Reverse osmosis (RO) desalination plants enable the production of high-quality freshwater from seawater, explaining the increasing global use of this technology. However, a major operational challenge for RO is biofouling, caused by excessive biomass accumulation. Membrane fouling simulators (MFSs), downsized membrane systems, were demonstrated to be suitable for biofouling studies using tap water. There is a need to investigate biofouling using natural seawater. The seawater MFS studies involved (i) an exploratory study to evaluate the MFS setup, (ii) long-term operation without feed water nutrient dosage, (iii) impact of nutrient concentration, and (iv) a comparison of biofouling development with freshwater. MFSs were operated parallel at constant feed flow (0.2 m/s), with feed spacer and RO membrane, at varying biodegradable organic nutrient concentrations (0, 50, and 200 µg C/L). The relative pressure drop (RPD) was monitored over time, and biofilm development was characterized through the MFS window applying optical coherence tomography (OCT). Results demonstrated for seawater that (i) the developed setup had a reliable operation and provided reproducible data, (ii) biofouling development presented a minimal effect when nutrient concentration was quadrupled, (iii) there was no correlation between the nutrient concentration and growth rate for seawater experiments, suggesting biofilm development under conditions close to the maximum growth rate. Compared to tap water at the same nutrient concentrations, seawater showed much faster biofilm development, pressure drop increase, and strongly different biofilm morphology. This research provides new insights, new research directions and underlines the importance of doing MFS research with natural seawater.

O aprimoramento das práticas agronômicas e a utilização de alta tecnologia nas lavouras contribuiu para os aumentos significativos na produtividade das culturas e, pode ter alterado a dinâmica de absorção e partição dos nutrientes pelas plantas. As recomendações oficiais de adubação para a cultura de milho no Brasil estão baseadas no teor crítico do nutriente no solo e são provenientes de literaturas mais antigas. Por serem dinâmicos, os fatores que interagem em um sistema de produção agrícola podem ser melhor estudados através de modelos matemáticos. A técnica de modelagem em agricultura pode expandir a compreensão das interações que ocorrem no sistema solo-planta-atmosfera. Sendo assim, o objetivo deste estudo é propor um modelo para o cálculo de recomendação de adubação da cultura de milho, a partir da modelagem da marcha de absorção de nutrientes, da evapotranspiração potencial da cultura e, da partição dos nutrientes nas plantas, levando em consideração a taxa de absorção de cada nutriente para cada genótipo em um determinado sistema de produção. O modelo proposto considera que a recomendação de adubação deve ser realizada com base na variação temporal da taxa de absorção de nutrientes, a qual define melhor a demanda da cultura, em comparação com o teor crítico dos nutrientes no solo. Para a validação do modelo, sugere-se um ensaio de campo comparando as metodologias. / The improvement of agronomic practices and the use of high technology in field crops contributed for their significant increases in productivity, and could also have altered the dynamics of nutrient uptake and partition by the plant. Official recommendations for fertilizer applications to the maize crop in Brazil are based on the critical soil nutrient content and are relatively outdated. Since the factors that interact in an agricultural production system are dynamic, mathematical modeling turns out to be an appropriate tool for these studies. Agricultural modeling can expand our knowledge about the interactions prevailing in the soilplant- atmosphere system. In this way, the objective of this study is to propose a model for fertilizer recommendation of the maize crop, based on modelling nutrient uptake, potential evapotranspiration of the crop, and the partition of nutrients in the plant, taking into account the nutrient uptake rate of each genotype in a given production system. The proposed model considers that the fertilizer recommendation should be made based on the temporal variation of the uptake rate, which should better define crop needs in relation to the classic recommendation based on the critical soil nutrient content. To validate the model an experiment is suggested to compare methodologies.

As áreas destinadas à cultura de cana-de-açúcar estão concentradas em áreas de Cerrado, que são solos ácidos, com elevada saturação por alumínio e baixa saturação por bases. Para correção destas características, faz-se o uso de corretivos e fertilizantes no momento da implantação da cultura. Embora a toxidez por alumínio seja uma das mais sérias limitações ao crescimento de plantas em solos ácidos, há uma carência de estudos relacionando-a com a cultura de cana-de-açúcar. Com base nisto, o objeto deste trabalho foi avaliar o efeito da aplicação de calcário e gesso sobre o estado nutricional de quatro cultivares de cana-de-açúcar, distintas quanto à exigência nutricional, na fase de perfilhamento da cultura. Para tanto, desenvolveu-se experimento em casa de vegetação com vasos contendo 4 kg de amostra de solo, com saturação por alumínio de 29%, como substrato, com os seguintes tratamentos: 1) aplicação de calcário, 2) aplicação de gesso, e 3) controle, sem adição de calcário e gesso. Os cultivares utilizados foram: IACSP95-5000, IACSP94-2094, SP80-3280 e IAC95-3028. Após adição dos tratamentos, as amostras de solo foram incubadas por 45 dias. Para os materiais vegetais, mini-toletes de gema única das cultivares foram pré-brotados, crescidos por 90 dias e transplantados para os vasos, para os respectivos tratamentos. As plantas foram adubadas com macro e micronutrientes e cultivadas por 60 dias. Os tratamentos foram caracterizados quanto aos atributos químicos para avaliação da fertilidade após a incubação e após a coleta das plantas. Nas plantas, foram feitas avaliações de: clorofila, flavonoides, índice de balanço do nitrogênio (NBI), concentração de alumínio e dos nutrientes e produção de matéria seca de folha, colmo e raiz. Enquanto o tratamento gesso não diferiu do controle, o tratamento calcário foi efetivo para correção da reação da amostra de solo, com elevação dos valores de pH e saturação por bases, e redução da saturação por alumínio e acidez total, além do aumento nos teores de Ca e Mg. A adubação NPK+micro foi efetiva para aumentar os teores de P e K dos substratos de todos os tratamentos. Nas plantas, para todos os cultivares, os índices de clorofila, flavonoides e NBI foram mais adequados no tratamento calcário, em relação ao controle e ao gesso. A produção de matéria seca total e das partes das plantas, de modo geral, foi maior para a IACSP95-5000, intermediaria para a IACSP35-3028 e menor para a IACSP94-2094 e SP80-3280. Quanto aos tratamentos, não houve efeito do calcário e gesso sobre a produção de matéria seca de folha, contudo, houve aumento de produção de matéria seca de colmo e raiz pelo calcário, na cultivar IACSP95-5000. Independente do tratamento, as cultivares apresentaram concentração de alumínio superior a 5000 mg kg-1 nas raízes e inferiores a 360 e 160 mg kg-1 nas folhas e colmos, respectivamente, evidenciando que o Al foi acúmulo nas raízes das plantas. De modo geral, as concentrações de macro e micronutrientes variaram com os tratamentos e cultivares, porém sem valores altos e baixos extremos. Concluiu-se que a cultivar IACSP95-5000 tem maior potencial de produção em resposta à aplicação de calcário e que a saturação de alumínio de 29% não apresenta efeito negativo sobre a produção de matéria seca, exceto da cultivar IACSP95-5000, e estado nutricional das cultivares de cana-de-açúcar / The agricultural field for the cultivation of sugarcane are concentrated in areas of Cerrado, which are acidic soil with high aluminum saturation and low base saturation. For the correction of these characteristics, the use of correctives and fertilizers are needed. Although in acid soils the aluminum toxicity is one of the most serious limitations to the plant growth, there is a lack of studies on the effects of aluminum on sugarcane crop. Based on this, the object of this work was to evaluate the effect of application of limestone or gypsum on the nutritional status of four cultivars of sugarcane, with different nutritional requirement, at the tillering stage of crop. A pot experiment was developed at greenhouse condition. Pots containing 4 kg of a soil, with 29% of aluminum saturation, as substrate were treated with: 1) limestone, 2) gypsum, and 3) control without lime and gypsum application. The IACSP95-5000, IACSP94-2094, SP80-3280, and IAC95-3028 cultivars were tested. After the addition of the treatments, the soil was incubated for 45 days. For plant materials, mini stem cuttings of cultivars were germinated, grown by 90 days and transplanted to pots, for the respective treatments. The plants were fertilized with macro and micronutrients and cultivated along 60 days. The treatments were characterized with regard to chemical attributes for fertility assessment, both after soil incubation and after collecting plants. In plants, chlorophyll, flavonoids, nitrogen balance index (NBI), aluminum and nutrient concentrations, and production of total, leaf, stem and root dry matter were evaluated. While the gypsum treatment did not differ from the control, the limestone treatment was effective for the correction of soil reaction, with increasing the pH value and base saturation, and lowering the aluminum saturation and total acidity, besides increasing the levels of Ca and Mg. In plants, for all cultivars, the contents of chlorophyll, flavonoids and NBI were improved by limestone treatment, comparing to control and gypsum. Generally, the IACSP95-5000 cultivar had higher total plant parts dry matter production, following by IACSP35-3028 with an intermediate production, and by IACSP94-2094 and SP80-3280 with lower production. For treatments, there was no effect of limestone and gypsum on the production of leaf dry matter, however limestone increased the dry matter production of stem and root by IACSP95-5000. Regardless of treatment, the cultivars showed aluminum concentration greater than 5000 mg kg-1 in the roots, and less than 360 and 160 mg kg-1, respectively, in leaves and stems, showing that the Al was accumulated in the roots of plants. In General, the concentrations of macro and micronutrients varied with the treatments and cultivars, however without extreme high and low values. It was concluded that the cultivar IACSP95-5000 has greater potential production in response to the limestone application, and that the aluminum saturation of 29% poses no negative effect on dry matter production, except of the cultivar IACSP95-5000, and on nutritional status of the studied sugarcane cultivars

O aprimoramento das práticas agronômicas e a utilização de alta tecnologia nas lavouras contribuiu para os aumentos significativos na produtividade das culturas e, pode ter alterado a dinâmica de absorção e partição dos nutrientes pelas plantas. As recomendações oficiais de adubação para a cultura de milho no Brasil estão baseadas no teor crítico do nutriente no solo e são provenientes de literaturas mais antigas. Por serem dinâmicos, os fatores que interagem em um sistema de produção agrícola podem ser melhor estudados através de modelos matemáticos. A técnica de modelagem em agricultura pode expandir a compreensão das interações que ocorrem no sistema solo-planta-atmosfera. Sendo assim, o objetivo deste estudo é propor um modelo para o cálculo de recomendação de adubação da cultura de milho, a partir da modelagem da marcha de absorção de nutrientes, da evapotranspiração potencial da cultura e, da partição dos nutrientes nas plantas, levando em consideração a taxa de absorção de cada nutriente para cada genótipo em um determinado sistema de produção. O modelo proposto considera que a recomendação de adubação deve ser realizada com base na variação temporal da taxa de absorção de nutrientes, a qual define melhor a demanda da cultura, em comparação com o teor crítico dos nutrientes no solo. Para a validação do modelo, sugere-se um ensaio de campo comparando as metodologias. / The improvement of agronomic practices and the use of high technology in field crops contributed for their significant increases in productivity, and could also have altered the dynamics of nutrient uptake and partition by the plant. Official recommendations for fertilizer applications to the maize crop in Brazil are based on the critical soil nutrient content and are relatively outdated. Since the factors that interact in an agricultural production system are dynamic, mathematical modeling turns out to be an appropriate tool for these studies. Agricultural modeling can expand our knowledge about the interactions prevailing in the soilplant- atmosphere system. In this way, the objective of this study is to propose a model for fertilizer recommendation of the maize crop, based on modelling nutrient uptake, potential evapotranspiration of the crop, and the partition of nutrients in the plant, taking into account the nutrient uptake rate of each genotype in a given production system. The proposed model considers that the fertilizer recommendation should be made based on the temporal variation of the uptake rate, which should better define crop needs in relation to the classic recommendation based on the critical soil nutrient content. To validate the model an experiment is suggested to compare methodologies.

As áreas destinadas à cultura de cana-de-açúcar estão concentradas em áreas de Cerrado, que são solos ácidos, com elevada saturação por alumínio e baixa saturação por bases. Para correção destas características, faz-se o uso de corretivos e fertilizantes no momento da implantação da cultura. Embora a toxidez por alumínio seja uma das mais sérias limitações ao crescimento de plantas em solos ácidos, há uma carência de estudos relacionando-a com a cultura de cana-de-açúcar. Com base nisto, o objeto deste trabalho foi avaliar o efeito da aplicação de calcário e gesso sobre o estado nutricional de quatro cultivares de cana-de-açúcar, distintas quanto à exigência nutricional, na fase de perfilhamento da cultura. Para tanto, desenvolveu-se experimento em casa de vegetação com vasos contendo 4 kg de amostra de solo, com saturação por alumínio de 29%, como substrato, com os seguintes tratamentos: 1) aplicação de calcário, 2) aplicação de gesso, e 3) controle, sem adição de calcário e gesso. Os cultivares utilizados foram: IACSP95-5000, IACSP94-2094, SP80-3280 e IAC95-3028. Após adição dos tratamentos, as amostras de solo foram incubadas por 45 dias. Para os materiais vegetais, mini-toletes de gema única das cultivares foram pré-brotados, crescidos por 90 dias e transplantados para os vasos, para os respectivos tratamentos. As plantas foram adubadas com macro e micronutrientes e cultivadas por 60 dias. Os tratamentos foram caracterizados quanto aos atributos químicos para avaliação da fertilidade após a incubação e após a coleta das plantas. Nas plantas, foram feitas avaliações de: clorofila, flavonoides, índice de balanço do nitrogênio (NBI), concentração de alumínio e dos nutrientes e produção de matéria seca de folha, colmo e raiz. Enquanto o tratamento gesso não diferiu do controle, o tratamento calcário foi efetivo para correção da reação da amostra de solo, com elevação dos valores de pH e saturação por bases, e redução da saturação por alumínio e acidez total, além do aumento nos teores de Ca e Mg. A adubação NPK+micro foi efetiva para aumentar os teores de P e K dos substratos de todos os tratamentos. Nas plantas, para todos os cultivares, os índices de clorofila, flavonoides e NBI foram mais adequados no tratamento calcário, em relação ao controle e ao gesso. A produção de matéria seca total e das partes das plantas, de modo geral, foi maior para a IACSP95-5000, intermediaria para a IACSP35-3028 e menor para a IACSP94-2094 e SP80-3280. Quanto aos tratamentos, não houve efeito do calcário e gesso sobre a produção de matéria seca de folha, contudo, houve aumento de produção de matéria seca de colmo e raiz pelo calcário, na cultivar IACSP95-5000. Independente do tratamento, as cultivares apresentaram concentração de alumínio superior a 5000 mg kg-1 nas raízes e inferiores a 360 e 160 mg kg-1 nas folhas e colmos, respectivamente, evidenciando que o Al foi acúmulo nas raízes das plantas. De modo geral, as concentrações de macro e micronutrientes variaram com os tratamentos e cultivares, porém sem valores altos e baixos extremos. Concluiu-se que a cultivar IACSP95-5000 tem maior potencial de produção em resposta à aplicação de calcário e que a saturação de alumínio de 29% não apresenta efeito negativo sobre a produção de matéria seca, exceto da cultivar IACSP95-5000, e estado nutricional das cultivares de cana-de-açúcar / The agricultural field for the cultivation of sugarcane are concentrated in areas of Cerrado, which are acidic soil with high aluminum saturation and low base saturation. For the correction of these characteristics, the use of correctives and fertilizers are needed. Although in acid soils the aluminum toxicity is one of the most serious limitations to the plant growth, there is a lack of studies on the effects of aluminum on sugarcane crop. Based on this, the object of this work was to evaluate the effect of application of limestone or gypsum on the nutritional status of four cultivars of sugarcane, with different nutritional requirement, at the tillering stage of crop. A pot experiment was developed at greenhouse condition. Pots containing 4 kg of a soil, with 29% of aluminum saturation, as substrate were treated with: 1) limestone, 2) gypsum, and 3) control without lime and gypsum application. The IACSP95-5000, IACSP94-2094, SP80-3280, and IAC95-3028 cultivars were tested. After the addition of the treatments, the soil was incubated for 45 days. For plant materials, mini stem cuttings of cultivars were germinated, grown by 90 days and transplanted to pots, for the respective treatments. The plants were fertilized with macro and micronutrients and cultivated along 60 days. The treatments were characterized with regard to chemical attributes for fertility assessment, both after soil incubation and after collecting plants. In plants, chlorophyll, flavonoids, nitrogen balance index (NBI), aluminum and nutrient concentrations, and production of total, leaf, stem and root dry matter were evaluated. While the gypsum treatment did not differ from the control, the limestone treatment was effective for the correction of soil reaction, with increasing the pH value and base saturation, and lowering the aluminum saturation and total acidity, besides increasing the levels of Ca and Mg. In plants, for all cultivars, the contents of chlorophyll, flavonoids and NBI were improved by limestone treatment, comparing to control and gypsum. Generally, the IACSP95-5000 cultivar had higher total plant parts dry matter production, following by IACSP35-3028 with an intermediate production, and by IACSP94-2094 and SP80-3280 with lower production. For treatments, there was no effect of limestone and gypsum on the production of leaf dry matter, however limestone increased the dry matter production of stem and root by IACSP95-5000. Regardless of treatment, the cultivars showed aluminum concentration greater than 5000 mg kg-1 in the roots, and less than 360 and 160 mg kg-1, respectively, in leaves and stems, showing that the Al was accumulated in the roots of plants. In General, the concentrations of macro and micronutrients varied with the treatments and cultivars, however without extreme high and low values. It was concluded that the cultivar IACSP95-5000 has greater potential production in response to the limestone application, and that the aluminum saturation of 29% poses no negative effect on dry matter production, except of the cultivar IACSP95-5000, and on nutritional status of the studied sugarcane cultivars

A 1-D tidal, salinity and water quality model that analyzes the impacts of freshwater diversions with median and high flow on the water level, salinity and nutrient concentration of the Barataria Basin over a 2 period is presented here. The model predicts that the salinity of Lower Barataria decreases with the introduction of freshwater diversions. The model also predicts that nutrient concentration increases in Barataria Basin and decreases in Northern Gulf of Mexico with the introduction of diversions. The model shows the impact of freshwater diversions on water level except in the neighborhood of the diversion sites are small.

Snap bean (Phaseolus vulgaris L.) production by large scale commercial producers in Ethiopia is under intensive production and relies on high rates of nitrogen (N) fertilizer and irrigation during the dry season. Despite increasing interest to produce this crop, small scale farmers cannot afford the high cost of N fertilizer. Field and greenhouse experiments were conducted to test snap bean production under a low input production system better suited to small scale resource limited farmers. Field experiments were conducted in 2011 and 2012 under rain fed conditions, and in 2012 under irrigation, at three locations (Debre Zeit, Hawassa, Ziway) representing different climate zones in Ethiopia. This experiment used three N treatments: 0 and 100 kg N ha-1, and inoculation with Rhizobium etli [HB 429], and eight cultivars: Andante, Boston Contender Blue, Lomami, Melkassa 1, Melkassa 3, Paulista and Volta. The general objective of the field experiment was to determine the potential of snap bean production under a low input production system using rhizobium inoculation as the nitrogen source, and use rain fed conditions. Results obtained indicated that rhizobial inoculation and applied inorganic N increased on average the marketable pod yield of snap bean under rain fed conditions by 18 % and 43%, respectively. Nodulation and subsequent N2 fixation was not effective in improving yield or other traits of snap bean pod under irrigation, although applied N increased marketable yield by 33%. Melkassa 1 was the most suitable cultivar for a reduced input production system due to its successful nodulation characteristics, greatest N2 fixation levels and consistently good performance across locations under rain fed conditions. Commercial cultivars possessed the best pod quality characteristics and they yielded better under irrigation. Cultivars interacted with locations to affect pod traits including total soluble solids and concentrations of protein, calcium, and potassium under rain fed conditions. Snap bean cultivrs produced at Debre Zeit and Hawassa were similar in marketable yield and several other traits particularly under rain fed conditions. Zinc (Zn) concentration in pods was greatest at Hawassa both under rain fed and irrigated conditions. Conditions at Debre Zeit were the most conducive for supporting biological N2 fixation for snap bean production. The eight cultivars were also used for a greenhouse study that was evaluated treatments of drought stress of 50% field capacity (50% FC) during the vegetative (V4.4), flowering (R6) and pod formation (R7) developmental stages. Our result showed that drought stresses during reproductive stages (R6 and R7) were the most sensitive stages in deteriorating the quality of snap bean pods. Drought stress increased protein, phosphorus and Zn concentrations but it reduced iron concentration in snap bean pods. All cultivars had a similar response to drought stress. A second greenhouse experiment was conducted to test foliar application of growth regulators: the control, 10-5 M and 10-4 M concentrations of each of abscisic acid (ABA), kinetin and salicylic acid (SA); and two concentrations of yeast extract (4 g l-1 and 8 g l-1), under drought (50% FC) stressed and unstressed conditions. Foliar application of SA on snap bean under greenhouse conditions reduced the impact of drought stress, particularly the pod quality parameters: marketable yield, pod curving, texture and appearance of snap bean pods. However, application of ABA, kinetin and SA reduced pod quality of snap bean under unstressed conditions. In conclusion, pod yield improvement could be achieved by a N2 fixation system under rain fed conditions, which is more sustainable than N fertilizer inputs. Pod quality was also adequate for commercial export production. Rhizobium inoculant can therefore be used as an alternative N source, particularly under low input production system for resource-limited small-scale snap bean producers.

<p dir="ltr">Routine testing of nutrient concentrations via plant tissue is an important component of in-season fertilizer management in maize (<i>Zea</i> <i>mays </i>L.) cropping systems. Accuracy of results are critical for nitrogen (N), phosphorous (P), potassium (K), and sulfur (S) management, yet there is little scientific guidance on which leaf to sample during mid- to late-vegetative growth stages. Additionally, the whole-plant status of each macro-nutrient may be best represented by a different leaf position due to mobility differences among nutrients. Mobility of each nutrient and allocation within the plant may also be influenced by environmental factors, management strategies, and genotype selection. Field experiments were conducted in West Lafayette and Windfall, Indiana in 2021 and 2022. The objectives were to (1) evaluate N, P, K, and S concentrations of specific leaf positions and whole plants in response to N fertilizer rate (NR), planting density (PD), and genotype (G) treatments at multiple growth stages, and (2) determine the ability of various leaf positions to predict whole-plant concentrations of N, P, K, and S across multiple NR, PD, and G environments. The West Lafayette study compared three NR treatments applied as urea-ammonium nitrate (UAN, 28-0-0) at the V5 growth stage and included (1) Control, no N applied, (2) 151 kg N ha^-1, and (3) 241 kg N ha^-1. The Windfall study compared two side-dress UAN rates of (1) Control, no N applied, and (2) 224 kg N ha^-1 at two planting densities (sub-plot) of 49,400 plants ha^-1and 89,000 plants ha^-1 with 4 Pioneer^® genotypes (sub-sub-plot) including two historical double-cross hybrids and two modern single-crosses. Tissue sampling included the top-collared leaf and whole-plant at V8, the 8^th leaf, top-collared leaf, and whole-plant at V12, and the 8^th leaf, 12^th leaf, ear-leaf, top-collared leaf and whole-plant at R1. Tissue N concentrations were consistently responsive to NR and PD treatments at all stages, but bottom leaves better reflected NR changes. As a mobile nutrient, N concentrations were highest in the uppermost leaf positions by R1 (ear-leaf and top-leaf), yet regressions between individual leaf and whole-plant N% were highest in the lower leaf positions (8^th and 12^th leaf positions). This suggested that the more likely a specific leaf was to exhibit nutrient deficiency symptoms, the better it would be at predicting whole-plant concentrations of that nutrient. Regressions between individual-leaf and whole-plant N% (modern genotypes only) increased from V8 to R1 and regressions were best with the 12^th leaf position at both V12 and R1. Tissue S concentration responses to NR increased at later growth stages, and top-leaf S was a stronger reflection of whole-plant S than the 8^th leaf. Despite S concentration differences among leaf positions at R1, the strength of regressions between each leaf position and whole-plant S were similar. There was no optimal leaf position to represent whole-plant S. While leaf N and S concentrations were above whole-plant concentrations, leaf P and K concentrations exhibited the opposite dynamic. There was little leaf P response to experimental treatment factors, and although regressions for leaf P versus whole-plant P concentrations were far weaker than for N, S or K, the 8^th leaf position was preferred at V12 and R1 (R² of just 0.27 and 0.36, respectively). Potassium concentration response to NR was weak. However, leaf K% and whole-plant K% were highly related via regression, irrespective of NR, at all three stages. Prediction of whole-plant K was strongest with the 8^th leaf at V12 and the 12^th leaf at R1. In summary, optimum leaf sampling position was shown to vary with individual macronutrients and growth stages in maize. Although more research is essential, these preliminary results indicate that traditional sampling methods involving selection of the top fully-expanded leaf from V8 to silking, and the ear-leaf during post-silking stages, may not be the most reliable indicators of whole-plant nutrient status.</p>

ABSTRACT It may be of no surprise that water quality data is right-skewed, but what appears to be overlooked by some is that the arithmetic mean and standard deviation most often fail as measures of central tendency in skewed data. When using the arithmetic mean and arithmetic standard deviation with nutrient data, one standard deviation about the arithmetic mean can capture nearly all of the data and extend into negative values. Representing nutrient data this way can be misleading to viewers who are using the statistics, and making assumptions, to understand the characteristics of those waters. Through an in-depth statistical analysis of Florida's nitrogen and phosphorus data, I have found the geometric mean and multiplicative standard deviation capture a better representation of the central region of skewed data. Including the geometric mean and multiplicative standard deviation in the descriptive statistics of nutrient data is relatively simple with today's tools and helps to better describe the data. Adding these statistics can contribute to more effective understanding of nutrient concentrations, better application of data, and the development of better data-derived policy. While the suggestions of this paper are by no means original, it is with added evidence provided by the study of the skewness, distributions, and central regions of 53 nutrient data sets that I intend to help reiterate the argument that a few additional descriptive statistics can greatly empower the communication of data, and because of the ease with which they can now be calculated, there is no excuse to ignore them.

Hedgerows of the fodder tree legume Leucaena leucocephala (Lam.) de Wit ssp. glabrata (Rose Zárate) (leucaena) planted with companion grass (leucaena-grass pasture) form a productive, profitable and sustainable tropical pasture in northern Australia. Leucaena is renowned for its longevity (>30 years) and productivity under regular grazing, and this is a key factor in its profitability. To-date graziers and researchers have not been concerned about the sustainability of commercial leucaena-grass pastures, which are rarely fertilized. However, nutrient depletion could be expected after many years of nutrient removal under heavy grazing without replenishment, even on soils of moderate initial fertility. This study investigated the long-term productivity of leucaena-grass pastures in relation to nutrient depletion in Queensland. Experimental trials were conducted at 3 research stations and 6 commercial cattle properties. Prior to conducting field trials, a postal survey of leucaena growers ascertained perceived changes in leucaena, grass and livestock productivity over time. Physical and management factors influencing long-term pasture productivity were also explored. Graziers reported that leucaena productivity had declined in 58% of aging pastures. Lower livestock productivity was associated with declining leucaena growth, even though grass growth remained vigorous. Leucaena growth decline was more frequent on soil types of marginal initial fertility. Maintenance fertilizer was not applied to most (98%) leucaena pastures surveyed despite significant amounts of nutrient removal, particularly phosphorus (P) and sulphur (S), occurring over prolonged periods of moderate to high grazing pressure. It was predicted that under current management practices large areas of commercial leucaena pasture will be affected by soil nutrient depletion over the next 10 years. The effect of age of leucaena plants on pasture productivity was investigated in pastures aged from 8 to 38 years. Leucaena growth, expressed as rainfall use efficiency (RUE), declined with age (from 4.0 to 1.9 kg total dry matter (DM)/ha/mm), as did leaf nitrogen (N), P and S concentrations. Leucaena productivity decline was attributed to P and S deficiency restricting growth and symbiotic dinitrogen (N2) fixation. Composition of interrow grass changed from native grass dominance before leucaena establishment to green panic (Panicum maximum var. trichoglume) dominance in the aging leucaena pastures, particularly adjacent to leucaena hedgerows. This was attributed to increased soil Navailability. Leucaena and grass roots were concentrated in the topsoil; however, leucaena roots did extend beyond 1 m depth while grass roots did not. Changes in topsoil organic carbon (OC) and total nitrogen (TN) resulting from the planting of leucaena hedgerows into native grass pastures and previously cropped soils were studied. Topsoil OC and TN contents increased significantly under leucaena pasture (OC from 81-290 kg/ha/year and TN from 12-24 kg/ha/yr). Since TN and OC showed similar trends, there was no significant effect on carbon:N ratios. Leucaena contributed to soil OC both directly via plant part decomposition, and indirectly, via enhanced grass growth in the inter-row. Lower topsoil OC accumulation rates (81 kg/ha/yr) were observed in the older leucaena-grass pastures related to the decline in yield and vigour of leucaena in these aging pastures. The amount of carbon dioxide equivalent (CO2-e) accumulated in soil OC in productive leucaena-grass pasture was estimated to be higher than the amount of CO2-e emitted in methane from beef production from these pastures, thus positively impacting on their greenhouse gas balance. Leucaena responses to P and/or S applications were evaluated in a 30 year-old leucaenagrass pasture. Leucaena RUE and symbiotic N2 fixation were restricted by S deficiency. Sulfur concentration in leaf tissue and high N:S ratio were useful indicators of S deficiency. Although leucaena growth and its nutritional status were little affected by P application, symbiotic N2 fixation did respond significantly to P application. Leucaena and grass responses to fertiliser applications were further evaluated at a variety of soil types and environments on 8 sites in Queensland. Increased leucaena RUE (from 3.1 to 4.6 kg total DM/ha/mm) and enhanced nutritional status at most sites showed that leucaena plants were restricted by P and/or S deficiency. The major factors contributing to the P and S deficiencies were: a) inherent low soil P and/or S fertility, b) nutrient removal by cropping and grazing, c) shallow soils, d) acid soils, and e) grass competition for available water and nutrients. Inter-row cultivation (with or without fertiliser) had little effect on leucaena growth but significantly increased grass RUE (from 4.7 to 7.0 kg total DM/ha/mm) at some sites probably due to enhanced mineralization of N. Leaf P and S concentrations were not reliable indicators of deficiencies of these nutrients, possibly due to inadequate leaf sampling conditions. The effects of ambient temperature, water stress and phenological development of plant on nutrient concentrations in leucaena leaf was investigated to determine whether leaf tissueanalysis can reliably predict nutrient deficiencies. The youngest fully expanded leaf (YFEL) was established as the most appropriate leaf tissue for predicting nutritional status of leucaena plants since the YFEL: (a) was an easily identifiable tissue in which nutrient shifts were at a minimum; (b) provided information for readily mobile (N, P and potassium) and variably mobile (S, copper and zinc) nutrients, thus simplifying leaf collection; and (c) facilitated comparison of data from leaves of similar physiological age in different growing conditions and sites. Nutrient concentrations in YFEL were significantly influenced by water stress and phenological stage of plant development (particularly flowering and pod filling) through the mechanism of rate of leaf appearance. Chronological age of the YFEL, an indicator of leaf appearance, varied from 12 to >70 days depending upon plant phenological stage, being >140 days under prolonged water stress. It was found that nutrient concentrations in leucaena YFEL can only be interpreted against critical concentrations if plants are actively growing (October-April) in a vegetative stage and YFEL are <20 days old. This will occur if there is no water stress for ≥28 days prior to sampling. A close correlation existed between chronological age of YFEL and leaf calcium (Ca) concentration. Calcium concentration could be used to assess the age of YFEL and thereby determine the suitability of tissue samples for nutrient analysis and interpretation. Leaves with Ca concentrations >0.7% DM should be discarded as they are likely to be too old (>20 days). The research program has identified that leucaena established on non-alluvial soils need to be provided with regular maintenance P and S fertiliser to promote symbiotic N2 fixation and to maintain high RUE. At present, many leucaena pastures are likely to be suffering undiagnosed nutrient deficiencies that will be limiting pasture and animal productivity and enterprise profitability. Youngest fully expanded leaf analysis can be used as a predictive tool to diagnose nutrient deficiencies provided the recommended protocol is followed. Further investigation is required to: a) assess the duration of responses to applied fertiliser to determine frequency of application; b) investigate the rate of maintenance fertiliser P and S that has to be applied to maintain leucaena symbiotic N2 fixation and RUE at a desired level to benefit both forage quality and quantity, and soil fertility; c) study methods of fertiliser placement for adequate and timely supply of nutrients, particularly P, to leucaena roots; and d) confirm the use of Ca concentration in YFEL as a predictor of optimum leaf age for the range of soils and areas where leucaena is grown.