In this study, we presented the most commonly employed net photosynthetic light-response curves (P N /I curves) fitted by the Solver function of Microsoft Excel. Excel is attractive not only due to its wide availability as a part of the Microsoft Office suite but also due to the increased level of familiarity of undergraduate students with this tool as opposed to other statistical packages. In this study, we explored the use of Excel as a didactic tool which was built upon a previously published paper presenting an Excel Solver tool for calculation of a net photosynthetic/chloroplastic CO 2 -response curve. Using the Excel spreadsheets accompanying this paper, researchers and students can quickly and easily choose the best fitted P N /I curve, selecting it by the minimal value of the sum of the squares of the errors. We also criticized the misuse of the asymptotic estimate of the maximum gross photosynthetic rate, the light saturation point estimated at a specific percentile of maximum net photosynthetic rate, and the quantum yield at zero photosynthetic photon flux density and we proposed the replacement of these variables by others more directly linked to plant ecophysiology.

No abstract

RESUMO -Avaliaram-se o fluxo de biomassa e as características estruturais do dossel de Panicum maximum cv. Mombaça sob pastejo de lotação intermitente, com os períodos de descanso (PD) definidos em função do tempo necessário para a expansão de 2,5; 3,5 e 4,5 novas folhas por perfilho (tratamentos). A pastagem foi dividida em cinco ou seis piquetes, conforme o tratamento, caracterizando o delineamento de casualização completa. Utilizaram-se cinco novilhos Holandês/Zebu por tratamento, que pastejaram durante seis dias em cada um dos piquetes correspondentes. Animais de equilíbrio foram adicionados, quando necessário, para garantir índice de área foliar residual próximo de 2,0, ao final do 6 0 dia de pastejo. Durante os PDs de três ciclos de pastejo, estimaram-se as taxas de aparecimento, alongamento e senescência foliares (TApF, TAlF e TSF, respectivamente), a taxa de alongamento das hastes (TAlH) e a taxa de acúmulo de forragem (TAF). No início e final de cada PD, estimaram-se: altura do dossel, massa seca de forragem verde (MSFV) e relação folha/colmo. Logo após cada período de pastejo, estimou-se a densidade populacional de perfilhos (DPP). As características mais afetadas pelos PDs foram TAlH e relação folha/colmo. O PD de 2,5 folhas foi o único a exercer algum controle sobre o alongamento das hastes. Observou-se ainda forte plasticidade do dossel em resposta aos PDs. A TAlF (7,6 cm/perf x dia) e a DPP (350 perf/m 2 ) nos piquetes sob menor PD e a TAlH (0,29 cm/perf x dia) naqueles sob maior PD constituíram-se componentes importantes da produção. O prolongamento do PD acarretou maior altura e maior MSFV por ciclo de pastejo, porém com proporção crescente de colmos, acarretando acentuada redução na relação folha/colmo. Palavras-chave: relação folha/colmo, taxa de alongamento foliar, taxa de alongamento das hastes, taxa de senescência foliar Morphophysiology of Panicum maximum cv. Mombaça Canopy under Intermittent Stocking Grazing of Three Rest PeriodsABSTRACT -The tissue flow and structural traits of Panicum maximum cv. Mombaça canopy were evaluated under intermittent stocking, with rest period (RP) defined in terms of the time required for the expansion of 2.5; 3.5 and 4.5 new leaves per tiller. The pasture treatment was divided into five or six paddocks (replicates) per treatment, observing a completely randomized design. One group of five Holstein-Zebu crossbred steers, as testers, grazed the paddocks of the respective treatment during six days. Put and taken steers were used, when necessary, to obtain a residual leaf area index (LAI) of about 2.0, by the end of the 6 th grazing day. During the RPs of three grazing cycles, leaf elongation rate (LER), leaf senescence rate (LSR), culm elongation rate (CER) and net herbage accumulation rate (NHAR) were estimated. By the beginning and end of each RP, the following structural variables were estimated: canopy height, green herbage dry matter (GHDM) and leaf/culm ratio. Tiller population density (TPD) was assessed after each grazing period. The variables CER and le...

In Northeastern Brazil, the sweet potato is cultivated in small farms, in a family farming systems, constituting themselves an alternative way for the generation of food, employment and income. This study aimed to assess the effect of cattle manure levels and biofertilizer concentrations on the sweet potato cultivar White Queen productivity. The experiment was carried out from March to September 2007 at the EMEPA Experimental Station in Lagoa Seca, Brazil. The experimental design was randomized blocks, in split split plot 6 x 4 x 2 + 1 scheme, with four replications. The plots consisted of cattle manure levels (0, 10, 20, 30, 40 and 50 t ha -1 ), the subplot of biofertilizer concentrations (0, 15, 30 and 45%) and the sub subplots consisted of methods of biofertilizer application, to the soil or leaves. Also, there was an additional control treatment using N, P and K mineral fertilizer. Commercial and total root productivity was evaluated. The levels of 30.8 and 31.2 t ha -1 of cattle manure were responsible for the highest commercial and total sweet potato root productivity (17.4 and 13.1 t ha -1 , respectively). Biofertilizer concentrations of 29 and 28%, applied to soil and to leaves provided, respectively, the greatest productivities of total roots (15.4 and 13.1 t ha -1 ), whereas concentrations of 30 and 27%, also applied to soil and leaves were responsible, respectively, for the highest commercial root productivity (11 and 9.7 t ha -1 ).

Physicochemical characteristics and antimicrobial activity of the extracts propolis of the

RESUMO-Para a produção de mudas de qualidade, é necessária a utilização de substratos com propriedades físicas, químicas e biológicas que condicionem a germinação adequada das sementes e o estabelecimento das mudas. Neste sentido, foi realizado um experimento no Centro de Ciências Agrárias, da Universidade Federal da Paraíba, com o objetivo de avaliar o crescimento e a composição mineral de mudas de mangabeiras (Hancornia speciosa) em substratos compostos por diferentes proporções de fibra de coco (0% a 40%), esterco bovino (0% a 25%), terra vegetal (25% a 70%) e 15% de areia, fertilizados com superfosfato triplo (0; 5,5 e 11 g dm -3 ). A terra vegetal e a fibra de coco exerceram efeitos benéficos às mudas com o aumento de suas proporções no substrato. A adição do esterco e do superfosfato triplo inibiu a produção de matéria seca e a área foliar das mudas. Houve aumento dos teores de nutrientes nas mudas com o aumento da concentração de esterco nos substratos. Pela estimativa dos resultados, o substrato que proporciona maior crescimento e composição mineral mais equilibrada nas mudas de mangabeira deve ser constituído por 14% de esterco, 56% de terra vegetal, 15% de fibra de coco, 15% de areia e 4 g dm -3 de superfosfato triplo. Termos para indexação: Hancornia speciosa, misturas, nutrição mineral. DEVELOPMENT AND NUTRITIONAL QUALITY OF HANCORNIA SPECIOSA SEEDLINGS CULTIVATED IN MIXTURE CONTAINING COCONUT FIBER AND FERTILIZED WITH PHOSPHORUSABSTRACT -In order to produce good quality seedlings it is necessary to use a mixture that presents appropriate physical, chemical and biological properties, which supplies the necessary conditions for the germination and the seedling's establishment. This experiment was carried out at the Agricultural Sciences Center, Paraíba Federal University (Brazil), whose objective was to evaluate the growth and the mineral composition of Hancornia speciosa seedlings in substrata composed by concentrations of coconut fiber from 0% to 40%, manure bovine from 0% to 25%, soil from 25% to 70%, sand 15% and triple superphosphate between 0 and 11 g dm -3 . The soil and coconut fiber had beneficial effects on the H. speciosa seedlings with the increase of its concentrations in the mixture. The addition of the manure and the doses of triple superphosphate provoked a decrease in the matter and in the foliate area in the H. speciosa seedlings. There was an increase of the nutrients content in the seedlings in which there was an increase of the manure concentration in the mixture. It is recommended to use the concentrations of 14% of manure, 56% of soil, 15% of coconut fiber, 15% of sand and 4 g dm -3 of triple superphosphate, for the maximum estimated values of growth and nutritional composition.

The aim of this study was to gain information on quality traits, mainly bacterial and somatic cell counts of bulk milk, produced by small- and medium-scale producers in a semiarid northeastern region of Brazil and to identify and characterize possible risk factors associated with those quality traits. A cross-sectional study was performed on 50 farms. Bulk milk samples were collected for bacterial and somatic cell counts. Additionally, information about farm demographics, general management practices, hygiene, and milking procedures was also obtained. Multivariable analysis using logistic regression was performed with predictors previously identified by univariate analysis using a Fisher's Exact test. Aerobic mesophilic bacteria counts varied from 3.59 log to 6.95 log cfu/mL, with geometric mean of 5.27 log cfu/mL. Mean total coliform count was 3.27 log (1.52 log to 5.89 log) most probable number (MPN)/mL, whereas mean thermotolerant coliforms was 2.38 log (1.48 log to 4.75 log) MPN/mL. A high positive correlation was observed between aerobic mesophilic bacteria and coliform counts. Although most farms met the standard for the current regulations for total bacteria (88%) and somatic cell counts (94%), nearly half of the producers (46%) would have problems in achieving the 2012 threshold limit for total bacteria count if no improvement in milk quality occurs. Mean value for staphylococci was 3.99 log (2.31 log to 6.24 log) cfu/mL, and Staphylococcus aureus was detected in 33 (66%) farms. Premilking teat-end wash procedure (odds ratio=0.191) and postmilking teat dip (odds ratio=0.67) were associated with lower aerobic mesophilic bacteria and Staphylococcus aureus counts in bulk milk, respectively. Considering that the farm characteristics in this study are representative of the semiarid northeastern region, these findings encourage further investigations for supporting intervention measures intended to improve the quality of milk produced by smallholders.

The physiological quality of cotton cultivar seeds (Gossypium hirsutum var. latifolium L.) was evaluated in laboratory by the simulation of water potentials with polyethyleneglycol-6000 (0.0; -0.2; -0.4; -0.6; -0.8 and -1.0 MPa), at 25ºC using germitest paper as substrate. A completely randomized design in a 4 × 6 factorial scheme with four replications of 50 seeds each was used. The studied variables were: germination percentage, first count of germination, germination velocity index, accelerated aging in water, electrical conductivity, humidity, vigor classification, radicle length and radicle/shoot length ratio. The effect of water stress on seed viability and on plantlet vigor was severe at potentials below -0.4 MPa. The 'CNPA 187 8H' cultivar was the least sensitive to the tested osmotic potentials, both in terms of germination and of vigor. The 'BRS-201' cultivar was mostly affected by the viability and vigor tests under water deficit conditions. Differential viability and vigor between cultivars were observed under the water stress levels. Key words: Gossypium hirsutum var. latifolium L., PEG-6000, vigor, water potential Germinação de sementes de cultivares de algodoeiro sob estresse hídrico induzido por polietilenoglicol-6000RESUMO: A qualidade fisiológica de sementes de cultivares de algodoeiro (Gossypium hirsutum var. latifolium L.) foi avaliada em laboratório pela simulação de potenciais hídricos com polietilenoglicol-6000 (0,0; -0,2; -0,4; -0,6; -0,8 e -1,0 MPa), na temperatura de 25ºC, em substrato papel germitest. O delineamento utilizado foi o inteiramente casualizado, em esquema fatorial 4 × 6, com quatro repetições de 50 sementes. As variáveis estudadas foram: porcentagem de germinação, primeira contagem da germinação e índice de velocidade de germinação, envelhecimento acelerado em água, condutividade elétrica, umidade, classificação de vigor (plântulas normais, fortes ou fracas), comprimento de radícula e relação radícula/parte aérea. O efeito do estresse hídrico na viabilidade das sementes e no vigor das plântulas foi severo a partir de -0.4 MPa. O cultivar CNPA 187 8H foi o menos sensível aos níveis de potenciais osmóticos testados tanto em termos de germinação, como de vigor. O cultivar BRS-201 foi o mais afetada nos testes de viabilidade e vigor em condições de déficit hídrico. Observou-se comportamento diferenciado em relação à viabilidade e vigor em diferentes níveis de estresse hídrico simulado por polietilenoglicol-6000. Palavras-chave: Gossypium hirsutum var. latifolium L., PEG-6000, vigor, potencial hídrico