Investigation of the spatial arrangement of plant roots in soils is limited by the time required to remove the roots from the soil and measure the viable roots. A root measurement technique is reported which includes differentially staining viable root tissue and extraneous organic matter with trypan blue, photographing the roots, and presenting the photographic negatives to an Image Analyzing Computer, which can predict root length or area in seconds. The staining procedure did differentially stain the viable roots and organic matter since addition of dried organic matter did not increase the Image Analyzer estimation of length or surface area. The photographic process, however, contributed to lower and more variable Image Analyzer estimates of root surface area when comparing specimens presented as photograhic negatives or in bulk without photography. The Image Analyzer provides reliable estimates of surface areas for root and wire samples presented in bulk with a coefficient of variation of 3.3 and 1.2%, respectively. This technique is relatively rapid and can be used to measure plant root systems sampled by soil cores.
Potato plants were grown 3 different years in noncompacted, moderately compacted, and severely compacted soils. Changes in yield and quality of tubers were measured against different levels of N and P and against soil moisture tension.
Total and U. S. No. 1 tuber yields were affected adversely by compacted soil. Tuber deformity was confined to angular development conforming to the shape of adjacent clods. Second growth and growth cracks in tubers were of no consequence. No consistent change in specific gravity was found.
Neither yield nor quality of the tubers was enhanced by use of N higher than 180 pounds per acre. Addition of P had no appreciable effect. Soil P reserves were high.
Tuber yield and quality in all soils were best when the soil moisture tension was near 0.5 atm. At a lower tension (0.2 atm) enlarged lenticels were more prevalent, and at a higher tension (0.7 atm) the yield and percent of U. S. No. 1 tubers diminished in severely compacted soil. Without proper control of the soil moisture regime in compacted soils, loss in tuber yield and quality could be accentuated.
Neither changes in fertilizer nor irrigation practices alleviated the adverse effects of soil compaction on potato yield or quality.
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