Fertilidad del suelo y calidad nutricional de estacas de yuca (manihot esculenta crantz)

Se estudió el cambio en el contenido nutricional de los tallos de yuca ocasionado por diferentes niveles de fertilización al suelo y el efecto de las estacas obtenidas de esos tallos sobre el cultivo subsiguiente. Los 9 niveles nutricionales del suelo incidieron en la altura y vigor de las plantas madres. Tanto la concentración como el contenido de N-P-K variaron notablemente según el nivel de fertilización utilizado, siendo más bajos entre más baja fuera la cantidad de cada nutrimento aplicada. La germinación más baja ocurrió con potasio o niveles altos de N y de P. La siembra del material en un suelo con o sin fertilizante no incidió en su capacidad de germinación debido al efecto de las reservas nutricionales de la estaca. La mayor producción de follaje y de tallos aptos para usar como material de siembra, el mayor rendimiento de raíces totales y la mayor producción de raíces de tamaño comercial se obtuvieron utilizando estacas provenientes de las parcelas a las cuales se aplicaron los niveles más altos de N-P-K.A study was conducted on the changes in nutritional content of cassava stems as a result of different soil fertilization levels, and on the effect of the stakes obtained from these stems on the subsequent crop. Results showed that the mother plants had different height and vigor depending on the 9 different nutritional levels of fertilizer application to the soils where they were grown. Stems of each of the 9 treatments produced stakes with different weights. Both the concentration ami the N-P-K content varied considerably depending on the fertilization treatment. These two parameters were lower when the amount of nutrient applied to the soil was lower. Germination percentage was strongly influenced by the level of K application as well as by its balance with N and P. The lowest germination percentage was registered by the treatment that received no K, but which had received a high level of N and P, which caused an disequilibrium in absorption of the elements. Germination potential was not affected by having planted the stakes in soils with or without fertilizer application, since what is important for this process was the amount of nutritional reserves that the stakes already brought with them, Stakes coming from plots with the highest level of N-PK application became plants with greater production of foliage and stems that were apt to be used as vegetative seed. These stakes also resulted in plants with greater total rood yield and greater production of commercial size roots

Respuesta fotosintética de la yuca (manihot esculenta crantz) en dos ambientes

El trabajo de campo se llevó a cabo en dos localidades de la costa Atlántica Colombiana, Riohacha en la Guajira, considerada como zona semi-arida y Santo Tomás Atlántico, como zona sub-húmeda. La respuesta a la humedad relativa se evaluó en diez cultivares, entre las 8 y las 13 horas empleando un equipo de fotosíntesis portátil de sistema abierto; en ensayos diseñados en bloques al azar con cuatro repeticiones; las lecturas se realizaron en la primera hoja expandida, sana y bien formada de parte superior de dos plantas de cada parcela. Se encontraron diferencias significativas entre clones para cada localidad en las variables de fotosíntesis, conductancia y transpiración. La prueba de T mostró diferencias altamente significativas entre las localidades para todas las variables. En la condición sub-húmeda se presentó la que mayor tasa de fotosíntesis, lo cual indica que la yuca produce mejor en condiciones de alta humedad relativa en el aire y que responde a esta en forma independiente a la humedad del suelo. Las hojas de yuca se saturan a intensidades de más o menos de 1000 µmol m-1 s-1 valor relativamente alto, si se tiene en cuenta el déficit de agua en el suelo al que estaban sometidas las plantas en el momento de las evaluaciones. Esto muestra el alto potencial que tienen las hojas de yuca a la fijación de CO2 aun en condiciones de estrés hídrico.Field work was carried out two locations of the Atlantic Coast of Colombia, namely Riohacha, in the Guajira Department, and Santo Tomás, in the Atlantic Department. The former is a semi-arid zone and the latter a sub-humid zone. Ten Cassava cultivars were evaluated for their photosynthetic response to relative humidity by means of an open system photosynthesis recorder. Evaluations were done from 8:00 a.m. through 1:00 p.m. in plots of randomized block trials with four replications. In each plot, two plants were selected for readings, which were performed on a healthy and well formed leaf among the first expended leaves in the upper part of the plant. For each location, data were significant between cassava clones for the photosynthesis, conductance and transpiration variables. The T-test was highly significant between locations, and for all variables tested, Plants in the sub-humid zone showed the highest photosynthetic rate; this indicates that cassava production is higher in areas where air relative humidity is high, independent of the plant response to soil water content. Leaves saturate at light intensities of around 1000 µmolm-1 s1- . Considering the soil deficit that affected plants at the time of the evaluation, this relatively high value indicates that CO2 fixation rate in cassava leaves is high even under water stress conditions

Utility of basic research in plant/crop physiology in relation to crop improvement : A review and a personal account

Agricultural research and development plays an essential role in a nation's economic development, providing for food security for an ever-increasing population. In developed countries, the gap between potential and actual yield is largely closed because of a combination of advanced technologies, high-yielding new varieties and the application of agrochemicals in highly mechanized production systems. In most of these countries, agricultural production exceeds national demand, resulting in excess products for export. In many of the developing countries, however, agricultural productivity is still far below what it should be because of multiple technical and socio-economic constraints. Food deficits are the norm in poor and middle-income countries, requiring expensive food imports. To partially alleviate this situation, agricultural research must be strengthened. As branches of basic sciences, plant and crop physiology have often been criticized for being non-effective in translating their findings into improving crop productivity, which would enhance agricultural progress. This paper addresses this issue by presenting an assessment of past achievements of physiological research and their impacts on crop improvement and food production. Shortcomings and limitations of isolated, non-relevant research are discussed, along with scientist views on how effective physiological research should be conducted and integrated within breeding-based multidisciplinary research teams. Examples of successful research in crop physiology and their contributions towards increasing crop productivity are given. All this points to the need for steadfast funding of basic research by public and private sectors of developed countries. = A pesquisa e o desenvolvimento agrícola têm função essencial no desenvolvimento econômico das nações, provendo segurança alimentar para uma população em constante crescimento demográfico. Em países desenvolvidos, as lacunas entre a produção potencial e a produção real são sobremodo estreitas, devido a uma combinação de tecnologias avançadas, novas variedades altamente produtivas e aplicação de agroquímicos em sistemas de produção altamente mecanizados. Na maioria daqueles países, a produção agrícola supera a demanda nacional, resultando em excedentes para a exportação. Em muitos países em desenvolvimento, entretanto, a produtividade agrícola está ainda muito abaixo de seu potencial devido a limitações técnicas e sócio-econômicas. Déficit alimentar é a norma em países pobres e subdesenvolvidos, os quais requerem vultosas importações de alimentos. Para aliviar parcialmente essa situação, pesquisas de cunho agrícola devem ser reforçadas. Como ramos das ciências básicas, a fisiologia vegetal e a fisiologia da produção têm sido freqüentemente criticadas por não traduzirem seus resultados de pesquisa em melhoria da produtividade. Este artigo é focado nesse tema, apresentando uma avaliação das realizações pretéritas da pesquisa fisiológica e de seus impactos sobre o melhoramento das culturas e sobre a produção de alimentos. Discutem-se deficiências e limitações de pesquisas isoladas e de pouca relevância, juntamente com opiniões do cientista sobre como pesquisas efetivas na área da fisiologia devem ser conduzidas e integradas dentro de equipes de pesquisa multidisciplinares associadas ao melhoramento vegetal. Exemplos de pesquisas de sucesso na fisiologia da produção e suas contribuições para aumentar a produtividade agrícola são apresentados. Todos esses aspectos apontam para a necessidade de pronto financiamento da pesquisa básica por setores públicos e privados de países desenvolvidos

Physiological characteristics of cassava tolerance to prolonged drought in the tropics : Implications for breeding cultivars adapted to seasonally dry and semiarid environments

The paper summarizes research conducted at International Center for Tropical Agriculture (CIAT) on responses of cassava to extended water shortages in the field aided by modern gas-exchange and water-relation techniques as well as biochemical assays. The aim of the research was to coordinate basic and applied aspects of crop physiology into a breeding strategy with a multidisciplinary approach. Several physiological characteristics/traits and mechanisms underpinning tolerance of cassava to drought were elucidated using a large number of genotypes from the CIAT core germplasm collection grown in various locations representing ecozones where cassava is cultivated. Most notable among these characteristics are the high photosynthetic capacity of cassava leaves in favorable environments and the maintenance of reasonable rates throughout prolonged water deficits, a crucial characteristic for high and sustainable productivity. Cassava possess a tight stomatal control over leaf gas exchange that reduces water losses when plants are subjected to soil water deficits as well as to high atmospheric evaporative demands, thus protecting leaves from severe dehydration. During prolonged water deficits, cassava reduces its canopy by shedding older leaves and forming smaller new leaves leading to less light interception, another adaptive trait to drought. Though root yield is reduced (but much less than the reduction in top growth) under water stress, the crop can recover when water becomes available by rapidly forming new canopy leaves with much higher photosynthetic rates compared to unstressed crops, thus compensating for yield losses with final yields approaching those in well-watered crops. Cassava can extract slowly water from deep soils, a characteristic of paramount importance in seasonally dry and semiarid environments where deeply stored water needs to be tapped. Screening large accessions under seasonally dry and semiarid environments showed that yield is significantly correlated with upper canopy leaf photosynthetic rates, and the association was attributed mainly to nonstomatal (anatomical/biochemical) factors. Parental materials with both high yields and photosynthetic rates were identified for incorporation into breeding and selection programs for cultivars adapted to prolonged drought coupled with high temperatures and dry air, conditions that might be further aggravated by global climate changes in tropical regions

Sink-source relations in cassava: Effects of reciprocal grafting on yield and leaf photosynthesis

Two contrasting clones of cassava (Manihot esculenta) were reciprocally grafted to test the hypothesis that the yield of cassava is limited by the number of storage roots. Effects of the root sink on leaf gas exchange were also tested under field conditions using a portable infra-red gas analyzer. Storage root number and root yield were affected by stock size and root yield was associated with the number of storage roots. The harvest index and sink-source ratio (root numberz/leaf area index) were correlated with root number. A feedback effect of root number on single-leaf photosynthesis was observed in one clone. It is concluded that the number of storage roots may be used as an indicator of sink strength

Cassava varietal response to fertilization: Growth dynamics and implications for cropping sustainability

Four contrasting varieties of cassava (Manihot esculenta Crantz) were grown for ten months over two consecutive seasons in hillside Colombia with or without nitrogen, phosphorus and potassium fertilization. Sequential harvests were every two months. The two varieties well adapted to acid soils (CM 489-1 and CM 523-7) had higher yields and exhibited the strongest response to fertilization, highest solar radiation use efficiency, earlier canopy ground cover and higher leaf litter accumulation. The export of potassium, however, was no higher than in the other genotypes, mainly as a consequence of higher potassium use efficiency in the adapted varieties. Significant amounts of total calcium, magnesium and nitrogen accumulated in the whole plant were recycled in the leaf litter during growth. High-yielding varieties adapted to acid soils did not exacerbate soil fertility problems of cassava crops; rather, they were beneficial. Certain growth parameters could be used to select for varieties with low impact on soil fertility