundamental to provide increases in the nitrogen and Ca concentration of the fruits from 65 days after full fowering, and had positive efects on fruiting and production of mangoes cv. Kent.

RESUMO O cálcio (Ca) é um nutriente responsável por manter a qualidade de plantas e o rendimento de frutas. A produção de novas fontes de Ca, como o Ca micronizado (CaM) e o Ca complexado (CaC), e sua suplementação proporcionam um melhor rendimento no cultivo de mangueiras. Avaliou-se o efeito de fontes de Ca (micronizado e complexado com Ascophyllum nodosum) e métodos de aplicação no cultivo de mangueiras, no semiárido brasileiro. O delineamento experimental foi em blocos ao acaso, em esquema fato rial 6 x 6. As estratégias de suplementação de Ca (controle; 1 L ha−1 de CaM; 2 L ha−1 de CaM; 2 L ha−1 de CaC com extrato de A. nodosum; 2 L ha−1 de CaC com extrato de A. nodosum + aplicação de 2,5 L ha−1 via fertirrigação de CaC; e 2,5 L ha−1 via fertirrigação de CaC) foram avaliadas em seis datas, quanto aos aspectos nutricionais. Para aspectos bioquímicos e de produção, as seis estratégias de suplementação com Ca foram avaliadas. A concentração de Ca nas folhas e frutos afetou signifcativamente a interação entre os fatores. A estratégia de fertilização com 2,5 L ha−1 de cálcio complexado via fertirrigação foi fundamental para proporcionar aumentos na concentração de nitrogênio e Ca nos frutos a partir de 65 dias após a foração completa e teve efeitos positivos na frutifcação e produção de mangas cv. Kent.

ABSTRACT Stress caused by defoliation can compromise the physiological quality of soybean seeds. However, there is evidence that the application of nitrogen (N) can be an alternative to reduce the qualitative losses in seeds caused by defoliating insects. The objective of this study was to evaluate the effectiveness of topdressing N fertilization in improving the physiological quality of soybean seeds from plants subjected to artificial defoliation. The experimental design was a randomized block arranged in a 2×4 factorial scheme with four replicates. The treatments consisted of two levels of defoliation (33 and 66%) and four doses of N (0, 50, 100, and 150 kg ha-1), using urea (45% N), applied two days after defoliation. Artificial defoliation was performed during the R3 stage by removing one (33%) and two leaflets (66%) from each trifoliate leaf under field conditions. At stage R5.1, leaf area was quantified, and after harvesting, germination, emergence, length, total dry mass, electrical conductivity, total protein content, mass of 1000 seeds, and tetrazolium (vigor and viability) tests were carried out. It was concluded that increasing the defoliation from 33 to 66% impaired the physiological quality of soybean seeds. The use of nitrogen fertilization for coverage after defoliation at the beginning of the reproductive phase cannot minimize qualitative losses in seeds.

Leachate from a composting plant was characterized and applied as a biofertilizer in lettuce crops. Characteristics of untreated (UE) and anaerobically treated (TE) leachate samples were compared. The pH of TE (8.2) increased in relation to the UE (5.2) due to an increase in ammonia nitrogen in TE (1197 mg L-1) compared to UE (859 mg L-1). Anaerobic treatment was efficient in the removal of organic matter from the leachate, evaluated by the decrease of dissolved organic carbon, biochemical oxygen demand, total organic carbon and total solids. K presented the highest concentration (1743 mg L-1) in TE, followed by Mg (135 mg L-1). Cd, Pb and Cr were present at low concentrations in the samples, 0.047, 0.206 and 0.081 mg L-1, respectively. Salmonella, thermotolerant coliforms and viable helminth eggs were not present in TE, which was applied as a biofertilizer in a lettuce crop and compared to mineral fertilization based on fresh matter and dry matter production. Lettuce production using TE was statistically equivalent to mineral fertilization. Toxic metals were not detected in the lettuce shoots. It was concluded that the anaerobically treated leachate from the composting company has the potential to be used as a biofertilizer.

ABSTRACT In Paraguay, one of the most traditional and massively cultivated crops by producers is the corn, obtaining high yields depends on management practices such as planting time and fertilization management. This research was carried out with the objective of evaluating the effect of fertilization with different nitrogen source, applied 2 times at the late planting season. The following nitrogen fertilizers used were: Urea 30 kg ha-1, Liquid nitrogen (N) 30 kg ha-1, Urea 60 kg ha-1, liquid N 60 kg ha-1, Urea 90 kg ha-1, liquid N 90 kg ha-1 applied in 2 application moments (vegetative state V3 and V6). The experimental design was a factorial arrangement in complete random blocks, considering two factors: 2 sources of N and 3 levels of each source. The weight of 1000 grains, grain yield and agronomic nitrogen efficiency (EAN) were evaluated. The weight of 1000 grains was shown to be influenced both by the application times, as well as by the sources of N and the interaction between both, the yield did not have an effect on the interaction of the factors, while these factors individually had an effect on this variable, the EAN had no effect at the time of application. Liquid N 30 kg ha-1 applied in phenological stage V6 could be recommended as a fertilization practice for corn planted in the late season in southern Paraguay.

RESUMEN En el Paraguay unos de los cultivos más tradicionales y masivamente cultivado por los productores es el maíz, la obtención de altos rendimientos depende de prácticas de manejo como la época de siembra y el manejo de la fertilización, la investigación se realizó con el objetivo de evaluar el efecto de la fertilización con distintas fuentes de nitrógeno aplicados en dos momentos en época tardía de siembra. Se utilizaron como fertilizantes nitrogenados: Urea 30 kg ha-1 Nitrógeno (N) liquido 30 kg ha-1, Urea 60 kg ha-1, N liquido 60 kg ha-1, Urea 90 kg ha-1, N liquido 90 kg ha-1 y dos momentos de aplicación (estado vegetativo V3 y V6). El diseño experimental fue arreglo factorial dispuesto en bloques completos al azar, se consideraron dos factores: dos fuentes de N y tres dosis de cada fuente. Se evaluaron el peso de 1000 granos, rendimiento de granos y la eficiencia agronómica del nitrógeno (EAN). El peso de 1000 granos mostró ser influenciado tanto por los momentos de aplicación, así como por las fuentes de N y la interacción entre ambos, el rendimiento no presentó efecto en la interacción de los factores, mientras que estos factores individualmente presentaron efecto sobre esta variable, la EAN no presentó efecto ante los momentos de aplicación. N liquido 30 kg ha-1 aplicado en estado fenológico V6 se podría recomendar como practica de fertilización del maíz sembrado en época tardía en el sur de Paraguay.

Summary: Swiss chard is a horticultural crop with a highly nutritious value. These crops’ production required nutrients, which can be provided through mineral nutrient solutions or biofertilizers. Biofertilizers are products that contain beneficial microorganisms that improve soil quality and that promote plant growth. Additionally, these microorganisms carry out nitrogen fixation and phosphate solubilization. The present work assessed the application of compost tea, co-inoculation (Azospirillum and Glomus), and inorganic fertilizer over the growth (roots, stem, and leaves) and nutrient content in Swiss chard (Beta vulgaris var. Forhook Giant) plants. The present work was carried out in a greenhouse using a randomized complete block design. Swiss chard plants treated with compost tea + inorganic fertilization (CTIF) accumulated more root and stem dry weight (4.06 and 8.10 g respectively), and, on the other hand, the leaf dry weight increased under three treatments: inorganic fertilization (IF), compost tea + co-inoculation (CTCi) and CTIF (12.5, 9.22 and 10.5 g respectively). Leaf area was greater in the IF and CTIF treatments. In Control (C) P and Mg content were higher; CTCi treatment increased the N, K, and Mn content; the co-inoculation (Ci) treatment increased Cu content as well as CTIF treatment increased the Ca, Fe, Zn, and B contents and in a lesser extent also the P, Mg, Cu, and Mn contents. The biomass partitioning coefficient indicates that in six samples (from a total of seven samples), most of the photosynthates (PS) were used by the plants to form new leaves or to increase the size of the leaves. If an alternative method of fertilization is desired, it is recommended that a combination of biofertilizer and inorganic fertilization should be used, such as, the combination of compost tea and mineral solution that increased the production and the concentration of nutrients in the Swiss chard crop.

Resumen: La acelga es un cultivo hortícola de alto valor nutritivo y en México se producen más de 12 mil toneladas al año. Para su producción, estos cultivos requieren nutrientes, los cuales pueden ser aportados a través de soluciones de nutrientes minerales o biofertilizantes. Los biofertilizantes son productos que contienen microorganismos benéficos que mejoran la calidad del suelo y que favorecen el crecimiento de las plantas. Además, estos microorganismos realizan la fijación de nitrógeno y la solubilización de fosfato. El presente trabajo evaluó la aplicación de té de compost, co-inoculación (Azospirillum y Glomus) y fertilizante inorgánico sobre el crecimiento (raíz, tallo y hojas) y contenido de nutrientes en plantas de acelgas (Beta vulgarisvar. Forhook Giant). El presente trabajo se llevó a cabo en un invernadero utilizando un diseño de bloques completos al azar. Las plantas de acelga tratadas con té de compost + fertilización inorgánica (CTIF) acumularon más peso seco en raíces y tallos (4.06 y 8.10 g respectivamente), por otro lado, el peso seco de la hoja aumentó bajo tres tratamientos: fertilización inorgánica (IF), té de compost + co-inoculación (CTCi) y CTIF (12.5, 9.22 y 10.5 g respectivamente). El área foliar fue mayor en los tratamientos IF y CTIF. El contenido de P y Mg también fue mayor en los controles (C). El tratamiento con CTCi aumentó el contenido de N, K y Mn; el tratamiento de coinoculación (Ci) incrementó el contenido de Cu, así como el tratamiento de CTIF incrementó los contenidos de Ca, Fe, Zn y B y en menor medida también los contenidos de P, Mg, Cu y Mn. El coeficiente de partición de biomasa indica que en seis muestreos (de un total de siete muestreos), la mayoría de los fotosintatos (PS) fueron utilizados por las plantas para formar o aumentar el tamaño de las hojas. Si se desea un método alternativo de fertilización, se recomienda utilizar una combinación de biofertilizante y fertilización inorgánica como la combinación de té de composta y solución mineral que aumentó la producción y la concentración de nutrientes en el cultivo de acelgas.

Summary: In the state of Guerrero, maize (Zea mays) is planted in different soil and climatic conditions, at altitudes ranging from sea level to 2880 altitude meters, mainly in a rainfed regime and by producers who use native and improved maize. The objective is to evaluate the effect of fertilization with nitrogen and phosphorus in combination with silicon on the yield of corn crop components under the hypothesis that at least one fertilization formula and silicon application to the soil generate an positive effect on the size of the corn ear and grain yield. Fertilization consideres two factors; first the Nitrogen, Phosphorus and Potassium (N-P-K) formula with two levels (90-60-00 and 60-40-00); the second was silicon (Si) with three levels (without Si, Fermiphos and Silifosca®), whose combination originated six treatments; which were distributed in a randomized block experimental design with three repetitions. N-P-K fertilization did not statistically affect the variables evaluated, except for diameter, which was statistically different and increased by 2% with 90-60-00. The application of silicon (Fermiphos and Silifosca®) increased cob more than 12% in length and 6% in diameter and grain yield 24%. Fertilization with 90-60-00 + silicon (Fermiphos and Silifosca®) increased size and yield from 8 to 32%; while fertilization with 60-40-00 + silicon (Fermiphos and Silifosca®) exceeded the evaluated parameters from 4 to 28%. Increasing the fertilization formula had minimal and inconsistent impacts on ear size. However, the application of Silifosca® or Fermiphos combined with N-P-K fertilization favored positive changes in ear size and grain yield with 90-60-00 and the addition of Silifosca®.

Resumen: En el estado de Guerrero, el maíz (Zea mays) se siembra en diferentes condiciones edáficas y climáticas, en altitudes que van desde el nivel del mar hasta los 2880 m de altitud, principalmente en régimen de temporal y por productores que utilizan maíces nativos y mejorados. El objetivo fue evaluar el efecto de la fertilización con nitrógeno y fósforo en combinación con silicio en los componentes de rendimiento del cultivo de maíz; bajo la hipótesis de que al menos una fórmula de fertilización y la aplicación de silicio al suelo generan un efecto positivo en el tamaño de la mazorca y el rendimiento de grano de maíz. La fertilización consideró dos factores; primero la fórmula de Nitrógeno, Fosforo y Potasio (N-P-K) con dos niveles (90-60 00 y 60-40-00); el segundo fue la fertilización de silicio (Si) con tres niveles (sin Si, Fermiphos y Silifosca®), cuya combinación originó seis tratamientos; los cuales se distribuyeron en un diseño experimental de bloques al azar con tres repeticiones. La fertilización N-P-K no afectó estadísticamente las variables evaluadas; excepto el diámetro que, fue estadísticamente diferente y se incrementó en 2% con 90-60-00. La aplicación de silicio (Fermiphos y Silifosca®) aumentó más de 12% la longitud y 6% el diámetro de la mazorca y 24% el rendimiento de grano. La fertilización con 90-60-00 + silicio (Fermiphos y Silifosca®) incrementó de 8 a 32% el tamaño y rendimiento; mientras que, la fertilización con 60-40-00 + silicio (Fermiphos y Silifosca®) superó de 4 a 28% los parámetros evaluados. El incremento de la fórmula de fertilización tuvo impactos mínimos y no constantes en el tamaño de la mazorca. Pero, la aplicación de Silifosca® o Fermiphos combinada con la fertilización N-P-K favoreció cambios positivos en el tamaño de la mazorca y rendimiento de grano con 90-60-00 y la adición de Silifosca®.

Resumen Introducción. Tithonia diversifolia (Hemsl.) A. Gray es una planta con alto potencial para alimentación de rumiantes, pero con escasos estudios sobre la comparación el efecto del tipo de fertilización a distintas edades de rebrote sobre el rendimiento y composición nutricional. Objetivo. Evaluar el efecto del tipo de fertilizante y la edad de rebrote sobre rendimiento y composición nutricional del forraje de Tithonia diversifolia. Materiales y métodos. El trabajo se realizó durante el 2020 en la Finca Experimental Santa Lucía de la Universidad Nacional de Costa Rica. Se utilizó un diseño de parcelas divididas completamente al azar con el tipo de fertilizante como parcela principal y la edad de rebrote como subparcela, con tres repeticiones por tratamiento. Los tipos de fertilizante fueron lombricompost, urea y control sin fertilizante, el nitrógeno se aplicó a 150 kg/ha/año. Las edades de rebrote evaluadas fueron 30, 50 y 70 días para un total de nueve tratamientos. Se evaluó la producción de biomasa, relación hoja/tallo y composición nutricional. Se realizó un ANOVA de parcelas divididas para el análisis de datos. Resultados. El tratamiento con urea a 70 días de rebrote presentó la mayor producción de biomasa (77,18 t/ha de materia verde y 7,10 t/ha de materia seca (MS)), la mayor relación hoja/tallo (1,77) se obtuvo en el control a 30 días de rebrote. El tipo de fertilizante mostró efectos significativos sobre la MS, proteína cruda (PC), fibra detergente neutro y carbohidratos no fibrosos (CNF), mientras que la edad de rebrote por sí sola no mostró efectos significativos sobre la fibra detergente neutro digestible y CNF. El mayor contenido de PC se encontró en el tratamiento con urea a 30 días de rebrote (27,61 % PC). Conclusión. La fertilización y la edad de rebrote influyeron sobre el rendimiento y la composición bromatológica de la T. diversifolia. Estos hallazgos contribuyen a la comprensión de la optimización de la producción de T. diversifolia para la alimentación de rumiantes.

Abstract Introduction. Tithonia diversifolia (Hemsl.) A. Gray is a plant with high potential for ruminant feeding, but there is limited research comparing the effects of chemical or organic fertilization at different regrowth ages on its yield and nutritional composition. Objective. To evaluate the effect of the type of fertilizer and the age of regrowth on the yield and nutritional composition of Tithonia diversifolia forage. Materials and methods. The work was conducted in 2020 at the Finca Experimental Santa Lucía of the Universidad Nacional de Costa Rica. A completely randomized divided plot design was employed, with fertilizer type as the main plot and regrowth age as the subplot, with three replicates per treatment. The fertilizer types tested were vermicompost, urea, and a control without fertilizer, with a nitrogen application rate of 150 kg/ha/year. The regrowth ages evaluated were 30, 50, and 70 days for a total of nine treatments. The variables evaluated were biomass production, leaf/stem relation, and nutritional composition. A split plot ANOVA was performed to analyze the data. Results. Among the treatments, the urea treatment with 70 days of regrowth exhibited the highest biomass production (77.18 t/ha of green matter and 7.10 t/ha of dry matter (MS)), while the control treatment with 30 days of regrowth yielded the highest leaf/stem relation (1.77). The type of fertilizer had a significant effect on the variables of MS, crude protein (PC), neutral detergent fiber, and non-fibrous carbohydrates (CNF), whereas regrowth age alone did not significantly affect digestible neutral detergent fiber and CNF. The highest PC content was observed in the urea treatment with 30 days of regrowth (27.61 % PC). Conclusion. Fertilization and regrowth age influenced the yield and bromatological composition of T. diversifolia. These findings contribute to our understanding of optimizing T. diversifolia production for ruminant feeding.

Resumen Introducción. Los forrajes en el trópico presentan una baja digestibilidad, por lo que se buscan alternativas alimenticias como la Tithonia diversifolia (Hemsl.) para aumentar la calidad de la dieta ofrecida. Objetivo. Evaluar el efecto del tipo de fertilizante y la edad de rebrote del forraje de Tithonia diversifolia sobre los parámetros ruminales. Materiales y métodos. El trabajo se realizó en el año 2020 en la Finca Experimental Santa Lucía de la Universidad Nacional, Costa Rica. Se utilizó un diseño de parcelas divididas completamente al azar con el tipo de fertilizante como parcela principal y edad de rebrote como subparcela, con tres repeticiones por tratamiento. Los tipos de fertilizante fueron: lombricompost (L), químico (Q) y control (C) sin fertilizante. Las edades de rebrote evaluadas fueron 30, 50 y 70 días para un total de nueve tratamientos. Las variables evaluadas fueron: cinética de degradabilidad in situ de la materia seca (DISMS), pH, nitrógeno amoniacal (NH3), producción de gas y metano in vitro (CH4). Se realizó un ANDEVA para parcelas divididas. Resultados. La mayor DISMS se encontró en C30 (92,84 %) y menor en Q70 (64,21 %). El tipo de fertilización influyó sobre los contenidos de NH3, el mayor valor se presentó en los tratamientos con fertilización química (275,88 mg NH3/L fluido ruminal). C70 produjo la mayor cantidad de gas (79,59 mL/g), en contraste con Q30 que fue el de menor promedio (28,38 mL/g). La producción de CH4 no mostró diferencias significativas, con valores entre 3,42 y 8,67 mL CH4/g MS. Conclusión. La fertilización y edad de rebrote modificaron los parámetros ruminales in situ e in vitro. Los resultados obtenidos permiten considerar este recurso forrajero como un complemento de las gramíneas de pastoreo en el trópico, donde se generen efectos positivos sobre la digestibilidad de la MS, la producción de gas y de CH4.

Abstract Introduction. Forages in the tropics have low digestibility, which is why alternative feed option such as Tithonia diversifolia (Hemsl.) are sought to improve the quality of the offered diet. Objective. To evaluate the effect of fertilizer type and the regrowth age of Tithonia diversifolia forage on rumimal parameters. Materials and methods. The study was conducted in 2020 at the Santa Lucía Experimental Farm of the Universidad Nacional, Costa Rica. A completely randomized split-plot design was used with fertilizer type as the main plot and regrowth age as subplot, with three replications per treatment. The fertilizer types were: vermicompost (L), chemical (Q), and control (C) without fertilizer use. The evaluated regrowth ages were 30, 50, and 70 days, resulting in a total of nine treatments. The variables assessed were: in situ dry matter degradability kinetics (DISMS), pH, ammoniacal nitrogen (NH3), in vitro gas, and methane production (CH4). An ANOVA was carried out for divided plots. Results. The highest DISMS was found in C30 (92.84 %) and the lowest in Q70 (64.21 %). The type of fertilization influenced NH3 contents, with the highest value observed in chemical fertilizer treatments (275.88 mg NH3/L rumen fluid). C70 produced the highest amount of gas (79.59 mL/g), whereas Q30 had the lowest average (28.38 mL/g). Methane production did not show significant differences, with values ranging from 3.42 to 8.67 mL CH4/g DM. Conclusion. Fertilization and regrowth age modified in situ and in vitro ruminal parameters. The obtained results suggest that this forage resource can be considered a supplement to grazing grasses in the tropics, where positive effects are generated on DM digestibility, gas, and CH4 production.

Abstract Corn is the main crop of the basic basket in Mexico and one of the products of greatest commercial and economic importance nationwide. Among the main factors of agronomic management that determine its level of productivity is fertilization. Currently, as a result of the armed conflicts between Russia and Ukraine, there is a shortage and, consequently, a rise in the price of fertilizers. Therefore, this work studied the fertilization factor in the Papaloapan basin to analyze the effect of chemical nutrition on the corn crop based on its productivity in t ha-1 of grain. Three fertilization scenarios were simulated with the use of the SWAT model, and the results of the factors were mapped by statistically analyzing the difference in means of the treatments through an Anova, which yielded a value of P= 2e-16, showing a significant difference in the effects of the factors analyzed on the yield of the crop. In conclusion, the fertilization factor was higher than the non-fertilization factor, with a difference between means of 7.8 t ha-1 of grain, which indicates that the absence of fertilization work of the crop negatively impacts the productivity of corn grain. Nonetheless, the efficiency between half and full doses of nitrogen fertilization in terms of yield was found to be similar, with the half-dose factor being more efficient than the previous one.

Resumen El maíz es el principal cultivo de la canasta básica en México, así como uno de los productos de mayor importancia comercial y económica a nivel nacional. Dentro de los principales factores del manejo agronómico que determinan su nivel de productividad se encuentra la fertilización. Actualmente derivado de los conflictos bélicos entre Rusia y Ucrania, existe un desabasto y por ende una elevación del precio de los fertilizantes. Por lo anterior, en este trabajo se analizó el factor de fertilización en la cuenca del Papaloapan para analizar el efecto que ejerce la nutrición química en el cultivo de maíz en función de su productividad en t ha-1 de grano. Se simularon tres escenarios de fertilización con el uso del modelo SWAT y se mapearon los resultados de los factores analizando estadísticamente la diferencia de medias de los tratamientos por medio de una Anova la cual arrojó un valor de P= 2e-16 mostrando diferencia significativa en los efectos de los factores analizados sobre el rendimiento del cultivo. En conclusión, el factor de fertilización fue superior al de no fertilización con una diferencia entre medias de 7.8 t ha-1 de grano, lo cual indica que la ausencia de la labor de fertilización del cultivo impacta negativamente sobre la productividad de grano de maíz. Sin embargo, se encontró que la eficiencia entre media dosis y dosis completa de fertilización nitrogenada en términos de rendimiento es similar, siendo el factor de media dosis más eficiente que el anterior.

ABSTRACT Salinity is one of the abiotic stresses that affect gas exchange and growth of pomegranate. In this context, the application of nitrogen fertilizer through the leaves can minimize these effects. Thus, the objective of present study was to evaluate the effect of foliar nitrogen fertilization on pomegranate seedlings irrigated with brackish water. The design used was randomized blocks, in an incomplete factorial scheme (Central Composite Design) with five electrical conductivities of irrigation water - ECw (0.50, 1.15, 2.75, 4.35, and 5.00 dS m-1) and five doses of foliar nitrogen fertilization - FNF (0, 0.33, 1.15, 1.97, and 2.30 g L-1), with four replicates and two plants per experimental plot. Plant height, number of leaves, stem diameter, and gas exchange (stomatal conductance, net photosynthesis, intercellular CO2 concentration, transpiration rate, instantaneous carboxylation efficiency, instantaneous water use efficiency, and intrinsic water use efficiency) were evaluated at 60 days after the beginning of irrigation with saline water. Salinity of irrigation water negatively affects the gas exchange of pomegranate seedlings. Foliar nitrogen fertilization up to 1.31 g L-1 improves plant height and number of leaves in pomegranate seedlings under salt stress. Foliar nitrogen fertilization up to 1.59 g L-1 increases the net photosynthesis of pomegranate seedlings.

RESUMO A salinidade é um dos estresses abióticos que afeta as trocas gasosas e o crescimento de romãzeira. Neste sentido, à aplicação de adubo nitrogenado via foliar poderá minimizar estes efeitos. Com isso, o objetivo do presente estudo foi avaliar o efeito da aplicação foliar com nitrogênio em mudas de romã irrigadas com águas salobra. O delineamento utilizado foi de blocos casualizados, em esquema fatorial incompleto (Composto Central de Box), sendo cinco condutividade elétrica da água - CEa (0,50; 1,15; 2,75; 4,35 e 5,00 dS m-1) e cinco doses de adubação nitrogenada via foliar - ANF (0; 0,33; 1,15; 1,97 e 2,30 g L-1), com quatro repetições. A salinidade da água de irrigação afeta negativamente as trocas gasosas de mudas de romãzeira. A adubação nitrogenada foliar até 1,31 g L-1 melhora o crescimento em altura e no número de folhas em mudas de romãzeira sob estresse salino. Adubação nitrogenada foliar até a dose de 1,59 g L-1 aumenta a fotossíntese das mudas de romãzeira.

ABSTRACT The quality of the seeds can have an interaction with other factors such as nitrogen fertilization (N), causing an impact on the yield of wheat (Triticum aestivum L). The objective of this study was to evaluate the vigor impacts of two lots of wheat seeds (High and Low Vigor) and their interaction with different doses of N (0, 50, 75, 100 and 125 kg ha-1) on wheat yield. The experiment was installed in the IPTA Yhovy, Canindeyú, Paraguay. It consisted of a randomized complete block experimental design, with three repetitions and bifactorial arrangement of treatments (Seed vigor x N doses). Initial aerial cover (IAC), number of tillers/plant (NTP), number of spikes per area (NSA), number of grains per spike (NGS), thousand seed mass (TSM) and grain yield (GY) were evaluated. The data were submitted to the normality test by Shapiro-Wilk, the statistical analysis was performed with ANAVA and Tukey's Test at 5%. The High Vigor seeds provided greater initial coverage to the crop and a greater number of spikes m2, in the number of tillers/plant and in the number of grains per spike, no impact was noted. The grain yield was positively affected by the high vigor of the seed, with a 40% higher average compared to the crop from low vigor seeds, on the other hand, with high vigor seeds a greater response to N doses was achieved, and the highest average (2,748 kg ha-1) was obtained with the dose of 100 kg ha-1 of N, while with low vigor seeds there was a positive response up to the dose of 75 kg ha-1 of N, with an average yield of 1,725 kg ha-1.

RESUMEN La calidad de las semillas puede tener interacción con otros factores como la fertilización con nitrógeno (N), provocando impacto en el rendimiento de trigo (Triticum aestivum L). El objetivo de este estudio fue evaluar los impactos del vigor de dos lotes de semillas de trigo (Alto y Bajo Vigor) y su interacción con diferentes dosis de N (0, 50, 75, 100 y 125 kg ha-1) sobre el rendimiento del trigo. El ensayo fue instalado en el IPTA Yhovy, Canindeyú, Paraguay. Tuvo un diseño experimental de bloques completos al azar, con tres repeticiones y arreglo bifactorial de tratamientos (Vigor de semillas x Dosis de N). Se evaluaron, cobertura aérea inicial (CAI), cantidad de macollos/planta (CMP), cantidad de espigas por área (CEA), cantidad de granos por espiga (CGE), peso de mil semillas (PMS) y el rendimiento de granos (RG). Los datos se sometieron a la prueba de normalidad por Shapiro-Wilk, el análisis estadístico se hizo con ANAVA y Test de Tukey al 5%. Las semillas de Alto Vigor proporcionaron mayor cobertura inicial al cultivo y mayor cantidad de espigas m2, en cantidad de macollos/planta y en número de granos por espigas no se notó impacto. El rendimiento de granos fue afectado positivamente por el alto vigor de la semilla, con una media 40% mayor frente al cultivo proveniente de semillas de bajo vigor, por otro lado, con semillas de alto vigor se obtuvo una respuesta mayor a las dosis de N, obteniéndose la media más alta (2.748 kg ha-1) con la dosis de 100 kg/ha-1 de N, mientras que con semillas de bajo vigor se tuvo una respuesta positiva hasta la dosis de 75 kg ha-1 de N, con una media de rendimiento de 1.725 kg ha-1.

ABSTRACT Adjustments in the nitrogen fertilization recommendation in wheat fields are essential to promote an increase in nitrogen (N) use efficiency by the crop. The real-time estimation of the nutritional demand of plants considering the spatial variability is one of the efficient ways to perform this adjustment. This study aimed to develop a model for the indication of topdressing nitrogen fertilization as a function of nutritional N demand using NDVI. Data from field experiments conducted in four regions of the State of Rio Grande do Sul, Brazil, during the 2015, 2017, 2018, and 2019 agricultural years using cultivars with significant sowing areas in the state, were used to construct the model. The analysis of the relationship between the amounts of N accumulated in the shoot and NDVI values allowed establishing a single model for different cultivars. The proposed model is sensitive to capturing regional edaphoclimatic differences and variability in N dynamics in cultivated areas. A consistent relationship was found between NDVI values and biomass and N content, which supported the generation of the topdressing N indication model for wheat. Therefore, the proposed model has the potential to maximize N use and grain yield, in addition to optimizing the economic return of the crop.

ABSTRACT Second-crop maize-ruzigrass (Urochloa ruziziensis) intercropping, nitrogen (N) fertilization, and high maize plant densities enhance biomass production and N cycling, which may favor soybean growth and yield in the following season. This study aimed to assess the effects of second-crop maize-ruzigrass intercropping, N top dressing, and maize plant density on straw production in autumn/winter, N cycling, and agronomic performance of soybean crops grown in succession. Field experiments were installed in the 2018/2019 and 2019/2020 seasons using a randomized complete block design with split-split plots and four replications. The following factors were investigated: cropping system (sole maize and maize intercropped with ruzigrass), N top dressing (0 and 80 kg ha-1), and maize plant density (40, 60, 80, and 100 thousand plants ha-1). Maize-ruzigrass intercropping improved straw yield (2,365 kg ha-1) and N cycling (50 kg ha-1), and increased soybean yield in the following season (232 kg ha-1). N fertilization of maize increased soybean grain yield by 180 kg ha-1. Maize plant density did not influence the performance of succeeding soybean crops, regardless of the growing season.

RESUMO O consórcio milho segunda safra com braquiária ruziziensis (Urochloa ruziziensis), adubação com nitrogênio (N) e alta densidade de plantas do milho aumentam a produção de biomassa e a ciclagem de N, o que pode favorecer o crescimento e a produtividade da soja na safra seguinte. Este estudo teve como objetivo avaliar os efeitos do consórcio milho segunda safra com Brachiaria ruziziensis, aplicação de N em cobertura e densidade de plantas de milho sobre a produção de palha no outono/inverno, ciclagem de N e desempenho agronômico da soja em sucessão. Os experimentos de campo realizados nas safras 2018/2019 e 2019/2020, em delineamento de blocos completos casualizados com parcelas subdivididas e quatro repetições, investigaram os seguintes fatores: sistema de cultivo (milho solteiro e milho consorciado com Brachiaria ruziziensis), cobertura de N (0 e 80 kg ha-1) e densidade de plantas de milho (40, 60, 80 e 100 mil plantas ha-1). O consórcio milho-Brachiaria ruziziensis melhorou a produtividade de palha (2.365 kg ha-1) e a ciclagem de N (50 kg ha-1) e aumentou a produtividade de soja em sucessão (232 kg ha-1). A adubação nitrogenada do milho aumentou a produtividade de grãos de soja em 180 kg ha-1. A densidade de plantas do milho não influenciou o desempenho da soja cultivada em sucessão, independentemente da safra.