No abstract

Although use of micro‐irrigation has risen steadily in Georgia, few studies have been reported describing its effect on yield or rooting distribution of tomato (Licopersicon esculentum). The objective of this experiment was to determine the effects of mulch type (plastic mesh and straw) and micro‐irrigation on soil physical properties and growth of ‘Celebrity’ tomato. In 1986, an experiment was initiated on a Cecil sandy loam (clayey, kaolinitic, thermic, Typic Kanhapludult) at Griffin, GA. Tomato yield and root growth, soil temperature, and water potential in 1987 and 1988 were compared using black plastic mesh and straw mulches and three micro‐irrigation frequencies: control (no irrigation), daily, and twice weekly. Soil properties beneath the two types of mulches were compared in terms of surface evaporation, measured during 24‐h periods several times each year and bulk density, organic C, pH, infiltration rate, and cone index measured at the end of the 1988 growing season. Straw mulch resulted in a significantly greater infiltration rate, and lower pH, bulk density, surface evaporation, cone index, soil temperature and matric potential than the plastic mulch. Yields were higher under the straw mulch compared to the plastic mulch and irrigation increased yield with a straw mulch in 1987 but not 1988. Yields were not increased by irrigation of the plastic mulch treatment. Straw mulches have the potential to improve tomato yields in high‐temperature environments, provided soil pH is controlled.

To serve as a useful guide to fertilizer management, a nutrient diagnostic method should identify cases in which a nutrient limits yield, as well as cases in which the nutrient does not limit yield. Erroneous diagnoses can lead either to unnecessary fertilizer application or failure to apply fertilizer when a yield response would result. We propose a process of prescient diagnostic analysis to evaluate the utility of diagnostic methods based upon comparing individual diagnoses to corresponding responses to fertilizer applications. A nutrient diagnostic method is evaluated upon the incidence and yield consequences of its true and false positive and negative diagnoses. Evaluation criteria integrate these effects to facilitate comparison of various diagnostic systems. We propose a protocol for evaluating diagnostic methods based upon this reasoning.

The Diagnosis and Recommendation Integrated System (DRIS) provides advantages over the Sufficiency Range (SR) approach to diagnosing the nutrient status of soybean (Glycine max L.).However, a number of modifications to DRIS have been proposed, including the use of only one method for calculating nutrient indices, and incorporating nutrient concentrations. In previous research, the author found that derivation and interpretation of DRIS diagnoses could be simplified by: 1) using a logarithmic transformation of nutrient ratio data; 2) using population parameters rather than high-yield subpopulation values; 3) using a single index calculation method; and, 4) incorporating a measure of 901 902 BEVERLY the probability of yield response to a treatment. Diagnoses by the SR approach, DRIS, three revisions of DRIS, and two new concentration-based diagnostic methods were compared using diagnostic norms derived from a data base of over 4000 soybean tissue analyses and yield observations. Virtually all diagnoses of the most limiting nutrient were the same, except that the SR method did not make diagnoses on 5 week-old samples. Traditional DRIS diagnoses were the least conservative, indicating only the order in which N, P and K would likely limit yield. Revised methods, particularly the concentration-based methods, indicated fewer limiting nutrients, and agreed well with the SR method. Yields in the test data set increased with nearly every nutrient application, so the least conservative DRIS showed the greatest yield advantage.No diagnostic method consistently identified the nutrient causing the greatest yield response as most limiting.

Fertilizer and irrigation must be managed for efficient resource use and preservation of environmental quality as well as maximum production. Two furrow irrigation experiments growing broccoli (Brassica oleracea) were conducted. The first consisted of three N rates (90, 180, and 270 kg/ha), two irrigation treatments (replenishment of water lost by evapotranspiration and evapotranspiration plus 30%), and two N application procedures (application to the soil and in the irrigation water) on a sandy loam soil (coarse‐loamy, mixed, thermic Typic Xerofluvent). Plant growth increased with increasing N application. For a given N application, there was higher average production with the lesser amount of water application. The method of N application had very little effect on production under the lower irrigation treatment, but production was consistently higher for N application with water rather than to the soil when the higher water application treatment was used. The ratio of N in the plant to N applied decreased with increasing N application, decreased with higher water application, and decreased with application in the irrigation water as compared to soil application. The second experiment consisted of two N rates (115 and 225 kg/ba) and two N application procedures (application to soil and in the irrigation water) on a loam soil (fine‐loamy mixed, thermic Calcic Haploxeroll). Yield and N uptake were significantly higher with 225 as compared to 115 kg/ha of N. Conventional preplant and side‐dress N application to the soil resulted in significantly higher broccoli head yield than injecting N in the irrigation water. Leaching of N was not a factor under the experimental conditions.