Potassium and N fertilization is often required for maximum potato (Solanum tuberosum L.) production. Nitrogen, K, and K-sources (KC1, K2SO4) are known to affect yield and quality of potatoes but N and K interactions as affected by K-source have not been defined. This study evaluated the N*K and K-source interactions on Russet Burbank tuber yields and specific gravity (SG) in two irrigated field experiments. Nitrogen rates of 0, 112, 224 or 336 kg ha' were combined with selected K rates of 0, 112, 224 or 448 kg ha as either KC1 or K2SO4 in an incomplete factorial. A multiple linear regression model was fit to the data and used to predict yield and SG for a complete factorial for each K-source. Both N and K applications increased yields independent of K-source. Nitrogen decreased yields at the 336 kg ha' rate. Potassium increased yields up to 448 kg K ha'. Both K-sources decreased SG a similar amount with N application; without N, KC1 decreased SG but K2SO4 did not. Nitrogen also decreased SG. Petiole NO 3-N and K concentrations were positively related to yields and negatively to specific gravities. The petiole K concentration 100 days after planting should be above 4.5 for highest tuber yields. The N*K*K-source interaction was important for yields at low available N and for SG at adequate N availabilities. This study showed that N or K fertilizers can be applied according to their respective soil test concentration and the crop's requirement, generally without consideration of K-source. CompendioPara una producciOn maxima de papa (Solanum tuberosum L.) se requiere frecuentemente de la fertilizaciOn nitrogenada y potasica. Se sabe que el nitrogeno (N), el potasio (K) y las fuentes de potasio (KCL, K2SO 4) afectan el rendimiento y la calidad de la papa, pero las interacciones del N y el K en relaciOn a la fuente de K no han sido definidas. Este estudio evaluO en dos experimentos de campo bajo irrigaciOn las interacciones de N*K con la fuente de K sobre los rendimientos en tuberculos y la gravedad especifica (GE) de Russet Burbank. Dosis de nitrogeno de 0, 112, 224 o 336 kg ha-1 se combinaron con dosis seleccionadas de K de 0, 112, 224 o 448 kg ha-1 como 'Contribution from USDA-ARS and the Utah Agric. Expt.

Considerable evidence exists that both N and K influence potato (Solanum tuberosum L.) yields and quality. The impact of nutrients on tuber quality parameters under field conditions should be identified so optimum management practices can be utilized. We evaluated the N and K fertilization by Ksources effects on concentrations of nutrients, reducing sugars, sucrose and starch in the stem and apical tuber ends from two irrigated field experiments with the Russet Burbank cultivar. Nitrogen rates of 0, 112, 224 or 336 kg ha-' were combined with selected K rates of 0, 112, 224 or 448 kg ha-' as either KCI or K2SQ4 arranged as an incomplete factorial. A multiple linear regression model was fit to the data and used to predict the response surface for a complete factorial for each K-source. Nitrogen applications increased or decreased reducing sugars in the apical and stem ends, respectively. Potassium decreased reducing sugars in both tuber ends. Sucrose was higher in the apical end than in the stem end but was not appreciably affected by fertilizer treatment. Nitrogen and potassium applications reduced dry matter and starch concentrations in both tuber ends. Potassium had a smaller effect on the apical end when starch was expressed on a dry weight basis, indicating that increased water content was a factor in the K effect. Both N and K concentrations in the tuber ends were negatively related to starch concentrations, but the relationship was different for the apical and stem ends. Tuber Cl concentration indirectly affected starch concentrations in the stem end when KCL was applied. The K fertilization effect on specific gravity depended upon the K concentration in the harvested tuber and was independent of K fertilizer source. These data illustrate the effects of preplant N and K fertilization rates on final tuber quality parameters. Additional studies are needed to further define the effects of nutrient concentrations at different plant growth stages. CompendioExiste considerable evidencia que tanto el N coma el K influencian los rendimientos y calidad de la papa (Solanum tuberosum L. campo, debe ser identificado de modo que pueden utilizarse practicas Optimas de manejo. Se evaluO la fertilizaciOn con N y K por los efectos de las fuentes de K sobre la concentraciem de nutrientes, los aplcares reductores, sucrosa y almidem en los extremos apical y terminal de tuberculos de dos experimentos de campo bajo irrigaciem, con el cultivar Russet Burbank. Se combinaron dosis de 0, 112, 224, o 336 kg ha' de N, con dosis seleccionadas de K de 0,112, 224 o 448 kg ha'', sea comb KC1 o como K2SO4, dispuestas como un factorial incompleto. Se dispuso la information convenientemente en un modelo de regresiOn linear multiple y se le utilizO para pronosticar la superficie de respuesta para un factorial completo para cada fuente de K. Las aplicaciones de N incrementaron o disminuyeron los azikares reductores en los extremos apical y terminal, respectivamente. El K redujo los azficares reductores en ambos extremos del tuberculo....

We studied the effects of fertilizer N and K rates on the nutrient concentrations in petioles of Russet Burbank potato grown on a low-K, low-Cl, highly calcareous Millville silt loam soil. Phosphate and CaSO 4 were applied uniformly so that P and S did not limit plant growth. An incomplete factorial experimental design, utilizing 14 combinations of fertilizer N and K, including two forms of K, was used to develop a multi-dimensional regression model. This model was then used to produce response surfaces as an aid to analysis of the results and to illustrate the fertilizer treatment effects and their interactions on petiole chemistries. Nitrogen, K and Cl fertilizers had complex effects on petiole concentrations of N05-N, SO4-S, Cl, K, Ca and Mg. Nitrate-N and Cl were mutually antagonistic. Soil N had a large positive effect on petiole K and Mg levels and, to a lesser extent, petiole Ca levels. There was competition between K and Mg in petiole concentration. The sum of K, Ca and Mg was essentially constant across fertilizer treatments and sampling times. The sum of NO 3-N, SO4-S and Cl was highly variable. The ratio of cations to anions ranged between three and five across fertilizer treatments and sampling times. The data indicate that calibration of the major nutrient element concentrations in potato petioles, as a guide to fertilization, requires knowledge of background soil fertility conditions with respect to N, K, Cl, Ca and Mg, and an understanding of the antagonisms and synergisms among these elements. Compendio

Slow-establishing, high quality, pasture species are frequently added to standard ryegrass-white clover seed mixtures in an effort to improve pasture nutritive value. However, intense competition during establishment can suppress these species. Four alternative sowing strategies (Treatment 1: temporal separation of species (clovers sown in November 1998 before ryegrass direct-drilled at 10 kg/ha in March 1999); Treatment 2: substitution of ryegrass with slower-establishing timothy; Treatments 3 and 4: physical separation (alternate drill rows) of slower-establishing species from lower than average ryegrass seeding rates (3.5 kg/ ha or 8 kg/ha)) were used on a commercial North Otago dairy farm. Total dry matter (DM) production after 16 months was greater from pastures initially sown with ryegrass (19.1 t DM/ ha) (Treatments 3 and 4) than when ryegrass sowing was delayed or substituted with timothy (15.2 t DM/ha) (Treatments 1 and 2). The percentage of red plus white clover was similar in all pastures at 16 months of age and averaged 54%, compared with less than 1% for caucasian clover. Timothy sown without ryegrass contributed 42% of production (Treatment 2), compared with 7% when sown with ryegrass (Treatments 3 and 4). Ryegrass composition was similar (43%) regardless of sowing rate (Treatments 3 and 4) and sowing date (Treatment 1). This on-farm study demonstrated successful establishment of red and white clover in all four treatments but timothy and caucasian clover were suppressed by the inclusion of low rates of ryegrass. Keywords: botanical composition, competition, dry matter production, Lolium perenne, Phleum pratense, seeding rates, Trifolium ambiguum, T. pratense, T. repens

Band application of P fertilizer in no‐till fields results in extremely variable soil test P (STP) along lines perpendicular to the bands. This variation may be represented by two interlaced populations, each with a unique STP mean and standard deviation. The objectives of this research were to: (i) characterize STP populations in a band‐fertilized field; (ii) use these population characteristics to calibrate a Monte Carlo based model to simulate STP populations; and (iii) use simulated STP populations to evaluate different soil sampling procedures. A corn (Zea mays L.) field was band fertilized with P, and 1 yr later STP (mg P kg−1) was measured on individual soil cores with the bicarbonate extraction procedure. Out‐band STP mean and standard deviation (SD) were 13.9 ± 4.75, in‐band STP mean and SD were 127.4 ± 29.7, and composite STP mean and SD were 23.3 ± 28.69. A computer simulation model based on the Monte Carlo technique reproduced the observed populations very closely. The results show that the number of completely random soil cores needed to represent a band‐fertilized field is prohibitive. Rapid collection of a single representative composite sample with equipment capable of taking a slice of soil across the fertilizer band and accurately weight in‐band and out‐band STP by volume is recommended.