I. R. McCann

Potato response to split nitrogen timing with varying amounts of excessive irrigation

Irrigation and nitrogen management are two of the most important factors affecting production efficiency and environmental quality in potato cropping systems. Field studies were conducted in 1990 and 1991 to determine the interactive effects of irrigation amount and N timing on potato yield, quality and nitrate leaching potential. Sprinkler irrigation was applied at approximately 1.0, 1.2 or 1.4 times estimated evapotranspiration (ET) to Russet Burbank potatoes grown on a silt loam soil. Following tuber initiation, a total of 132 kg N/ha was applied through the irrigation system to N treatment subplots using either six weekly 22 kg N/ha applications or 3 biweekly 44 kg N/ha applications.Excessive irrigation reduced root zone and petiole NO3-N concentrations during substantial portions of the tuber bulking period. Biweekly 44 kg N/ha applications in 1991 produced higher and more consistent earlyseason root zone NO3-N concentrations in the 1.2 and 1.4 ET plots than did the weekly 22 kg N/ha applications. Late-season tuber dry weight, total plant dry weight and plant N uptake were not affected by irrigation rate or N timing. However, excessive irrigation reduced U.S. No. 1 yield and yield of tubers >284 g in both 1990 and 1991 and reduced total yield in 1990. Biweekly N applications produced higher U.S. No. 1 yields than weekly N applications at all irrigation levels. Excessive irrigation also reduced NO3-N remaining in the top 60 cm of soil at the end of the growing season. These results show that irrigating at optimal rates and applying split N at two week intervals on a silt loam soil can maximize Russet Burbank yield and quality while minimizing NO3-N losses.CompendioEl manejo del riego y del nitrógeno son dos de los factores más importantes que afectan la eficiencia de la productión y la calidad del ambiente en los sistemas de cultivo de papa. Se condujeron estudios de campo en 1990 y 1991 para determinar los efectos de la interacción de la cantidad de agua aplicada y el momento de aplicación del nitrógeno sobre el rendimiento y la calidad de la papa, y el potencial de lixiviación del nitrógeno. Se aplicó riego por aspersión a aproximadamente 1.0, 1.2 o 1.4 veces la evapotranspiración estimada (ET) a papas Russet Burbank sembradas en un suelo franco-limoso. A continuación del inicio de la tuberización, se aplicaron en el sistema de riego 132 kg N/ha a las subparcelas con tratamiento nitrogenado utilizando ya sea seis aplicaciones semanales de 22 kg N/ha o tres bisemanales de 44 kg N/ha.El riego excesivo redujo la zona radicular y las concentraciones de NO3-N de los peciolos durante considerable parte del periodo de crecimiento de los tubérculos. En 1991 las aplicaciones bisemanales de 44 kg N/ha produjeron en la temporada temprana en las parcelas de 1.2 y 1.4 ET una mayor y más consistente zona radicular, y concentraciones de NO3N, en comparación con las parcelas con aplicaciones semanales de 22 kg N/ha. El peso seco de tubérculo, el peso seco total por planta y la absorción de N por la planta al final de la temporada no fueron afectados por la cantidad de agua de riego ni por el momento de aplicación del N. Si embargo, el riego excesivo redujo el rendimiento de tubérculos U.S. No. 1 y de tubérculos > de 284 g tanto en 1990 como en 1991 así como también el rendimiento total en 1990. Las aplicaciones bisemanales de N produjeron rendimientos más altos de tubérculos U.S. No. 1 que las aplicaciones semanales a todos los niveles de riego. El riego excesivo redujo también al final de la temporada de cultivo los NO3-N remanentes en los 60 cm superiores del suelo. Estos resultados muestran que irrigando con volúmenes óptimos de agua y aplicando el N dividido a intervalos de dos semanas se puede maximizar el rendimiento y la calidad de Russet Burbank al mismo tiempo que se minimizan las pérdidas de NO3-N.

Optimal allocation of limited water supplies for Russet Burbank potatoes

Water shortages in many potato-producing regions have increased the demand for information on irrigating potatoes with limited water supplies. Field studies were conducted at Aberdeen, Idaho in 1988 and 1989 to determine the optimal allocation of limited water supplies for Russet Burbank potatoes. Irrigation amounts equal to 60 or 80% of estimated seasonal evapotranspiration (ET) were applied using various patterns of water allocation. Irrigation deficits were either partitioned evenly over the entire tuber bulking period, or were imposed during two of three designated growth stages (early, mid or late bulking) corresponding to the periods from 0 to 3, 3 to 6, and 6 to 9 weeks after tuber initiation, respectively. A well-watered, 100% ET check was included for comparison. Total yield reductions were greater when irrigation deficits were imposed during the early-mid and midlate bulking sequences than when they were imposed evenly over the entire tuber bulking period or during the early-late bulking sequence. Results relating U.S. No. 1 yields to seasonal water allocation patterns were similar to those for total yield. However, U.S. No. 1 yield reductions were proportionately greater. Irrigation deficits imposed during the early-mid bulking sequence resulted in the lowest specific gravities and the highest percentages of dark ends.CompendioLa escasez de agua en muchas de las regiones donde se produce papa ha originado que se incremente la demanda por información sobre la irrigación del cultivo en condiciones de un bajo abastecimiento de agua. En 1988 y 1989 se condujeron estudios en Aberdeen, Idaho, para determinar la distribución óptima de cantidades limitadas de agua para papas Russet Burbank. Al irrigar se aplicaron cantidades iguales al 60 u 80% de la evapotranspiración (ET) estimada para la temporada utilizando varios esquemas de distribución de agua. Los déficits de irrigación iguales a 20 o 40% de la ET estimada fueron distribuidos ya sea uniformemente durante todo el periodo de formación de tubérculos o fueron impuestos durante dos de tres etapas consideradas de crecimiento (producción temprana, media o tardía) correspondientes a periodos de 0 a 3, 3 a 6 y 6 a 9 semanas después de iniciada la tuberización, respectivamente. Con fines de comparación, se incluyó un testigo irrigado al 100% de la ET. Las reducciones en el rendimiento total fueron mayores cuando los déficits de irrigación fueron impuestos durante las secuencias de crecimiento o durante la secuencia temprano-tardía de crecimiento. Los resultados al relacionar los rendimientos en U.S. No. 1 con los esquemas de distribución fueron similares a aquellos para el rendimiento total. Sin embargo, las reducciones en el rendimiento de U.S. No. 1 fueron proporcionalmente mayores. Los déficits de irrigacion impuestos durante la secuencia temprano-media de crecimiento resultaron en las gravedades específicas más bajas y los porcentajes más altos de extremos oscuros.

Computer control system for spatially varied water and chemical application studies with continuous-move irrigation systems

A microcomputer driven open-loop digital control system for implementing spatially variable water and chemical application from center pivot and linear-move irrigation systems is described. The control system is comprised of readily available commercial components and provides an effective means of implementing variable rate water and chemical application in crop production studies for evaluating potential benefits. The control system was implemented on a three-span 100 m linear-move irrigation system and on a 39-ha commercial center pivot irrigation system. Water and chemical application were monitored to document control system performance. The results show that spatially varied water and chemical application was achieved with the same accuracy as that of conventional uniform application. This paper provides details on the control system hardware and software and documents field performance.

Zone-subsoiling effects on potato yield and grade

Soil compaction and erosion are problems in many Pacific Northwestern potato fields. We wanted to determine if zone-subsoiling would reduce these problems and improve potato yields and or grade without adversely impacting other production practices. Studies were conducted in Southern Idaho at six locations over two years on different soils and with different irrigation methods to assess the effects of zone-subsoiling immediately after planting on tuber yield and grade. Reservoir-tillage comparisons were made at three locations where sprinkler water application rates were higher than soil infiltration rates. Russet Burbank was represented by eight location-years and Russet Norkotah by two. Zone-subsoiling consistently improved tuber grade or increased tuber size. The biggest improvement was under furrow irrigation. Zone-subsoiling also tended to increase total yield in eight of ten location-years. Reservoir-tillage improved yield and grade, but zone-subsoiling did not without reservoir-tillage when water application rates were high. At no location did zone-subsoiling significantly decrease tuber grade or yield. Zone-subsoiling had no appreciable effects on hill configuration or seed-piece dislocation. Surface cracking and “water piping” occurred under furrow irrigation but were not significant problems. Results were similar for both cultivars. Additional studies will be needed to successfully incorporate zone-subsoiling into commercial production practicesCompendioLa compactación y erosión del suelo son problemas presentes en muchos de los campos de papa del noroeste del Pacífico. Se quería determinar si una aradura profunda zonal podría reducir estos problemas y mejorar los rendimientos de papa y/o su grado sin impactar negativamente sobre otras prácticas culturales de producción. Se condujeron estudios al Sur de Idaho, en seis localidades, durante dos años, con diferentes suelos y métodos de irrigatión, para determinar los efectos, de una aradura profunda zonal efectuada inmediatamente después de la siembra, sobre el rendimiento en tubérculos y su grado. Se efectuaron comparaciones de acumulación-aradura en tres localidades donde las tasas de aplicación de agua por aspersión eran más altas que las tasas de infiltración en el suelo. Russet Burbank fue considerada durante ocho localidades-años y Russet Norkotah en dos. La aradura profunda zonal mejoró consistentemente el grado de los tubérculos o incremento el tamaño de los mismos. La mejora más notable se efectuó bajo irrigación por surcos. La aradura profunda zonal también tuvo la tendencia a incrementar el rendimiento total, en ocho de las diez localidades-años. La acumulación-aradura mejoró el rendimiento y grado, pero no sucedió lo mismo con la aradura profunda zonal sin acumulación-aradura cuando las tasas de aplicación de agua fueron altas. En ninguna de las localidades la aradura profunda zonal disminuyó significativamente el grado de los tubérculos o el rendimiento. La aradura profunda zonal no tuvo efectos apreciables sobre la configuratión del lomo del surco o sobre la localizatión de las secciones de los tubérculos-semillas. Bajo irrigación por surco se produjeron grietas superficiales y aguda licuefacción (‘water piping’), pero no constituyeron problemas significativos. Los resultados fueron similares para ambos cultivares. Se requieren estudios adicionales para incorporar exitosamente la aradura profunda zonal entre las prácticas de productión comerciales.

VARIABLE RATE WATER AND CHEMICAL APPLICATION FOR CONTINUOUS-MOVE SPRINKLER IRRIGATION SYSTEMS

Agriculture is beginning to address the production and environmental problems of applying inputs to nonuniform fields by developing equipment which enables input rates to be varied. A prototype control system has been developed to enable continuous move irrigation systems, such as center pivots, to spatially vary water and chemical amounts. The control system was tested from 1992 to 1995 at the University of Idaho on a 100 m long three span linear move irrigation system using catch cans to measure application patterns. Variable flow along the lateral was achieved in a stepwise manner using electric solenoid valves and control modules to operate multiple sprinklers with different nozzle sizes. All signals to the control modules were transmitted along a single cable by a microprocessor according to the position of the irrigation system relative to a target application map. The precision of variable water and chemical applications to different areas within the same field was comparable to that of uniform applications over the entire field.

Field Scale Transport of Bromide Under Variable Conditions Observed in a Furrow-irrigated Field

An experiment was conducted during the summer of 1991 to monitor field scale movement of bromide (Br-) under the variable conditions observed in a 0.81-ha furrow-irrigated fallow field. Twenty-one evenly spaced sampling stations were established, each consisting of a soil solution sampler at 0.3-m depth, and a neutron probe access tube to a depth of 2.1 m. A narrow pulse of Br- tracer was applied by injection through a solid-set sprinkler irrigation system and was subsequently transported downwards by 26 mm of sprinkler irrigation. Three furrow irrigation events were conducted at three-week intervals during the 63-day study period. Soil samples were taken at each station in 0.15-m increments to a depth of 2.4 m prior to each irrigation and at the end of the study period. The three furrow-irrigation events moved the solute front to 0.23-, 0.38-, and 1.13-m depth, respectively. Three piston flow models based on Darcy flow, field capacity, and the Transfer Function model (TFM) were used to predict the movement of the solute. The Darcy flow model under-estimated solute movement by 18% to 43% after each irrigation event. The TFM predicted the movement of solute with reasonable accuracy after the first irrigation but overestimated solute movement for subsequent irrigations. The latter was attributed to the need to calibrate the TFM at deeper depths. The field capacity model was more consistent with observed irrigations, and predicted the movement of solute with reasonable accuracy for the first and second irrigation. However, the field capacity model underestimated the final Br- position. It was hypothesized that preferential flow occurred during the third irrigation, since the infiltration rates increased during this irrigation and the final measured position of Br- was significantly greater than predicted by the piston flow models.

Zoned Tillage for Potato Production

Studies in southeastern Idaho evaluated the potential of tillage under the potato row (zoned tillage) to influence tuber yield and grade. Such tillage is estimated to provide significant improvement in control of water erosion. The ‘Russet Burbank’ variety was grown on silt loam soil under sprinkler irrigation. Major variables included 1) depth of tillage; 2) timing of tillage; 3) amount of irrigation; 4) amount and timing of nitrogen applications; and 5) depletion of soil moisture. Zoned tillage with the Tye Paratill was also compared to that of a conventional chisel. Zoned tillage did not generally affect total yield, but sometimes reduced the amount of malformed tubers. Zoned tillage tended to perform better as plant stress conditions became more severe. Late application of zoned tillage can reduce yield due to plant root disturbance. Lower soil bulk density persisted longer after zoned tillage than after conventional chiseling. The most suitable depth of zoned tillage appears to be 38 to 46 cm. Field traction conditions for zoned tillage are not favorable for large drawbar pull which will limit machine width.

Evaluation and interpretation of the crop water stress index for well-watered potatoes

During the 1988, 1989 and 1990 growing seasons, canopy and air temperatures, solar and net radiation, relative humidity and wind speed were measured at 10 minute intervals during daytime hours in a field of wellwatered Russet Burbank potatoes in southeast Idaho. A linear relationship between canopy temperature minus air temperature and vapor pressure deficit (TC-TA = 0.2 -2.0 VPD) was developed for use in the Crop Water Stress Index (CWSI). Values of CWSI for well-watered potatoes were generally in the -0.4 to 0.4 range, and exhibited a diurnal trend of decreasing values towards midday and increasing values during the afternoon. Wind speed appeared to increase the CWSI and may account for some of the observed variability.CompendioDurante las temporadas de 1988, 1989 y 1990 se midieron las temperaturas de la planta y del aire, la radiación solar y neta, la humedad relativa y la velocidad del viento, a intervalos de 10 minutos, durante las horas del día, en un campo de papas Russet Burbank bien regardas, en el sureste de Idaho. Se desarrolló una relaciń lineal entre la temperatura de la planta menos la temperatura del aire y el déficit de presión de vapor (TC -TA = 0.2 -0.2 DPV), para utilizarla en el Indice de Estrés al Agua del Cultivo (IEAC). Los valores del IEAC para las papas bien regadas estuvieron generalmente entre -0.4 y 0.4 y presentaron una tendencia diurna de valores decrecientes hacia el medio día y valores crecientes durante la tarde. Al parecer, la velocidad del viento incrementó el IEAC y puede en parte ser la causa de la variabilidad observada.