Soil penetration resistance scone index) varies with water content. The field variation of water content could mask treatment differences. The correction of cone index data to a sin g le water content would help prevent this. We used equations from . TableCurve software and from the literature to correct cone indices for differences in soil water contents. Data were taken from two field experiments where cotton (Gossvpzum hirsutum L.) was grown usin g conventional and conservation tillage without irri g ation. and beans ( Phaseolus uuiearis L.) were grown using conventional tillage with microirri gation. Boundary conditions based on hard, dry and soft. wet ;oils were imposed on the equations. Equations tit the data with coefficients of determination ranging from 0.55 to 0.92 and error mean squares from 1.37 to 6.35. After correction, cone index dependence on water content was reduced. A sin g le-equation correction did not always fit the data across all treatments. Separate corrections, based on treatment. mi ght be required. When corrections required multiple equations. differences may be real or may be a manifestation of the correction differences. in this case, the correction may not be feasible (unless some future work can coordinate different equations and assure a uniform correction).1997 Elsevier Science B.V.

Lack of water because of erratic rainfall frequently limits corn (Zea mays L.) production on Typic Paleudults in the Atlantic Coastal Plain. Traditionally, wide (96 cm) row spacing and low plant population have been used to prevent water stress, but recently landowners have begun to invest in irrigation systems. Changes in row spacing, plant population, or fertilization practices may be required to achieve maximum water‐and nutrient‐use efficiency with those systems. We evaluated plant population treatments averaging 7.0 and 10.1 plants m−2 in single and twin rows on a Norfolk (fineloamy, siliceous, thermic Typic Paleudult) loamy sand during 1980, 1981, and 1982. Three water management [nonirrigated, irrigated using tensiometers (TENS) to measure soil‐water potential for scheduling, and irrigated using a computer‐based water balance (CBWB) for scheduling], and two fertilization programs were also evaluated in a four‐factor split‐plot design. Water management and plant population interacted significantly. Planting in twin rows increased grain yield an average of 0.64 Mg ha−1 (10 bu/A), but planting more than 7.1 plants m−2 significantly increased grain yield only in 1980. Irrigation increased grain yield 150, 161, and 8% in 1980, 1981, and 1982, respectively, as a result of increased kernel weight and number of kernels per ear. Increasing total N, P, and K application beyond 200, 30, and 167 kg ha−1, respectively, did not significantly influence grain yield or yield components. Yield advantages of narrow rows can be obtained on Coastal Plain soils which require subsoiling by using a twin‐row planting configuration. Irrigation can be scheduled using either tensiometers (soil‐water potential) or a computerized water balance without significantly changing corn grain yield, nutrient accumulation, or yield components.

The flowering stage is the key yield determinant period of soybean. Short-duration water stress occurring during this stage significantly reduced soybean development and final productivity. Seed treatment with uniconazole powder application plays an important role in alleviating the adverse effects of dry soil on plant development. In order to explore effects of uniconazole on soybean morphological characteristics and yield under drought stress, different rate of uniconazole powder were examined under developing gradually drought stress during flowering stage. The yield of soybean decreased under drought, uniconazole application increased yield. All results suggest that 4 mg/kg is the optimal uniconazole application rate under drought for soybean at the flowering stage.

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The maximum amount and rate of nutrient accumulation by irrigated corn (Zea mays L.) must be known so that farmers do not waste money or pollute water resources by applying excessive amounts offertilizer. Aerial whole plant samples were therefore collected from irrigated field experiments conducted on Norfolk (Typic Paleudults) loamy sand in t980, t98t, and t982, to determine seasonal dry matter, N, P, and K accumulations for corn yielding tO Mg ha-1 or more in the southeastern Coastal Plain. Rates of accumulation were derived by differentiating compound cubic polynomial equations that described seasonal accumulation patterns. Total dry matter accumulation averaged 23.t and 24.9 Mg ha-1 for two population treatments that averaged 7 X t0 4 or tO X t0 4 plants ha-1 • Aerial N, P, and K accumulation respectively averaged 228, 58, and 258 kg ha-1 in t980; 264, 37, and 372 kg ha-1 in t98t; and 225, 37, and 335 kg ha-1 in t982. Grain yields averaged t3.4, 11.7, and tO.~ Mg ha-1 in t980, t98t, and t982, respectively. Lower P accumulations in t98t and t982 were the result of lower grain yields that were apparently caused by excessive K accumulation. Calculated peak dry matter, N, P, and K accumulation rates were 650, tO, 1.6, and 28 kg ha-1 day-1 in this study, compared to rates of 247, 4.5, 0.6, and 3.2 kg ha-1 , respectively, in previous midwestern studies. Peak accumulation rates during both vegetative and reproductive growth stages emphasize that cultural, nutrient, and water management practices must be coordinated to provide a minimum stress production environment for high corn yield.