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Highly weathered soils in the southeastern USA often have very acid, hard, infertile subsoils not readily penetrated by crop roots. An experiment on a Typic Hapludult involving deep liming, subsoil disturbance and mixing, and surface application of gypsum was conducted to investigate the possibilities of ameliorating such subsoils. Results with alfalfa (Medicago sativa L.) over 4 yr show that liming to 1 m can increase yields by 50% while merely mixing the subsoil without lime incorporation resulted in a substantial yield decline. Surface application of gypsum with sufficient time for it to penetrate the subsoil resulted in 25% yield increases. Deep liming resulted in the complete precipitation of soluble Al and increased the level of soluble Ca allowing roots to freely penetrate the subsoil. Gypsum resulted in a progressive reduction in soluble Al and an increase in soluble Ca creating a similar but lesser effect than liming. Water extraction patterns corroborated the fact that roots were penetrating chemically ameliorated subsoil. Saturation extract studies indicated that gypsum reduced the activity of Al3+ and increased that of Ca2+ substantially. These results suggest that by‐product gypsum from phosphate acid manufacture would be a feasible amendment for acid subsoils.

The spatial variability of soil properties that affect the soil N budget and corn (Zea mays L.) grain yield were studied for 2 yr in south‐central Texas to better assess the potential for variable‐rate N fertilization. Residual soil NO3–N with depth and soil N mineralization (Nmin) potential and their relationships with soil total N, soil organic C, and clay content were characterized. Residual soil NO3–N to 60‐cm depth was more related to corn yield than NO3–N at shallower depths. Residual soil NO3–N showed temporal variation with spatial structure existing for NO3–N in the first year when NO3–N concentrations were high, but this variation was absent in the second year when NO3–N concentrations were low. The opposite trend was observed for soil Nmin. Soil total N exhibited temporal persistence. Soil Nmin showed significant correlations with soil clay content in both years. Temporal persistence of soil texture and variation in spatial structure for N parameters would likely result in different strategies for soil N management zones in 2002 vs. 2003. This experiment demonstrated the potential importance of soil texture for modifying fertilizer N recommendations. Texture generally is more easily determined than soil N parameters at the scale and intensity necessary for site‐specific N management.

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