Differential effect of carbon sources on nitrogen transformation in Hawaiian soils
SummaryMineralization of native N was curtailed by addition of carbon sources in all soils tested. A readily available energy source, sucrose, accelerated and increased the immobilization of native as well as added N more than a slowly available energy source, sugar cane bagasse. Addition of N as ammonium sulfate increased CO2 production in only one out of five soils when no energy source was added. With energy source addition, N addition enhanced CO2 production in most soils. Without any treatment, the immobilization of added N was related to the C:N ratio of the soil; maximum immobilization occurred in the soil with the widest C:N ratio.
Effect of Douglas-Fir Sawdust Mulches and Incorporations on Soil Microbial Activities and Plant Growth1
Sawdust and other wood wastes applied to soil may retard plant growth by inducing nitrogen deficiency but these effects with Douglas-fir are less pronounced than with many other residues of wide C:N ratio. While Douglas-fir wood is extremely low in nitrogen it is low also in available carbon. The predominating lignin-cellulose complex is resistant and only slowly metabolized, enabling a minimum amount of nitrogen, repartitioned among successive crops of microbes, to suffice for long-continued decomposition. Sawdust showed no direct toxicity and had little effect on soil pH. Resins and other extractives were readily decomposed. Apparent decomposition percentages based on 50 days CO₂ production without added available nitrogen in soil respiration experiments were: for dextrose 60, wheat straw 48, red alder 40, ponderosa pine 33, western red cedar 33, Douglas-fir 30, pitch 30, western hemlock 27, bark 26, and lignin 6%, respectively. Although added nitrogen fertilizer hastened decomposition of organic matter having wide C:N ratio, it commonly depressed cumulative CO₂ evolution in soil respiration. Greenhouse and field studies indicate that to avoid induced nitrogen deficiency 5 to 10 pounds of nitrogen per ton of sawdust are generally sufficient during the first year; nitrogen additions the following 2 or 3 years may be successively halved. Douglas-fir sawdust without added nitrogen often causes no retardation and in some cases significant increases of certain crops such as sunflowers and strawberries. Corn appeared much more sensitive to nitrogen deficiency. All wood wastes and cereal straws at 100 tons per acre have been found to depress plant growth unless nitrogen is added.
LABORATORY AND FIELD TESTING OF SEED SPACING UNIFORMITY FOR SUGARBEET PLANTERS
Five planter configurations were evaluated for seed spacing uniformity at three field speeds using a seed 
location method in the field and a laboratory method involving an opto-electronic sensor system. Planter seed spacing 
uniformity was described using the Coefficient of Precision (CP3) measure. Results showed that CP3 measures 
determined using the laboratory test method were significantly different from those determined using the field test method. 
This indicated the laboratory test method cannot be used to predict planter seed spacing uniformity in the field. Seed 
spacing uniformity determined in laboratory tests was higher than, or equal to, seed spacing uniformity determined in 
field tests. This indicated the laboratory test method may be useful to screen out planters or planter units with poor 
uniformity of seed metering. Field testing of the planters that perform well in laboratory tests must be conducted to 
adequately determine the seed spacing uniformity of those planters in the field. Results from laboratory and field tests 
could be useful in determining areas for improvement of planters or planter units.