O uso de determinadas fontes nitrogenadas, doses e formas de nitrogênio (N) pode aumentar a eficiência de uso de N (EUN) em soqueiras de cana-de-açúcar (Saccharum spp.), mantendo, em longo prazo, elevados índices de produtividade, lucro e proteção ao ambiente. Experimentos de campo e de casa-de-vegetação foram desenvolvidos com os seguintes objetivos: (i) avaliar o efeito do manejo do N-fertilizante e dos ciclos de soqueira da cultura na produtividade, parâmetros tecnológicos, acúmulo de biomassa, acúmulo e balanço de nutrientes e nas alterações dos atributos químicos do solo; (ii) avaliar a produção de biomassa seca, metabolismo e nutrição de plantas de cana-de-açúcar cultivadas em solução nutritiva, com suprimento exclusivo ou misto de nitrato (NO3-) e amônio (NH4+) como fontes de N; (iii) avaliar a EUN do 15N-nitrato (15NH4NO3), 15N-amônio (NH415NO3) e 15N-amida [(15NH2)2CO] aplicados na quarta soqueira de cana-de-açúcar em condições de campo; e avaliar a EUN do 15N-amônio e 15N-nitrato aplicados em mudas de cana-de-açúcar cultivadas em solução nutritiva. No campo, o N-fertilizante foi repetido nas mesmas parcelas experimentais (parcelas estáticas), em anos subsequentes (quatro ou cinco soqueiras) e o manejo de N-fertilizante, que incluiu fontes e doses de N, não influenciou na produtividade de colmos e de açúcar no local 1 (Latossolo Vermelho Amarelo distrófico - LVAd). Entretanto, no local 2 (também LVAd), o NA100 e o NAC100 [nitrato de amônio (NA) e nitrato de amônio e cálcio (NAC), ambos na dose de 100 kg ha-1 de N] foram os manejos mais vantajosos para a obtenção das maiores produtividades de colmo e de açúcar em soqueiras quando comparado aos demais tratamentos. No geral, nos dois locais, o NAC150 (150 kg ha-1 de N) proporcionou os maiores acúmulos de biomassa, N e K nas plantas. Além disso, enquanto o controle (sem adição de N) apresentou as menores produções de biomassa e acúmulos de nutrientes (com exceção ao P), o balanço de nutrientes do solo nesse tratamento foi relativamente neutro após anos de cultivo da cana-de-açúcar. Em condições controladas, plantas de cana-de-açúcar supridas exclusivamente com amônio apresentaram menor produção de biomassa, acúmulo de nutrientes e área foliar do que os outros tratamentos (supridos com combinações de NO3-/NH4+ e somente com nitrato), indicando que o uso exclusivo dessa forma de N não foi eficiente para sustentar o crescimento vegetal. A maior EUN foi obtida com o fornecimento exclusivo de nitrato, que também proporcionou maior produção de biomassa seca, área foliar, acúmulo de macronutrientes, atividade fotossintética e crescimento do sistema radicular. A utilização de 15N indicou que, no campo, não houve diferença na EUN pelas plantas devido à utilização do 15N-nitrato e 15N-amônio. Em contraste, a EUN do 15N-amônio foi maior que a do 15N-nitrato durante o 1º, 4º e 7º dia após a aplicação do fertilizante (DAAF), em condições controladas. Contudo, o uso do 15N-nitrato teve maior EUN nas raízes e planta inteira que o 15N-amônio no 15º DAAF. Isso indica que a cana-de-açúcar pode aproveitar eficientemente as duas formas minerais de N, embora o aproveitamento do amônio seja mais rápido. / The use of different fertilizers and rates of nitrogen (N) can increase the N use efficiency (NUE) in sugarcane ratoon (Saccharum spp.), sustaining high yield levels, profitability and environmental protection in long-term. Thus, field and greenhouse studies were performed with the following objectives: (i) evaluate the effect of fertilizer-N management and ratoon crop cycles on sugarcane yield, technological parameters, biomass accumulation, nutrient content, temporal variation in soil chemical properties and soil nutrient balance; (ii) evaluate the biomass production, metabolism and nutrient acquisition of sugarcane plants cropped in nutrient solution, with solely or combined supply of ammonium and nitrate as N sources; (iii) evaluate the NUE of 15N-ammonium (15NH4NO3), 15N-nitrate (NH415NO3), and 15N-amide [(15NH2)2CO] applied to sugarcane under field conditions and the NUE of 15N-ammonium and 15N-nitrate applied to seedlings sugarcane under nutrient solutions. In the field, N fertilizers were replicated in the same experimental plots (static plots) in subsequent years (four or five ratoons) and the management of N-fertilizer, which included fertilizers and N rates, resulted in lack of influence on cane and sucrose yield at Site 1 (Typic Hapludox). However, at Site 2 (also Typic Hapludox), the N treatments AN100 and CAN100 [ammonium nitrate (AN) and calcium ammonium nitrate (CAN), both at a rate of 100 kg N ha-1] provided the highest cane and sugar yield as compared to the remaining treatments. Overall, at both sites, CAN150 (150 kg N ha-1) resulted in the highest biomass accumulation and N and K content by sugarcane. In addition, while the control (no N added) had the lowest biomass accumulation and nutrient content (except for P), the soil nutrient balance in this treatment was relatively neutral, after years of sugarcane cultivation. Under controlled conditions, NH4+-fed plants presented lower biomass accumulation, nutrient content and leaf area than the other treatments (different NO3-/NH4+ ratios and NO3--fed plants), indicating that this N form, when applied solely, was not effective for the proper plant growth. The highest NUE was obtained with NO3--fed plants, which also had the highest production of dry biomass, leaf area, nutrient accumulation, photosynthetic activity, and growth of the root system. The use of 15N-nitrate and 15N-ammonium indicated that there was no difference in NUE by plants in the field. In contrast, the NUE of 15N-ammonium was greater than 15N-nitrate during the 1st, 4th and 7th day after fertilizer application (DAFA), under controlled conditions. However, the use of 15N-nitrate had greater NUE in roots and whole plant than 15N-ammonium in the 15th DAFA. It can be concluded that sugarcane can use both N forms although the recovery of NH4+ was faster than NO3-.

O sistema integração lavoura pecuária (ILP) atende muitas diretrizes para estabelecer um manejo sustentável de produção agropecuária. Consiste em integrar na mesma área, a produção agrícola e pecuária de forma que haja o cultivo de grãos e estabeleça uma pastagem para a criação de animais. O consórcio de milho com braquiária é uma tecnologia utilizada para se atingir os objetivos da ILP. Trata-se de técnica de cultivo de milho junto com a braquiária sem prejuízo ao milho, e que a braquiária possa se estabelecer na área após a colheita do milho. A eficiência da adubação nitrogenada (EAN) na cultura do milho é discutida na literatura em trabalhos que utilizaram fertilizantes marcados com 15N. Os dados são variados pelo motivo do nitrogênio ter dinâmica complexa no sistema produtivo. Trabalhos que avaliaram a EAN no consórcio de milho com braquiária são escassos na literatura internacional, e não se sabe quanto do fertilizante nitrogenado aplicado é absorvido pela planta forrageira, e se é necessário um aumento da dose para não ocorrer falta de nitrogênio neste sistema de produção. Esta tese foi realizada com os seguintes objetivos (i) avaliar a influência da braquiária no aproveitamento do fertilizante nitrogenado, em razão das formas de implantação do consórcio milho - braquiária utilizadas no Brasil, (ii) avaliar a eficiência do N proveniente de fertilizante de liberação gradual, (iii) verificar a possibilidade da aplicação a lanço de ureia revestida. A primeira pesquisa foi desenvolvida nas cidades de São Desidério-BA e Piracicaba-SP, e foi comprovado que a presença da braquiária não afetou a produtividade de milho nem a recuperação do 15N-fertilizante. As formas recomendadas para implantação do consórcio de milho com braquiária são: (i) braquiária semeada a lanço antes da semeadura do milho; (ii) braquiária no centro das entrelinhas de milho; (iii) braquiária junto com o fertilizante de semeadura do milho, (iv) braquiária junto com o fertilizante de cobertura incorporado nas entrelinhas. Não é necessário aumentar a dose do fertilizante nitrogenado em sistema de milho consorciado com braquiária, uma vez que a braquiária absorve no máximo 4,3 kg ha-1 do N-fertilizante. A segunda pesquisa foi realizada nas cidades de Taquarituba-SP e Uberlândia-MG, e demonstrou que a produtividade de milho e o acúmulo de N não variam com o uso de ureia de liberação controlada aplicadas a lanço e incorporada em relação à ureia comum. As ureias de liberação controlada não promovem maior recuperação do 15N-fertilizante pelo milho e pela braquiária em relação à ureia comum, nem a produção de biomassa da braquiária. O N do fertilizante absorvido pela braquiária consorciada com milho é menos de 1% de todo N acumulado no sistema, e no máximo 2% do N-fertilizante aplicado. As ureias de liberação controlada não viabilizam a aplicação a lanço, e dependem das mesmas condições climáticas que a ureia comum para obterem bom desempenho. / Crop-livestock integration system (CLI) attends many guidelines for establishing a sustainable agricultural production. CLI consists in integrating agricultural and livestock production in the same area, in order to establish a pasture for grazing animals after a grain production. Intercropping corn and palisadegrass is a technology used to obtain CLI objectives. In this technique the palisadegrass is cropped together with corn without affecting corn yield, and after harvest the palisadegrass grows in the area in order to form a pasture. Studies that evaluated nitrogen use efficiency (NUE) in maize in crop systems with labeled 15N-fertilizer shows varied data. This is due to nitrogen\'s complex dynamics in the production system. However, studies that evaluated NUE in corn intercropped with palisadegrass are scarce in the literature, and it is unknown how much of nitrogen fertilizer applied is uptake by the palisadegrass, and if an increase in nitrogen rate is necessary to avoid lack of nitrogen in production system. The aims of this thesis was to evaluate: (i) the influence of palisadegrass in the use of nitrogen fertilizer, according to forms of implantation of palisade grass used in Brazil, (ii) the efficiency of N from gradual release fertilizer,(iii) the viability of broadcast application of coated urea on intercropping system. The first study was conducted in the sites of Sao Desidério-BA and Piracicaba-SP, and it demonstrated that the presence of palisadegrass did not affect corn yield neither 15N-fertilizer recovery. Intercropping system can be established by the followings forms: (i) palisadegrass broadcasted before maize sown, (ii) placed between the rows of maize, (iii) palisadegrass applied together with corn fertilizer, (iv) with topdressing fertilizer in furrows. It is not necessary increase N rate in the intercropping system because palisadegrass uptakes at most of 4.3 kg ha-1 of N-fertilizer. The second research was conducted in two sites, Taquarituba-SP and Uberlândia-MG, and demonstrated that the use of coated urea did not differ in corn yield and N uptake in relation to the common urea, either when it was incorporated or broadcast applied. The coated urea neither promotes better recovery of the 15N-fertilizer by corn and braquiária in relation to the common urea, nor increases the palisadegrass biomass production. Nitrogen fertilizer uptake by palisadegrass represents less than 1% of total N uptake in the intercropping system, and a maximum of 2% of N-fertilizer applied The slow release urea does not enable the broadcast placement, and its efficiency depends upon the same climatic conditions of the common urea.

Σκοπός της παρούσας διδακτορικής διατριβής ήταν η μελέτη της δυναμικής του αζώτου σε καλλιέργεια γλυκού σόργου. Χρησιμοποιήθηκαν φυτά γλυκού σόργου [Sorghum bicolor (L) Moench] ποικιλίας Keller και πραγματοποιήθηκαν αφ’ ενός πειράματα στο πεδίο αφ’ ετέρου πειράματα σε πλαστικά δοχεία. Τα πειράματα πεδίου πραγματοποιήθηκαν σε αγρόκτημα του Πανεπιστημίου Πατρών, τις καλλιεργητικές περιόδους του 2004 και 2005, και περιλάμβαναν δύο χειρισμούς (βιολογική και συμβατική διαχείριση της γονιμότητας του εδάφους), με τρεις επαναλήψεις ο καθένας σε πλήρη τυχαιοποιημένη διάταξη. Τα αποτελέσματα των πειραμάτων πεδίου, έδειξαν ότι η βιολογική διαχείριση της γονιμότητας του εδάφους ευνόησε τη διαθεσιμότητα του εδαφικού νιτρικού αζώτου. Το 2004, μέχρι και την ολοκλήρωση της άνθησης, τα φυτά του βιολογικού χειρισμού συσσώρευσαν περισσότερο άζωτο από ό,τι τα φυτά του συμβατικού χειρισμού, αν και οι διαφορές δεν ήταν στατιστικά σημαντικές, εκτός από τη δεύτερη δειγματοληψία, όπου τα φυτά του συμβατικού χειρισμού συσσώρευσαν 2,69 N gm-2, ενώ για τα φυτά του βιολογικού χειρισμού η αντίστοιχη τιμή ήταν 5,12 N gm-2. Το 2005, η συσσώρευση αζώτου ακολούθησε παρόμοια πορεία μέχρι τα μέσα της άνθησης και οι διαφορές δεν ήταν στατιστικά σημαντικές, εκτός από τη τρίτη δειγματοληψία, όπου τα φυτά του συμβατικού χειρισμού συσσώρευσαν 3,61 N gm-2, ενώ για τα φυτά του βιολογικού χειρισμού η αντίστοιχη τιμή ήταν 4,61 N gm-2. H επίδραση εμβολίων Azospirillum brasilense, σε παραμέτρους αύξησης φυτών γλυκού σόργου και στην πρόσληψη αζώτου από τα φυτά, υπό διαφορετικά επίπεδα αζωτούχου λίπανσης μελετήθηκε σε πειράματα σε πλαστικά δοχεία. Το κάθε πείραμα περιλάμβανε πέντε χειρισμούς με τριάντα επαναλήψεις, έκαστος. Τα φυτά που εμβολιάστηκαν με Azospirillum brasilense και έλαβαν τη μισή ποσότητα αζώτου, έδωσαν 7,69 g ξηρής βιομάζας φυτό-1 στο τέλος του πρώτου πειράματος και 4,89 g ξηρής βιομάζας φυτό-1 στο τέλος του δεύτερου πειράματος, ενώ τα φυτά που δέχθηκαν πλήρη λίπανση αζώτου χωρίς εμβόλιο έδωσαν 2,39 και 2,04 g ξηρής βιομάζας φυτό-1 στο τέλος του πρώτου και δεύτερου πειράματος αντιστοίχως. Οι διαφορές των χειρισμών ανά πείραμα ήταν στατιστικά σημαντικές. Το συνολικό προσλαμβανόμενο άζωτο από τα φυτά που εμβολιάστηκαν με Azospirillum brasilense και έλαβαν τη μισή ποσότητα αζώτου ήταν 153,23 και 99,96 mg φυτό-1 στο τέλος του πρώτου και του δεύτερου πειράματος αντιστοίχως. Οι τιμές ήταν υψηλότερες σε σχέση με τις τιμές του συνολικού προσλαμβανόμενου αζώτου των φυτών των λοιπών και οι διαφορές ήταν στατιστικά σημαντικές. Τα αποτελέσματα των πειραμάτων έδειξαν υψηλή αξιοποίηση του εφαρμοζόμενου αζώτου των φυτών που εμβολιάστηκαν με Azospirillum. Τα αποτελέσματα υποδεικνύουν την βιωσιμότητα ενός βιολογικού συστήματος καλλιέργειας, όσον αφορά την κάλυψη των αναγκών των φυτών σε άζωτο. Η υψηλή αξιοποίηση του αζώτου από τα φυτά γλυκού σόργου, οδηγεί στη μείωση εφαρμογής αζωτούχων λιπασμάτων και συμβάλλει στη μείωση του κόστους καλλιέργειας, στη μείωση εκπομπών αερίων του θερμοκηπίου και στην μείωση διήθησης νιτρικών στο υπόγειο υδροφόρο ορίζοντα. / The aim of the present thesis was to study the nitrogen dynamics in sweet sorghum crop. Sweet sorghum plants [Sorghum bicolor (L) Moench] variety Keller were used, and field and experiments were conducted. Field experiments were conducted during 2004 and 2005 growing seasons at the experimental station of the University of Patras, Greece and there were two treatments (biological and conventional soil fertility treatment), in a randomized complete block experimental design with three replications. The results showed that biological soil fertility treatment favour soil nitrate nitrogen concentration. In 2004, until completion of blooming, nitrogen uptake was higher in plants cultivated on biological fertility treated soil than in them cultivated on conventional but the differences were not statistically significant, except in second sampling, which nitrogen uptake was 2,69 N gm-2 in plants cultivated on conventional fertility treated soil and it was 5,12 N gm-2 in plants cultivated on conventional fertility treated soil. In 2005, until half of blooming, nitrogen uptake was similarly ranged for both treatments but the differences were not statistically significant, except in third sampling, which nitrogen uptake was 3,61 N gm-2 in plants cultivated on conventional fertility treated soil and it was 4,61 N gm-2 in plants cultivated on conventional fertility treated soil. Τhe effect of Azospirillum brasilense inoculation on growth parameters and nitrogen uptake in sweet sorghum plants fertilized with various nitrogen levels, was studied during pot experiments. Each experiment was including five treatments and thirty replications of each. Plants inoculated with Azospirillum brasilense and receiving half amount of nitrogen fertilizer produced 7,69 g dry biomass plant-1 at the end of the first experiment and they produced 4,89 at the end of the second one, while plants receiving full amount of nitrogen fertilizer and no inoculation produced 2,39 and 2,04 g dry biomass plant-1 at the end of the first and second experiment, respectively. Differences among treatments in each experiment, were statistically significant. Total nitrogen uptake in Plants inoculated with Azospirillum brasilense and receiving half amount of nitrogen fertilizer was 153,23 and it was 99,96 mg plant-1 at the end of first and second experiment, respectively. Those plants showed higher nitrogen uptake than plants from each other treatment and the differences were statistically significant. Results showed that treatments which inoculated with Azospirillum brasilense were the most efficient in terms of nitrogen uptake. These results indicate that biological management provides an adequate nitrogen nutrition to sweet sorghum crop. High nitrogen efficiency in sweet sorghum plants leads in reduced applying nitrogen fertilization and contribute in reduced crop cost, in reduced emission of the greenhouse gas and in reduced leaching of NO3-N to ground water.

O presente trabalho foi desenvolvido na área experimental da ESALQ-USP, localizada no município de Piracicaba/SP, em um Latossolo Vermelho Amarelo, textura areno-argiloso. O experimento teve como objetivo estudar a dinâmica do N no sistema solo-planta da cultura do milho, sob implantação do sistema plantio direto, e, pela técnica do 15N, avaliar a lixiviação de nitrato à profundidade de 0,80 m, a eficiência de utilização do N e o efeito residual do fertilizante nas culturas subseqüentes. O projeto envolveu dois cultivos de milho e um de aveia preta, cultivada na entressafra. O delineamento experimental foi o de blocos casualizados (3x2), com 4 repetições. Os tratamentos consistiram de doses de nitrogênio, na forma de sulfato de amônio (60, 120 e 180 kg ha-1 de N) e uma testemunha, além dos parcelamentos (30 kg ha-1 de N na semeadura e o restante em cobertura; 60 kg ha-1 de N na semeadura e o restante em cobertura). A aplicação de sulfato de amônio enriquecido com 15N foi feita, na dose de 120 kg ha-1 de N, em subparcelas, previamente definidas, apenas no primeiro cultivo do milho. Foram feitas as seguintes avaliações: densidade de fluxo de água e de nitrato na profundidade de 0,80 m do solo (dose de 120 kg ha-1 de N); massa de 100 grãos; massa de matéria seca; teor de N; rendimento de grãos de milho; átomos % 15N nas plantas e solo; fração do N fertilizante na solução do solo na profundidade de 0,80 m, e no perfil do solo; balanço do N na sucessão de culturas; efeito residual do N fertilizante (aplicado no primeiro cultivo de milho) na aveia e no segundo cultivo de milho. Pelos resultados obtidos, concluiu-se que: a) a perda de nitrato total por lixiviação, a 0,80 m de profundidade, no 1º cultivo de milho, na dose de 120 kg ha-1 de N, foi de aproximadamente 96 e 68 kg ha-1, para os parcelamentos com 60 kg ha-1 e 30 kg ha-1 de N na semeadura, respectivamente, dos quais apenas 3 e 1 kg ha-1 foram provenientes do fertilizante nitrogenado; b) na dose 120 kg ha-1 de N, o tratamento com maior quantidade de N aplicado na semeadura (60 kg ha-1), no cultivo de milho do ano agrícola 2003/2004, proporcionou um maior aproveitamento do N do fertilizante (65%), em relação ao tratamento com a dose de 30 kg ha-1 na semeadura (45%) e que, para esse ano, a recuperação do N fertilizante pelo solo, na camada 0-0,80 m, para ambos os tratamentos, 60-60 e 30-90 kg ha-1, foi de 40 e 49%, respectivamente; c) Ainda referindo-se aos tratamentos 60-60 e 30-90 kg ha-1, do N remanescente do sulfato de amônio (120 kg ha-1), aplicado no primeiro ano agrícola (efeito residual), 3,72 e 1,79% foram utilizados pela aveia preta e 2,84 e 2,06% pelo milho cultivado no ano subseqüente (2004/2005), permanecendo no solo (camada 0-0,80 m), 30,19 e 33,47% após o cultivo de aveia preta e 16,79 e 17,91% após o segundo cultivo de milho, respectivamente, para os referidos tratamentos. / The general objective of this work was to study the dynamics of nitrogen in the soil-plant system of two maize crops with a black oats one in between, introducing the no-tillage system. Besides, fertilizing the first maize crop with 15N enriched nitrogen fertilizer, it was also objective of this work to assess the total and the derived from fertilizer nitrate leached at the depth of 0.8 m, the nitrogen use efficiency by the crops and the residual effect of the labeled nitrogen fertilizer. The experiment was carried in the experimental areas of ESALQ-USP in the country of Piracicaba (SP), in a yellow red latossol, sandy-loamy texture. The first maize crop was in 2003/2004 and the second one in 2004/2005. The experimental design was randomized blocks (3 x 2), with four replications. Treatments consisted of nitrogen (as ammonium sulphate) levels (60, 120 and 180 kg ha-1 of nitrogen) and the control, besides the splittings (30 and 60 kg ha-1 of nitrogen in the sowing and the rest in covering). The fertilization with 15N enriched ammonium sulphate in the first maize crop was made only for the level of 120 kg ha-1 of nitrogen, in subplots previously defined. The following measurements were carried out: soil-water and nitrate flux densities at the depth of 0.8 m (120 kg ha-1 of N); weight of 100 grains; weight of plant dry matter; nitrogen content; grain yield; total nitrogen; plant nitrogen use efficiency; fraction of the applied nitrogen in the soil solution at the depth of 0.8 m and in the soil profile; nitrogen balance in the crops succession; nitrogen residual effect in the black oat and the second maize crop. From the results, it could be concluded that: a) the leaching losses of total N, at the depth of 0,80 m, in the first maize crop, at the fertilization level of 120 kg ha-1 of N, were of 96 and 68 kg ha-1 for the splittings 60 and 30 kg ha-1 of N at sowing, respectively, from which only 3 and 1 kg ha-1 were derived from the nitrogen fertilizer; b) at the N fertilization level of 120 kg ha-1, the treatment with higher amount of applied N at sowing (60 kg ha-1) of the first maize crop (2003/2004) led to a higher plant N fertilizer recovery (65%) than the 30 kg ha-1of applied N at the sowing treatment (45%) and that, at the end of this crop cycle, the N fertilizer recovery by the 0-0,80 m soil layer, for 60-60 and 30-90 kg ha-1 treatments, were 40 and 49%, respectively; c) still for treatments 60-60 and 30-90 kg ha-1, from the total N applied in the first maize crop (120 kg ha-1), 3.72 and 1.79% were used by the black oats and 2.84 and 2.06% by the second maize crop, remaining in the soil (0-0.8 m layer), 30.19 and 33.47% after the black oats crop and 16.79 and 17.91% after the second maize crop, respectively for 60-60 and 30-90 kg ha-1 of N treatments.

Plicatula is a taxonomic group within of the genus Paspalum that contains interesting species considering their phenotypic diversity for forage traits, and some of these species have been improved through artificial interspecific hybridization. Nitrogen (N) is an important limiting factor to produce biomass. Forage legumes contribute with symbiotic N2 fixation and can increase biomass yield and the nutritive value of the pastures. The objectives of this thesis were: (i) evaluate dry matter yield (DMY), N use efficiency (NUE), nutritive value, cold tolerance and plant persistence in hybrids of Paspalum plicatulum x P. guenoarum subjected to N application rates, (ii) compare biomass yield and nutritive value of the grass–legume system to a grass–N fertilizer system, and (iii) select the best hybrids for new steps within the breeding program. The study was conducted from September 2015 to May 2017. The experimental design was a randomized complete block in split-plot arrangement with three replicates. Treatments were five N rates (0, 60, 120, 240, and 480 kg N ha-1 N), and one grass-legumes mixture (Trifolium repens + Lotus corniculatus) as whole plots, and six genotypes (1020133, 102069, 103084, 103061, P. guenoarum ecotype Azulão and Megathyrsus maximus cv. Aruana used as a control) as subplots. Nitrogen rates of 240 and 480 kg N ha-1 increased Total-DMY, Leaf-DMY, cold tolerance and persistence but decreased NUE. Higher NUE was obtained with N rates between 60 and 120 kg N ha-1. Total-DMY for grass-legume mixture was similar to the N rates of 60 and 120 kg N ha-1. Hybrid 1020133 had Total-DMY similar to Azulão and Aruana, as well as Leaf-DMY greater than Aruana. Hybrid 1020133 showed greater cold tolerance and exhibited greater NUE at 60 kg N ha-1 than the other genotypes. At the N rate of 480 kg N ha-1 increased crude protein (27%) and digestibility (4%) and decreased neutral (6%) and acid (7%) detergent fiber compared to the 0 kg N ha-1. Grass-legume mixture showed greater nutritive value compared to N-fertilized grass. Hybrid 103061 had greater crude protein and digestibility and lower neutral and acid detergent fiber than Azulão and Aruana. Therefore, there is opportunity to increase DMY, NUE, cold tolerance and plant persistence, and improve the nutritive value through genotype selection and N management. In addition, grass-legume mixture showed greater nutritive value than N-fertilized grass and can be an alternative practice to replace to the application of N fertilizer up to the rate of 120 kg N ha-1. Hybrids 1020133 and 103061 should be indicated for new studies, such as seed production and animal performance.

Plicatula is a taxonomic group within of the genus Paspalum that contains interesting species considering their phenotypic diversity for forage traits, and some of these species have been improved through artificial interspecific hybridization. Nitrogen (N) is an important limiting factor to produce biomass. Forage legumes contribute with symbiotic N2 fixation and can increase biomass yield and the nutritive value of the pastures. The objectives of this thesis were: (i) evaluate dry matter yield (DMY), N use efficiency (NUE), nutritive value, cold tolerance and plant persistence in hybrids of Paspalum plicatulum x P. guenoarum subjected to N application rates, (ii) compare biomass yield and nutritive value of the grass–legume system to a grass–N fertilizer system, and (iii) select the best hybrids for new steps within the breeding program. The study was conducted from September 2015 to May 2017. The experimental design was a randomized complete block in split-plot arrangement with three replicates. Treatments were five N rates (0, 60, 120, 240, and 480 kg N ha-1 N), and one grass-legumes mixture (Trifolium repens + Lotus corniculatus) as whole plots, and six genotypes (1020133, 102069, 103084, 103061, P. guenoarum ecotype Azulão and Megathyrsus maximus cv. Aruana used as a control) as subplots. Nitrogen rates of 240 and 480 kg N ha-1 increased Total-DMY, Leaf-DMY, cold tolerance and persistence but decreased NUE. Higher NUE was obtained with N rates between 60 and 120 kg N ha-1. Total-DMY for grass-legume mixture was similar to the N rates of 60 and 120 kg N ha-1. Hybrid 1020133 had Total-DMY similar to Azulão and Aruana, as well as Leaf-DMY greater than Aruana. Hybrid 1020133 showed greater cold tolerance and exhibited greater NUE at 60 kg N ha-1 than the other genotypes. At the N rate of 480 kg N ha-1 increased crude protein (27%) and digestibility (4%) and decreased neutral (6%) and acid (7%) detergent fiber compared to the 0 kg N ha-1. Grass-legume mixture showed greater nutritive value compared to N-fertilized grass. Hybrid 103061 had greater crude protein and digestibility and lower neutral and acid detergent fiber than Azulão and Aruana. Therefore, there is opportunity to increase DMY, NUE, cold tolerance and plant persistence, and improve the nutritive value through genotype selection and N management. In addition, grass-legume mixture showed greater nutritive value than N-fertilized grass and can be an alternative practice to replace to the application of N fertilizer up to the rate of 120 kg N ha-1. Hybrids 1020133 and 103061 should be indicated for new studies, such as seed production and animal performance.

Plicatula is a taxonomic group within of the genus Paspalum that contains interesting species considering their phenotypic diversity for forage traits, and some of these species have been improved through artificial interspecific hybridization. Nitrogen (N) is an important limiting factor to produce biomass. Forage legumes contribute with symbiotic N2 fixation and can increase biomass yield and the nutritive value of the pastures. The objectives of this thesis were: (i) evaluate dry matter yield (DMY), N use efficiency (NUE), nutritive value, cold tolerance and plant persistence in hybrids of Paspalum plicatulum x P. guenoarum subjected to N application rates, (ii) compare biomass yield and nutritive value of the grass–legume system to a grass–N fertilizer system, and (iii) select the best hybrids for new steps within the breeding program. The study was conducted from September 2015 to May 2017. The experimental design was a randomized complete block in split-plot arrangement with three replicates. Treatments were five N rates (0, 60, 120, 240, and 480 kg N ha-1 N), and one grass-legumes mixture (Trifolium repens + Lotus corniculatus) as whole plots, and six genotypes (1020133, 102069, 103084, 103061, P. guenoarum ecotype Azulão and Megathyrsus maximus cv. Aruana used as a control) as subplots. Nitrogen rates of 240 and 480 kg N ha-1 increased Total-DMY, Leaf-DMY, cold tolerance and persistence but decreased NUE. Higher NUE was obtained with N rates between 60 and 120 kg N ha-1. Total-DMY for grass-legume mixture was similar to the N rates of 60 and 120 kg N ha-1. Hybrid 1020133 had Total-DMY similar to Azulão and Aruana, as well as Leaf-DMY greater than Aruana. Hybrid 1020133 showed greater cold tolerance and exhibited greater NUE at 60 kg N ha-1 than the other genotypes. At the N rate of 480 kg N ha-1 increased crude protein (27%) and digestibility (4%) and decreased neutral (6%) and acid (7%) detergent fiber compared to the 0 kg N ha-1. Grass-legume mixture showed greater nutritive value compared to N-fertilized grass. Hybrid 103061 had greater crude protein and digestibility and lower neutral and acid detergent fiber than Azulão and Aruana. Therefore, there is opportunity to increase DMY, NUE, cold tolerance and plant persistence, and improve the nutritive value through genotype selection and N management. In addition, grass-legume mixture showed greater nutritive value than N-fertilized grass and can be an alternative practice to replace to the application of N fertilizer up to the rate of 120 kg N ha-1. Hybrids 1020133 and 103061 should be indicated for new studies, such as seed production and animal performance.

In der vorliegenden Studie wurden zwei Fragestellungen bearbeitet, die beide das Ziel verfolgen, die Stickstoff(N)-Ausnutzungseffizienz in landwirtschaftlichen Systemen zu steigern: 1) Hat die langjährige organische Düngung einen Einfluss auf den Abbau kürzlich applizierter organischer Dünger? Die Hypothese war, dass relevante Effekte nur bei schwer abbaubaren organischen Düngern auftreten während bei leicht abbaubaren organischen Düngern die Düngungshistorie keine Rolle spielt. 2) Können die hohen N-Bilanzüberschüsse im intensiven Freilandgemüsebau durch den Einsatz von Winterzwischenfrüchten (ZF) deutlich reduziert werden? Die Hypothese war, dass ZF die Bilanzüberschüsse der betrachteten zweijährigen Fruchtfolgen um mindestens 30 kg N / ha reduzieren. Die erste Hypothese wurde überprüft, indem der Abbau organischer Dünger in Böden, die sich in ihrer organischen Düngungshistorie unterschieden, gemessen wurde. Es wurden ein Topfversuch im Gewächshaus sowie ein Inkubationsversuch im Labor durchgeführt. Die Ergebnisse deuteten darauf hin, dass es Effekte der Historie auf den Abbau von Stallmist und Kiefernrinde gab, während es keine Effekte bei leicht abbaubarem Kohlmaterial gab. Daher wurde die Hypothese angenommen. Allerdings ergaben die beobachteten Effekte kein konsistentes Bild in Hinblick auf die Richtung der Effekte auf die Kohlenstoff(C)- und N-Mineralisierung und Effekte auf die Netto-N-Mineralisation waren generell sehr klein. Zur Überprüfung der zweiten Hypothese wurden an drei Standorten in Deutschland Feldversuche mit Gemüsefruchtfolgen und unterschiedlichen ZF durchgeführt. Die Ergebnisse ergaben, dass trotz der die mittleren Bilanzüberschüsse der Kontrollen (ohne ZF) von 217 kg N / ha die ZF die N-Bilanz im Mittel um nur 13 kg N / ha reduzierten. Daher wurde die Hypothese abgelehnt. Die Ergebnisse zeigten weiterhin, dass der verlustfreie Transfer der von der ZF aufgenommenen N-Menge an die Folgefrucht ein kritischer Schritt bei dieser Technik ist. / The current study dealt with two questions that target potential options to increase the nitrogen (N) use efficiency of agricultural systems: 1) Does long-term organic fertilization affect the decomposition of recently added organic fertilizers? The hypothesis was that effects only occur for recalcitrant organic fertilizers while for readily decomposable organic fertilizers, the fertilization history does not play a role. 2) Can the N balance surpluses in intensive field vegetable production systems be substantially reduced by cultivation of winter catch crops (CC)? The hypothesis was that the N balance surpluses of the investigated two-year crop rotations can be reduced by more than 30 kg N / ha. The first hypothesis was tested by applying organic fertilizers to soils that only differed in organic fertilization history. A greenhouse pot experiment and a laboratory incubation experiment were conducted. The results indicated that fertilization history had effects on the decomposition of farmyard manure and pine bark, not however on the decomposition of readily decomposable cabbage material. Hence, the hypothesis was accepted in that fertilization history effects depended on the type of fertilizer. However, fertilization history effects showed no consistent trend with respect to increase or decrease in carbon (C) and N mineralization and the effects on net N mineralization were minor in magnitude. The second hypothesis was tested by performing field experiments at three sites in Germany. Vegetable crop rotations were set up, testing different types of CC. The results suggested that in spite of high N surpluses in the control treatments (no CC) of 217 kg N / ha, CC reduced the N balance surplus on average by only 13 kg N / ha. Hence, the hypothesis was rejected. The findings further indicated that the transfer of N taken up by the CC to the succeeding crop is a critical step when adopting this technique.

Stickstoffdüngung und Bodenbewirtschaftung sind die Hauptquellen für Treibhausgase aus Anbausystemen. Dennoch sind diese Maßnahmen in Ackerbaubetrieben unerlässlich. In Anbetracht der Notwendigkeit, rasch Maßnahmen gegen den Klimawandel zu ergreifen, ist es notwendig Minderungspotentiale und Kosten in diesen Betrieben zu ermitteln und vergleichen. Es wurden Fallstudien in den USA, in Brasilien und in Deutschland durchgeführt, wobei jeweils eine Kultur in jeder Region untersucht wurde. Wissenschaftliche Literatur und Fokusgruppen mit lokalen Experten wurden genutzt, um realistische Ergebnisse zu generieren, die den lokalen Kontext abbilden. Diese Arbeit zeigt, dass die Wirtschaftlichkeit der Minderungsstrategien von dem betrachteten Zeithorizont abhängt, der sich aus der Kohlenstoffdynamik im Boden ergibt. Kurzfristig bieten Strategien, die die Kohlenstoffbindung fördern, ein größeres Minderungspotenzial, was jedoch langfristig nicht zutrifft. Kurzfristig wurden in Brasilien und den USA die geringsten Minderungskosten durch die Optimierung der Stickstoffdüngung erreicht. Diese Kosten sind negativ, was bedeutet, dass die Anwendung dieser Strategien, nicht nur ihre Emissionen, sondern auch ihre Kosten senken würden. Weitere kosteneffiziente Strategien waren die Verringerung der Bodenbearbeitungsintensität und Zwischenfrüchte, die in allen Fällen mit vergleichbaren Minderungskosten durchführbar waren und die Kohlenstoffbindung fördern. Der Einsatz von Hemmstoffen schließlich, der in den USA und in Brasilien möglich war, hatte die höchsten Minderungskosten. Langfristig betrachtet stiegen die Minderungskosten von Strategien mit Kohlenstoffbindung an und waren ähnlich hoch oder höher als bei Strategien ohne Kohlenstoffbindung. Da in allen Fällen dieselbe Methodik angewandt wurde, sind die Ergebnisse vergleichbar. Darüber hinaus sind die Ergebnisse zwar spezifisch für den Kontext, in dem sie berechnet wurden, sie liefern jedoch Erkenntnisse für ähnliche Regionen. / Nitrogen fertilization and soil management are the main sources of greenhouse gases from cropping systems. Yet these operations are essential on arable farms. Considering the need to take quick action against climate change, it is necessary to understand which mitigation potentials and cost can be attained in these farms and how they compare. Case studies in the USA, Brazil and in Germany were conducted, assessing one crop in each region. Scientific literature and focus groups with local experts were used to generate realistic results which depict the local context. This thesis identified that the economics of the mitigation strategies depended on the time horizon considered, which results from the carbon dynamics in the soil. In the short term, strategies promoting carbon sequestration offer a larger mitigation potential, yet this is not valid in the long term. In the short term, the lowest mitigation costs were attained by optimizing the nitrogen rate, feasible in the USA and Brazil. These costs are indicated to be negative, implying that adopting the strategy would not only lower emissions, but also reduce their costs. The next most cost efficient strategies were the reduction of the tillage intensity and cover crops, which were feasible in all cases with comparable mitigation costs and promote carbon sequestration. Lastly, the adoption of inhibitors, feasible in the USA and in Brazil, had among the highest mitigation costs. Assuming the long term, the mitigation costs of strategies with carbon sequestration increased, becoming similar to or higher than strategies without carbon sequestration. By applying the same methodology in each case, the results are comparable. Moreover, while the findings are specific to the context in which they were calculated, they provide insights for similar regions.