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Laird, R.J.

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Laird
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R.J.
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Laird, R.J.

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  • Treatment design for fertilizer use experimentation
    (CIMMYT, 1973) Cady, F.B.; Laird, R.J.
    Ideally the experimenter would like to use treatment design to minimize both variance and bias problems in estimating yield from fertilizer application. Selecting a treatment design for variance considerations will not give a minimum bias design. Since different criteria of optimality lead to different designs, the most appropriate criterion under a given set of circumstances will be determined by the specific use that is made of the data generated by the design, e.g., in fertilizer use studies the slope of the estimated response surface near the economic optimal could be most important. For the quadratic polynomial estimating function and a square root true function in two variables, treatment designs are compared empirically using several variance criteria in addition to a volume concept of bias. In general, bias is decreased by restricting the treatment combinations to an area of the factor space not including the boundaries. Increased variance of various estimated parameters may be controlled through replication of the relatively small treatment designs needed for bias considerations.
    Publication
  • Combining data from fertilizer experiments into a function useful for estimating specific fertilizer recommendations
    (CIMMYT, 1969) Laird, R.J.; Ruiz, B.A.; Rodriguez, J.H.; Cady, F.B.
    The decision of greatest economic importance that farmers have to make in using fertilizers is the selection of the fertilizer treatment to employ. T f the treatment selected includes an element that is not needed or a rate of an element higher than the economic optimum, the farmer will not realize the maximum returns from his investment in fertilizers and may even suffer a loss. On the other hand, if he applies less than the optimal amount of fertilizers, he will only be partially exploiting this source of added farm income. The determination of optimal rates of fertilization is one of the most important functions of adaptive research. It is especially difficult to arrive at fertilizer recommendations for specific producing conditions as crop response to fertilization depends on the nature of the crop itself, the characteristics of the soil and climate at the location where it is grown, and the management practices employed in growing the crop. A significant change in any one of a large number of crop, soil, climatic, and management factors can greatly modify the reaction of the crop to fertilization. The optimal rate of nitrogen fertilization, for example, may depend just as much ·on the rainfall or the moisture retention characteristics of the soil as on the nature of the crop or the level of available soil nitrogen. Ideally, two types of information are needed for making specific fertilizer recommendations: (a) The general yield equation for the crop with yield expressed as a function of applied fertilizer variables and the productivity factors, and ( b) The levels of the productivity factors for the specific conditions for which a fertilizer recommendation is sought. Unfortunately there are no well defined procedures to follow in generating a general yield equation and in characterizing the productivity factors. Consequently, the results obtained in field experiments are usually averaged over broad geographical areas to produce general fertilizer recommendations. The present study was carried out with two principal objectives in mind: (a) To produce a general yield equation useful in estimating nitrogen fertilizer needs of unirrigated corn, for specific producing conditions in a region with highly variable rainfall, and ( b) To acquire a better understanding of the problems involved in measuring the productivity factors and in employing the multiple linear regression model for calculating a general yield function. The experimental part of this study was conducted during the period 1962-1965. Simple fertilizer trials were carried out with unirrigated corn in farmer's fields in the Bajio area of Central Mexico. The results obtained in the first two years of this study have already been published, so only the results obtained in 1964 and 1965 will be reported here.
    Publication
  • Field technique for fertilizer experiments
    (CIMMYT, 1968) Laird, R.J.
    As farmers make the transition from traditional to modern agriculture their total operation changes. One of the important decisions they have to make during this period is which fertilizer to apply and how much. An important function of adaptive research is to assist farmers in making this kind of decision so that they will realize maximum returns from a given investment. Useful data for determining optimal fertilization practice are derived primarily from field experiments. Data obtained in these experiments are also used for calibrating soil and plant testing procedures, which, subsequently, are useful in making recommendations on fertilizer use for specific farming conditions. The modern approach to fertilizer use experimentation assumes that variability in fertilizer response among sites in an area of study arises mainly from measurable differences in the soil, plant, climate, and management factors. Experiments are located to sample the major differences in soil and climate; plant and management factors are controlled at near-optimal levels; observations are made during the course of the experiments to characterize the productivity factors; and the results are expressed in the form of a general yield equation. Through field experiments conducted in this manner it is possible to determine a quantitative relationship among crop yield, applied fertilizers and the productivity conditions for a given region. This general relationship serves as a basis for making fertilizer recommendations for specific farming conditions. However, certain principles must be carefully observed in locating the experiments, selecting the treatment design, defining the rates of fertilization, conducting the experiments, and analyzing and interpreting the results. This manual treats in detail only one part of the general methodology, the technique of carrying out the field experiments. Fertilizer trials conducted in farmer's field are frequently lost or fail to produce useful information due to an oversight or failure to perform some function properly at the correct time. Careful attention to the principles and details described here should greatly reduce the frequency of such loss and increase the usefulness of data obtained in the harvested trials. This manual has been prepared as a guide for agronomists who are initiating adaptive research on fertilizer needs of crops. A study of the fertilization of unirrigated maize in an important agricultural region of Central Mexico is described. This manner of presentation permits a detailed examination of the several activities involved in fertilizer use studies with maize and, in addition, shows how these activities are organized chronologically. The details described here will vary somewhat for plantings of maize under other conditions and may be greatly different for other crops. However, the principles apply equally well to maize and to other crops.
    Publication
  • Tecnicas de campo para experimentos con fertilizantes
    (CIMMYT, 1968) Martínez Valdés, G.; Laird, R.J.
    La tecnificación de la agricultura significa para los agricultores un cambio total en sus prácticas de manejo. Una de las decisiones importantes que deben tomar al modernizar su explotación agrícola es cuál y cuánto fertilizante hay que aplicar. Una función importante de la investigación aplicada es ayudar a los agricultores a tomar este tipo de decisión de manera que obtengan la máxima utilidad de una inversión dada. Los datos útiles en la determinación de las prácticas óptimas de fertilización se derivan principalmente de experimentos de campo. Los datos que se obtienen de estos experimentos también se usan para calibrar procedimientos analíticos de suelo y planta, los cuales subsecuentemente, son útiles al hacer recomendaciones de fertilizantes para condiciones específicas de producción. El enfoque moderno en la experimentación sobre uso de fertilizantes supone que la variabilidad en la respuesta a los fertilizantes entre sitios de un área de estudio se origina principalmente de diferencias mensurables en los factores suelo, planta, clima y manejo. Los experimentos se localizan para muestrear las diferencias principales en suelo y clima; los factores de planta y de manejo se controlan a niveles casi-óptimos; durante el transcurso de los experimentos se hace observaciones para caracterizar los factores de productividad, y los resultados se expresan en la forma de una ecuación general de rendimiento. Mediante los experimentos de campo llevados a cabo de esta manera, es posible determinar una relación cuantitativa entre rendimiento del cultivo, fertilizantes aplicados y condiciones de productividad para una región dada. Esta relación general puede servir como base para hacer recomendaciones de fertilizantes para condiciones específicas de cultivo. Sin embargo, deben observarse cuidadosamente ciertos principios al localizar los experimentos, seleccionar el diseño de tratamientos, definir las dosis de fertilización, llevar a cabo los experimentos y analizar e interpretar los resultados. Este manual trata en detalle solamente una parte de la metodología general: las técnicas empleadas en el desarrollo de los experimentos de campo. Los ensayos de fertilizantes llevados a cabo en campos de agricultores frecuentemente se pierden o no producen información útil debido a yerros o fallas en el desempeño apropiado de alguna función en el tiempo correcto. La atención cuidadosa a los principios y detalles descritos aquí debiera reducir considerablemente la frecuencia de tales pérdidas e incrementar la utilidad de los datos obtenidos en los ensayos cosechados. Este manual se ha preparado como una guía para los agrónomos que están iniciando investigación aplicada sobre necesidades de fertilizantes de cultivos. Se describe aquí un estudio sobre fertilización de maíz de temporal en una importante región agrícola de la zona centra, de México. Esta manera de presentación permite un examen detallado de las varias actividades involucradas en estudios sobre uso de fertilizantes con maíz y, además, muestra cómo estas actividades se organizan cronológicamente. Los detalles aquí descritos variarán algo para siembras de maíz bajo otras condiciones y pueden variar grandemente para otros cultivos. Sin embargo, los principios se aplican igualmente bien para maíz que para otros cultivos.
    Publication