Pasture Fertilization Research Articles

The LTAR Grazing Land Common Experiment at Platte River High Plains Aquifer.

The Long-Term Agroecosystem Research (LTAR) network of the United States Department of Agriculture (USDA) consists presently of 18 sites within the contiguous United States that are managed by the Agricultural Research Service (ARS) and its partners. The LTAR network focuses on developing national strategies for more efficient, resilient, and profitable agricultural production systems, improved environmental quality, and enhanced rural prosperity. The Platte River High Plains Aquifer (PRHPA) LTAR site is managed jointly by the University of Nebraska-Lincoln (UNL) and USDA-ARS and is one of the LTAR sites that conduct research on both integrated cropping and grazing systems. The PRHPA region encompasses multiple land resource areas and diverse agricultural production systems. The PRHPA sites, predominantly located in eastern Nebraska, are designated as an integrated system focused specifically on the region's dominant production practices of row crop (corn and soybean), managed pastures, and beef cattle production. Here, we focus on C3 cool-season smooth bromegrass (Bromus inermis Leyss.) pasture grazing systems under prevailing and alternative management practices for the region. The sites evaluate continuous and rotational grazing with and without pasture fertilization (prevailing practices). In an additional treatment, cattle are supplemented with dry distillers grains plus solubles, while manure supplies fertilization (alternative practice). Main measurements at the site evaluate plant and animal productivity, forage quality, greenhouse gas fluxes, and soil physical, chemical, and biological properties. This paper describes the regional characteristics of the PRHPA site, ongoing LTAR research related to pasture and livestock production, stakeholder engagement, and future research plans.

Co-Creating Strategies to Optimize Traditional Silvopastoral Systems through the Management of Native Trees in Caívas in Southern Brazil

The conservation of forest remnants in southern Brazil is closely related to historical land use, for example in systems such as caívas that occur within remnants of the Araucaria Forest and include livestock production and the extraction of yerba mate. Over the last decade, technologies adapted for these systems have been developed that promote a significant increase in animal productivity, without harming forest regeneration or the maintenance of the tree layer. However, the fertilization of pastures proposed in the technology has also promoted greater growth of native trees, with a consequent increase in shade levels. This, in turn, has affected the maintenance of pasture and yerba mate in the understory. Thus, this study sought to develop a methodology to adjust shade levels based on forest management that adheres to the limits permitted by current legislation. The objective was to evaluate the effect of tree management to maintain 50% shade levels on environmental indicators in a caíva that has been implementing pasture improvement technology since 2013. Native tree management occurred in 2020 and 2022 and the results were compared with data from the floristic survey of the area carried out in 2013. The results indicate that although the adoption of forest management to adjust shade levels reduced the density of individuals, it did not affect forest diversity, nor the basal area of the caíva tree layer. As such, it is possible to maintain pasture and yerba mate production in the area. Strategies like this are fundamental so that the forest landscape can continue to offer a source of production while also supporting environmental conservation.

ОРГАНИЧЕСКИЕ УДОБРЕНИЯ НА ОСНОВЕ ПОБОЧНЫХ ПРОДУКТОВ ЖИВОТНОВОДСТВА – РЕЗЕРВ В ПОВЫШЕНИИ БИОЛОГИЧЕСКОЙ ПРОДУКТИВНОСТИ ПАСТБИЩ

The main requirements for livestock wastewater used for irrigation and fertilization of cultivated pastures are presented. The use of bedless manure and livestock effluents as an organic fertilizer helps to increase the biological productivity of pastures and provides green, juicy fodder for livestock needs and environmental protection.

Cecal dilatation in cattle ingesting Megathyrsus maximus (syn. Panicum maximum) cv. Mombaça and cv. Tanzânia

Nine outbreaks of cecal dilatation are reported in cattle in rotationally-grazed pastures of Megathyrsus maximus during the rainy season with one day grazing and rest intervals of 23–28 days. Clinical signs, observed 6–24 h after entering the pasture, were inappetence, long periods in sternal recumbency, rough hair coat, arched back, tenesmus with difficult defecation, dry stools, reduced ruminal movements, intestinal tympany with right abdominal distention, and decreased milk production. The animals recovered 8–12 h after their removal from the pastures. All pastures were fertilized at 80–120 kg/ha of urea/year. In six farms, in addition to urea, chicken litter (CL) was also added. Water-soluble carbohydrates (WSC), non-fiber carbohydrates (NCF) and starch concentrations in the pastures causing tympany were higher (P < 0.05) than in control pastures. To demonstrate the relationship of the disease with fertilization of the pastures, a pasture of M. maximus was divided into five blocks of 16 m2 and each block subdivided into four plots each, totaling 20 plots. One plot of each block was randomly chosen for 1 of 4 different treatments: 1. fertilized with 8 t/ha of CL; 2. fertilized with 16 t/ha of CL; 3. fertilized with 180 kg/ha urea; 4. control without fertilization. In general, plots fertilized with urea or with CL had higher NFC and starch concentrations (p < 0,05) than the control plots. In another experiment a pasture of M. maximus was divided into 23 paddocks and rotationally grazed. Ten paddocks were fertilized with 180 kg/ha of urea and five fertilized with 8 t/ha of CL. The concentration of NFC and starch were significantly higher (p < 0.05) in the pastures fertilized with urea and with urea plus CL. These results suggest that cecal dilatation may be caused by the high concentrations of NFC and starch in the pastures fertilized with urea and/or poultry litter.

Grazing intensity and nitrogen fertilization timing to increase soil organic carbon stock and nitrogen in integrated crop-livestock systems

ABSTRACT Integrated crop-livestock systems (ICLS) foster synergistic relationships to increase nitrogen (N) cycling and soil organic carbon (SOC) accrual in agricultural setups. This study evaluated how the grazing intensity and N fertilization (rates and timing) affect both SOC and N fractions, and soil organic matter chemical composition in an ICLS managed under no-tillage in an Oxisol, six years after initiation. The ICLS was compared to a nearby pasture (PA) and a native forest (NF). The treatments consisted of two grazing intensities: Low Sward Height (LH) and High Sward Height (HH) were maintained with high and low stocking rates, respectively. The HH varied between 0.20 and 0.60 m, and LH between 0.10 and 0.30 m according to the plant forage species throughout the experiment. Fertilization using 200 kg ha -1 N-urea, not splitting up, was conducted at two timings, either at the winter pasture establishment (autumn), about 35 days after sowing or during the summer cash crop cycle (spring). Total N amount per year, including both phases, pasture and cash crop was the same for all treatments. The SOC and N contents were assessed in soil and particulate organic matter (POM), while carbon (C) and N stocks were specifically determined in the soil. Soil organic matter composition was characterized by FTIR. The combination of HH and N fertilization during the pasture phase increased the content of C from 36.1 to 39.9 ± 0.7 g C kg -1 and of N from 2.7 to 3.2 ± 0.1 g N kg -1 . The SOC stocks varied from 37.3 to 41.1 ± 0.7 Mg C ha -1 , and the N stocks from 2.1 to 3.3 ± 0.1 Mg N ha -1 at 0.0-0.10 m soil layer. The SOC content of the POM and the soil organic matter chemical composition determined by FTIR were mainly affected by the grazing intensity. The HH led to an increased in C content within the POM fraction, reaching values of 51.6 ± 1 and 49.2 g C kg -1 , respectively to N crop fertilization and N pasture fertilization. Land-use changed how organic functional groups were stored in soil organic matter fractions. The NF had a greater abundance of aliphatic and phenol in the MAOM, while pasture and ICLS systems had greater aliphatic in the POM fraction. In ICLS, SOC accrual was positively associated with more recalcitrant organic functional groups of phenol, aromatic, and carbonyl C-O. The HH increases SOC accrual, while N-fertilization on pasture ensures adequate nutrition of plants and animals during the winter ICLS phase, at the same time as providing greater residual N for subsequent cash crops through enhanced catalyzed by ruminants. Therefore, grazing and fertilization management strategies should be considered to promote sustainable agriculture intensification with ICLS.

Can N2 fixation by forage legumes build soil organic matter to rival fertilizer N in a tropical forest biome?

Fertilization of pastures with nitrogen (N) can increase animal productivity and may also increase the stocks of soil carbon (C). Recently stoloniferous forage legumes have been used to develop productive sustainable mixed pastures in the Atlantic forest biome. The objective of this study was to compare the impact over 24 years on soil C and N stocks of a productive N-fertilized pasture of Urochloa brizantha cv. Marandu with a mixed forage peanut (Arachis pintoi)-Marandu grass pasture introduced 8 years after an N-fertilized elephantgrass (Pennisetum purpureum) pasture. The pastures were rotationally stocked by Nellore cattle a green-forage allowance equivalent to 4% of body weight and animal performance was continuously monitored. Soil samples were taken at the start of the study and after 8 and 24 years of grazing and analyzed for total C and N and 13C abundance. In 8 years, the stocks of soil organic matter (SOM – 0-30 cm) increased by 4.4 Mg C and 0.58 Mg N ha−1 under the elephantgrass pasture and by 10.4 Mg C and 1.23 Mg N ha−1 under the Marandu grass pasture, both fertilized with 160 kg N ha−1 yr−1. Over the subsequent 16 years, SOM stocks under the Marandu grass fertilized with 120 kg N ha−1 and the mixed forage peanut-Marandu pasture which replaced elephantgrass attained similar stocks of soil C of 51.8 and 52.5 Mg C ha−1 respectively, approximately 12 Mg C greater than under the native vegetation. The 13C abundance of the soil samples indicated that the C4 grass roots made an insignificant contribution to soil C below 30 cm depth. The results show that the N2-fixing forage peanut was just as effective in accumulating SOM as an annual application of 120 kg N fertilizer ha−1 and indicated that after 24 years of these pastures there was little further SOM accumulation.

Characteristics of two Panicum maximum grass cultivars fertilized with ash from wood grown in tropical soils

It is estimated that the livestock sector accounts for about 40% of the value of global agricultural production. Livestock plays an essential role in maintaining food security as the sector contributes around 13% of calories and 28% of protein demands required by humans worldwide. Fertilization of tropical pastures with wood ash emerges as a sustainable practice that can contribute to better nutrient cycling, increased production, and reduced dependence on mineral resources. In this context, the aim of this study was to evaluate the production characteristics of two Panicum maximum grass cultivars fertilized with ash from wood grown in tropical soils of the Brazilian Cerrado. The experimental design was in randomized blocks in a factorial arrangement 5x2 with five doses of wood ash (0, 8, 16, 24, and 32 g kg-1) and two cultivars of Panicum maximum (cv. BRS Zuri and cv. Mombasa), with six replications. The experiment was carried out in 5 dm3 pots for 120 days. The wood ash used in the experiment comes from the combustion of eucalyptus (Eucalyptus sp.) logs in a boiler. The application of wood ash in acidic tropical soils increased leaf area, tillering, leaf dry mass, stem dry mass, and root volume in Mombasa and BRS Zuri cultivars of Panicum maximum grass, with maximum production at a dose of 32 g kg-1. The application of wood ash in acidic tropical soils offers potential as a sustainable strategy to increase production in forage production area for animal consumption in grazing, given the growing demand for beef. In addition, it properly and safely disposes of waste and recycles nutrients extracted by the crops.

Soybean growth and nitrogen accumulation by soybeans in response to desiccation times of Urochloa brizantha pasture and nitrogen fertilization

The desiccation time of high-biomass pasture and nitrogen (N) fertilization of pasture and soybean can influence the soybean sowing, establishment and growth. The objective of this study was to evaluate how the time of desiccation of the preceding pasture of Urochloa brizantha cv. BRS Piatã, cultivated at three levels of N, and by the soybean N fertilization affect soybean growth and N accumulation. Three N rates (0; 150 and 300 kg ha-1), broadcast as urea on the U. brizantha pasture were evaluated separately in each N level, every one considered as one experiment. In each experiment, five times of pasture desiccation were evaluated (60; 45; 30; 15, and 1 day before soybean sowing) and two levels of soybean N fertilization: 30 kg ha-1 (urea) broadcast at sowing or without N fertilization. A randomized complete block design with five replications was used. Early desiccation of U. brizantha pasture favors the establishment of soybean and promotes an increase in biomass and N accumulation in the vegetative stages, however these differences are not observed during the grain filling, regardless the soybean N fertilization. The soybean yield was not influenced by the desiccation time. N fertilization with 30 kg ha-1 at sowing intensifies soybean growth at the vegetative phase, but after full flowering, there were no effects on biomass and grain yield, independently of the desiccation time.

Influence of Slow- or Fast-Release Nitrogen in Xaraés Grass under Tropical Conditions

Nitrogen (N) is a nutrient used worldwide in pasture fertilization. However, it is a very volatile element. Furthermore, inappropriate use promotes environmental pollution and economic losses. The present study was carried out to evaluate the effects of the N source on the productivity and N utilization efficiency in Xaraés grass (Brachiaria brizantha cv. Xaraés) under tropical conditions. The randomized complete block design was used in a 3 × 2 × 4 factorial scheme: three seasons (rainy, dry, and transition), two N sources (fast-release = conventional urea, and slow-release = treated urea), and four N doses (0, 80, 160, and 240 kg N/ha/year). Forage accumulation per day differed (p &lt; 0.0001) with the season and N dose. The interaction between those showed a positive linear effect (p &lt; 0.0001) during the rainy season and transition. With increasing N doses, there was a linear increase in annual dry matter production and N accumulation. However, the N utilization efficiency (p &lt; 0.0001) was reduced. Nitrogen sources did not affect forage accumulation and N utilization efficiency. Therefore, it is not recommended to replace fast-release nitrogen fertilization (conventional urea source) with a urease inhibitor (slow-release N source), promoting benefits with lower production costs.

Manejo de irrigação, interceptação luminosa e nitrogênio no cultivo do capim Tanzânia

ABSTRACT Management of nitrogen fertilization and light interception of pastures contributes to forage production in regions with low water availability. Therefore, the objective was to evaluate the effect of different nitrogen doses and light interception levels on the growth of Panicum maximum cv. Tanzania under different irrigation managements. The experiment was carried out in a greenhouse, using a factorial scheme (5 x 2 x 2), corresponding to five irrigation depths (40, 60, 80, 100, and 120% of actual evapotranspiration), two canopy light interception levels (90 and 95%), and two nitrogen doses (300 and 600 kg N ha-1 year-1). The highest biomass production occurs under irrigation with 120% of evapotranspiration. However, the best structural characteristics (tillering and number of leaves) occur with 100% of evapotranspiration, regardless of nitrogen dose and light interception level. Interruption of growth with 95% of incident light and fertilization with 600 kg N ha-1 year-1 promoted greater tillering, number of leaves and leaf length, regardless of the irrigation level. Tanzania grass management with an interruption of growth with 95% of incident light, 600 kg N ha-1 year-1, and irrigation with 80% of actual evapotranspiration led to tillering and number of leaves only 11% lower than the values found in the other treatments irrigated with 100% of actual evapotranspiration. Interruption of growth with 95% of incident light and fertilization with 600 kg N ha-1 year-1 improve the performance of Tanzania grass under deficit irrigation.

Application of remote monitoring and ground-based sensing in pastoralism

The development and implementation of an innovative system applying digital aerospace technologies in pastoralism constitute one of the current trends in agricultural development designed to solve numerous problems associated with soil fertility restoration in grazing pastures. Here, a promising line of research is to explore the feasibility of using satellite systems for an overall nutrient yield assessment per hectare of grazing land. The present article describes a comprehensive approach to the optimization of pastoralism that is based on remote methods for assessing pasture fertility using unmanned aerial vehicles (UAVs) and artificial Earth satellites. An analysis of existing methodological approaches reveals that the formalization of prediction processes is complicated by the lack of a theoretical basis for creating appropriate model-algorithmic support. The data on vegetation index dynamics and the nutritional values of forage plants obtained by interpreting imagery from a UAV camera and the multispectral cameras of a satellite service, as well as data from a portable handheld nitrogen sensor, were compared with the actual nutritional values of pasture plants. The study results provide a means to optimize the grouping of grazing animals, taking into account the actual possibility of achieving an increase in live weight. The provided findings indicate the possibility of achieving an additional 11.06% increase in daily live weight gain in young sheep (Jalgin Merino) when keeping them in pasture areas having a vegetation index of at least 0.5. Remote monitoring based on satellite service allows more efficient use of pastures. Study shows a positive relationship between remote sensing NDVI and feed nutritional value. Animal grazing optimization provides an additional 11.06% increase in live weight gain.

Plant Growth Promoting Filamentous Fungi and Their Application in the Fertilization of Pastures for Animal Consumption

The diversity of fungi in different terrestrial and aquatic ecosystems has made it possible to explore their use as important tools in promoting plant growth and in managing plant diseases given their high potential to replace the use of synthetic chemical products (fertilizers and pesticides). Therefore, this review compiles information on the use of filamentous fungi in promoting plant growth, highlighting the most studied fungal genera for this purpose, such as Trichoderma, Penicillum, and Aspergillus. In addition, information is compiled on the promotion of forage grass growth using filamentous fungi, which could be a sustainable and lower-cost alternative in producing pastures to help raise animals.

Response of Pasture Nitrogen Fertilization on Greenhouse Gas Emission and Net Protein Contribution of Nellore Young Bulls.

This study aimed to evaluate the greenhouse gas (GHG) emission and net protein contribution (NPC) of Nellore young bulls grazing marandu palisade grass (Urochloa brizantha cv. Marandu) under three levels of pasture nitrogen (N) fertilization during backgrounding and finished on pasture or feedlot, based on concepts of sustainable intensification. The treatments were: System 1: pastures without N fertilizer during backgrounding, and animals finished on pasture supplemented with high concentrate at a rate of (20 g of concentrate per kg of body weight; P0N + PS); System 2: pastures fertilized with 75 kg N ha-1 year-1 during backgrounding and animals finished on feedlot fed a total mixed ration (TMR; P75N + F); and System 3: pastures fertilized with 150 kg N ha-1 year-1 during backgrounding, and animals finished on feedlot fed a TMR (P150N + F). During backgrounding, all pastures were managed under a continuous and put-and-take stock grazing system. All animals were supplemented with only human-inedible feed. Primary data from systems 1, 2 and 3, respectively, in the field experiment were used to model GHG emissions and NPC (a feed-food competitiveness index), considering the backgrounding and finishing phases of the beef cattle production system. Average daily gain (ADG) was 33% greater for the N fertilizer pastures, while carcass production and stocking rate (SR) more than doubled (P75N + F and P150N + F). Otherwise, the lowest GHG emission intensity (kg CO2e kg carcass-1) was from the P0N + PS system (without N fertilizer) but did not differ from the P75N + F system (p &gt; 0.05; pastures with 75 kg N ha-1). The main source of GHG emission in all production systems was from enteric methane. Moreover, NPC was above 1 for all production systems, indicating that intensified systems contributed positively to supply human protein requirements. Moderate N fertilization of pastures increased the SR twofold without increasing greenhouse gas emissions intensity. Furthermore, tropical beef production systems are net contributors to the human protein supply without competing for food, playing a pivotal role in the food security agenda.

N-fertilization of tropical pastures improves performance but not methane emission of Nellore growing bulls.

Grazing management and N-fertilizer have been reported to improve tropical forage productivity and quality, however, their effect on methane emission of grazing animals remains uncertain. Therefore, this study aimed to assess the effects of increasing application rates of nitrogen (N) fertilization of Marandu palisadegrass under continuous stocking on intake, digestibility, nitrogen balance, and enteric methane emissions of Nellore growing bulls. We hypothesized that changes in the forage nutritive value caused by N fertilization of pastures combined with adequate grazing management (e.g., greater crude protein [CP] and digestibility) would lead to an increase in animal productivity (e.g., greater average daily gain [ADG] and gain per area), and then, to a decrease in methane emission intensity. Treatments consisted of different annual application rates of nitrogen fertilization: 0, 75, and 150 kg N/ha using ammonium nitrate (32% N) as the nitrogen source. The experimental design was completely randomized, with three treatments and four replications (12 paddocks). Intake, digestibility, N balance, and methane emissions were measured in eight animals per treatment. CP intake, digestibility and N balance increased linearly with the increase in N fertilization (P < 0.05). In addition, stocking rate (SR) and ADG linearly increased from 1.75 animal unit (AU = 450 kg)/ha and 0.62 kg/d (0 kg N/ha) to 3.75 AU/ha and 0.82 kg/d (150 kg N/ha), respectively. Individual methane emissions nor methane emission intensity were affected by treatment with an average of 164.7 g/d and 199.7 g/kg ADG (P > 0.05). Annual N fertilization with ammonium nitrate between 75 and 150 kg N/ha in palisadegrass pastures under continuous stocking enhances animal performance per unit area yet not affecting neither methane production nor intensity.

Comparative Analysis of Pasture Soil Fertility in Semiarid Agro-Silvo-Pastoral Systems

Dryland pastures are usually on soils with a low fertility. However, a high spatial variability is apparent in pasture soils. In consequence, the application of inputs should be based on the particular characteristics of each field and their within-field variability. In this study, a comparative analysis of seven experimental fields (agro–silvo–pastoral ecosystems) in the southwest of the Iberian Peninsula was performed using a probabilistic and objective model. Some soil properties (the texture, cation exchange capacity, soil apparent electrical conductivity, organic matter, nitrogen, potassium and slope) measured at six sampling locations in each field were consolidated in the model. It was verified that the data fit the model and, later, a ranking of all the sampling locations and, consequently, a ranking of all the experimental fields according to the pasture soil fertility was established. Moreover, another output of the model was a ranking of the soil properties according to their influence on the soil fertility: the topographical property, the slope, was the most influential as it is related to the level of other important soil properties, as the textural components. Two fields, Cubillos and Grous, had the highest overall soil fertility levels because the soil samples in these fields were very fertile. However, some samples in the other five fields were also in the group of the most fertile, denoting the existence of an important spatial variability within each field. The proposed method is a rational way to improve the efficiency of the use of fertilisers by adjusting them to the soil pasture fertility.

THE ROLE OF TURKOMANS IN THE SELJUK-BYZANTINE RELATIONS IN THE PROCESS LEADING TO THE WAR OF MYRIOKEFALON

II. Kılıç Arslan Döneminde Anadolu’nun batı uçları Türkmenlerin yoğun yerleşim sahası haline gelmiştir. Konar-göçer yaşam tarzını sahip olan bu Türkmen toplulukları mevcut meraların hayvanları için yetersiz gelmeye başladığı zamanlarda Bizans arazisindeki verimli otlakları kullanmaya başlamışlardır. Ayrıca kendi başlarına üretemedikleri ürünleri temin etmek maksadıyla Bizans yerleşim yerine yağma akınları düzenlemişlerdir. Türkmenler, yaşam biçimlerinin etkisiyle ortaya koydukları bu faaliyetlerle farkında olmadan II. Kılıç Arslan’ın Bizans’a yönelik politikalarını olumsuz etkilemeye başlamıştır. İmparator Manuel, Türkmenlerin yol açtığı bu tahribattan II. Kılıç Arslan’ı sorumlu tutarak Selçuklular üzerine birçok kez sefer düzenlemiştir. Bu durum Selçuklular ile Bizans arasındaki ilişkilerin çatışma boyutuna ulaşmasına ve Miryokefalon Savaşı’na giden süreçte belirleyici rol oynamıştır.

Performance of soybean crop in response to palisadegrass pasture desiccation and nitrogen fertilization under integrated crop-livestock system

The desiccation (burn down) time of high-biomass pasture in no-tillage system and nitrogen (N) fertilization of pasture and soybean can influence the crop performance under crop-livestock system. The objective of this study was to evaluate the effect of desiccation times of palisadegrass pasture combined with three N fertilization levels of pasture and two N fertilization levels of soybean on crop yield, yield components and grain oil and protein concentration. Three N rates in the U. brizantha cv. BRS Piatã pasture were evaluated (0; 150 and 300 kg ha-1 of N as urea) in three different experiments. In each experiment, five pasture desiccation periods (60; 45; 30; 15 and 1 days before soybean sowing) and two levels of N fertilization of soybean (30 kg ha-1 of N distributed as urea at sowing + a control without urea) were evaluated. A randomized complete block design with five replications was used for each experiment. After statistical analysis of each experiment, a joint analysis of the three experiments was performed, allowing the comparison of the three rates of N in the pasture. The time interval between Urochloa brizantha pasture desiccation and soybean sowing did not influence soybean yield, yield components or the grain oil and protein concentrations, regardless of N fertilization of pasture and soybean. N fertilization of pasture induced a taller soybean plant height, insertion height of first pod, increased lodging, and reduced yield, but did not change the grain oil and protein concentration, regardless of the pasture desiccation time and N fertilization of soybean. Soybean grain yield was negatively affected by N fertilization of the crop, regardless of fertilization levels and desiccation times of the previous pasture

Soil bacterial community response to rhizoma peanut incorporation into Florida pastures.

Incorporating legumes is one option for improving pasture fertility, sustainability, and biodiversity. Diazotrophic microorganisms, including rhizobia that form symbioses with legumes, represent a small fraction of the total soil microbial community. Yet, they can offset nitrogen (N) fertilizer inputs through their ability to convert atmospheric N2 into plant-usable N via biological N2 fixation (BNF). This study used amplicon sequencing of 16S rRNA genes to investigate soil bacterial community composition and diversity in grazed 'Argentine' bahiagrass (Paspalum notatum Flügge) pastures where N fertilizer was supplanted with legume-derived N from BNF in some treatments. Treatments consisted of bahiagrass fertilized with (a) mineral N (224kg N ha-1 yr-1 ), (b) combination mineral N (34kg N ha-1 yr-1 ) and legume-derived N via cool-season clover (CSC) (Trifolium spp.) mix, or (c) combination mineral N (34kg N ha-1 yr-1 ) and legume-derived N via CSC mix and strips of Ecoturf rhizoma peanut (Arachis glabrata Benth.). Bradyrhizobium spp. relative abundance was 44% greater in the mixed pasture. Other bacterial genera with BNF or denitrification potentials were greater in pastures with legumes, whereas sequences assigned to genera associated with high litter turnover were greater in bahiagrass pastures receiving only mineral N. Soil bacteria alpha diversity was greater in pastures receiving 34kg ha-1 yr-1 N fertilizer application and the CSC mix than in pastures with the CSC mix and rhizoma peanut strips. Our results demonstrate soil microbial community shifts that may affect soil C and N cycling in pastures common to the southeastern United States.

Relationships between N, P, and K in corn biomass for assessing the carryover effects of winter pasture to corn

Pasture fertilization may influence the subsequent corn crop in integrated crop-livestock systems, but few tools exist to assess the likelihood and magnitude of this carryover effect. Our goals were to determine whether a previous pasture with N fertilization could supply adequate N nutrition to a succeeding corn crop and affect its P and K nutrition using the concept of N dilution curve and relationships between N, P, and K in corn shoot biomass. The experiment consisted in a winter grazed pasture followed by a corn crop in summer. Treatments were N fertilization of a black oat (Avena strigosa) winter pasture (0 and 200 kg N ha−1) as main plots and four sidedress N fertilization rates (0, 100, 200, and 300 kg N ha−1) applied to corn as sub-plots in a randomized complete block design with split-plot restriction. The N nutrition index, that is, the ratio of observed shoot N concentrations to critical N concentration determined by a critical N dilution curve, adequately identified situations of deficient N nutrition in corn following a pasture with or without N fertilization. This carryover effect from a winter pasture should therefore be accounted for in N fertilizer recommendations for corn in tropical soils. Corn P nutrition, based on critical P concentrations derived as a function of N concentration, was nearly optimal when no N was applied to the pasture, but it was less than optimal when N was applied. Although no critical K curves have been published, our results confirm that the relationship between shoot K and N concentrations varies with the level of N nutrition as does the relationship between shoot P and N concentrations. Our results confirm that the concept of critical N and P concentrations serves as a useful reference to assess the status of N and P nutrition during corn growth in tropical soils with the potential to improve nutrient management of corn following a pasture in an integrated crop-livestock system.

INFLUÊNCIA DA ADUBAÇÃO NO TEOR DE NITRATO NAS PASTAGENS E NO LEITE AO LONGO DO ANO NO OESTE DE SANTA CATARINA

The indiscriminate use without criteria of nitrogen fertilization can lead to an accumulation of nitrate in pastures, animal poisoning and potential increase in residual content of this compound in milk. The objective of this study was to determine the residual levels of nitrate throughout the year in pastures and milk from small farms in western Santa Catarina (SC) that use high levels of nitrogen fertilization. The experiment was carried out from April/2018 to March/2019 on 10 dairy farms in the municipality of Riqueza (SC). Two annual collections of water samples and monthly collections of pastures and milk were carried out, in addition to obtaining information on the property and management of pasture fertilization through a structured questionnaire. Nitrate was also evaluated in pastures using the diphenylamine test. Temperature and rainfall data were obtained daily by a weather station. The average amount of nitrogen fertilizer used in the properties was 654 ± 176 kg/ha/year. The average nitrate content in the drinking water of the animals was 1.5 ± 1.4 mg/L, in the pasture it was 270 ± 76 mg/kg DM, while in milk it was 2.0 ± 0.3 mg/L. There was seasonal variation with an increase in nitrate content in pastures and milk in autumn, a period of the experiment in which low rainfall was observed. It was concluded that despite being dairy properties with high use of nitrogen fertilization, safe milk is produced in terms of nitrate levels, even in times of the year with adverse climatic conditions. The diphenylamine test has a good ability to discriminate the nitrate content in pastures and can be indicated as a quick test to verify the presence of high levels of nitrate in the pasture.