Typic Humaquept Research Articles

Effect of K fertilization on yield and leaf nutrient concentrations of potatoes grown on a sandy soil

A large percentage of winter and spring potatoes (Solanum tuberosum, L.) grown in the USA is produced in northeast Florida (NEF) on sandy soils with low cation exchange capacity. Maintaining adequate K nutrition is a major concern. A study was conducted on an Elzey fine sand (sandy, siliceous, hyperthermic Typic Humaquept) in NEF to relate yield and leaf K to soil and fertilizer K levels. In 1981, Mehlich-I soil K in the 0–15 cm depth averaged 73 mg/kg. Yields of 35 t/ha were obtained without any K fertilization and no response to K sidedressed at rates up to 70 kg/ha was obtained. In the following three years, soil K prior to fertilization was < 40 mg/kg. In 1982 and 1983, significant differences in yield were obtained as a result of K fertilization at planting at rates up to 186 kg/ha. In 1984, no yield differences were obtained with K fertilizer rates ranging from 94 to 280 kg/ha. Differences in maximum tuber yields from year to year were related to the number of growing-degree days accumulated between planting and harvest. Yield-leaf K relationships for leaf samples taken late in the season showed that the critical leaf K concentration for 35 t/ha yields was no more than about 20 g/kg; that for yields approaching 40 t/ha was no more than about 45 g/kg. The results of this study indicated that current K fertilizer recommendations are higher than necessary for the yields being obtained by most NEF potato growers.

Surface Soil Variability of a Map Unit on Niger River Alluvium

AbstractExamination of an adequate number of sample points is a prerequisite for valid generalizations in soil surveys. The number of sample points required depends upon a host of factors, including the spatial variability of the properties under investigation. This study examines the spatial variability of textural and chemical soil properties in the surface horizon of two sample areas mapped as Ozugbi series (Typic Humaquepts). From a knowledge of the dispersion characteristics of the soil properties, the number of sample points required to estimate each property at different levels of precision was determined. There were marked contrasts in the variability levels of the soil properties, and, hence, in the number of samples required to estimate each property, between the sample sites and within the map unit as a whole. The pH is the least variable of the properties examined and, hence, needs the smallest number of samples for estimation.

Exchange equilibria of potassium in soils. III. Effect of K‐fertilization on K‐Ca exchange

AbstractExchange behaviour of potassium versus calcium in relation to K‐fertilization of four soils from Bavaria, viz. Aquic Hapludalf (Kreutenbach), Aquic Chromudert (Groeben), Typic Hapludalf (Geldersheim) and Typic Humaquept (Anglberg), having a wide range after K fertilization in their cation exchange capacity and clay mineralogy was investigated. Experimental results were analysed using Q/I, thermodynamic and empirical approaches.Application of K decreased the potential buffering capacity (PBCoK) and increased ARoK in all the four soils; Q/I curves followed a second degree polynomial regression.The negative value of standard free energy of K‐Ca exchange (ΔGo) decreased with the application of K in all soils. The values of Gapon (KG) and Vanselow (KV) selectivity quotients, particularly at low K‐saturation, became small with the application of K. KV was more strongly K‐saturation dependent than KG. The experimental results have been discussed in the light of quantity and type of glycerol‐18 Å‐minerals.

Mineral Transformations in Soils Formed in Glacialmarine Drift, Northwestern Washington

AbstractThe Whatcom (Aquic Xerochrept) and Labounty (Typic Humaquept) series are soils formed in volcanic ash‐influenced, 10000‐year‐old glacialmarine drift. Surface horizons contain 5 to 10% volcanic ash; pyroxenes show pronounced cockscomb morphology, but associated hornblende is less weathered. Clay‐size minerals in unweathered drift are chlorite, smectite, mica, and in minor amounts, kaolinite and amphibole. The constant abundance of kaolinite throughout the profile and in the fresh parent drift suggests that it is not pedogenic. In the C horizon, chlorite has weathered to mixed‐layer chlorite/vermiculite (or chlorite/smectite) with 40 to 50% chlorite layers. The B horizon is dominated by chlorite, vermiculite, and chlorite/vermiculite. Smectite decreases upward and is absent from the uppermost part of the profile, where it has dissolved or possibly been converted to mixed‐layer kaolinite/smectite and chlorite/smectite.

The Effect of Lime on the Availability of Residual Phosphorus and its Extractability by Dilute Acid

Liming recommendations for acid soils are often intended to give a soil pH of 6.5. However, liming highly weathered soils to pH levels near neutrality often results in low soil P availability. The objective of this study was to determine the long-term effects of liming an acid, P-deficient Placid sand (sandy, siliceous, hyperthermic Typic Humaquept) on the availability of residual fertilizer P to potatoes (Solanum tuberosum L.). Dolomitic limestone was applied in November 1977, at rates of 0, 2,240, 4,480, and 8,960 kg/ha in a split-plot design with lime as main plots and P treatments as subplots. Phosphorus was applied at rates of 0, 56, 112, and 168 kg/ha in 1978. In 1979 and 1980, P plots were split with one-half fertilized with 56 kg P/ha and the other one-half not fertilized with P (residual). In 1978, maximum tuber yields and top dry weights occurred at the 2,240 kg/ha lime rate which resulted in a soil pH of 5.8. Plant P concentrations were unaffected by lime at any sampling date. In 1979, availability of residual soil P decreased with lime rates > 2,240 kg/ha but not enough to significantly affect yields. However, in 1980, overliming injury was observed for tuber yields at the higher lime rates which was the result of P deficiency. Application of P at planting eliminated the overliming injury with maximum yields occurring in the pH range of 6.0 to 6.5. The decrease in available P at soil pH levels above 5.5 was not accompanied by similar changes in Mehlich I-extractable P. It appears that liming to pH 6.5 in this study resulted in fertilizer reaction products that were more soluble in dilute acid but less plant available than those formed under more acid conditions. However, the Mehlich I extractant appeared to be a suitable extractant for P on this soil if pH was taken into account when interpreting soil-test P.