Reduced-and no-tillage seedbed preparation methods coupled with broadcast P applications lead to an accumulation of available P in the surface 0-to 5-cm soil layer and a depletion of available P deeper in the profile. A 3-yr study determined the effects of tillage and fertilizer P management on P uptake and grain yield for P-stratified soils. Tillage practices were moldboard plow (once at the start of the study followed by reduced tillage), reduced tillage (disk followed by field cultivation), and no-tillage. Four P management methods were imposed: (i) no P; (ii) 20 kg P ha 21 applied as a surface broadcast; (iii) 20 kg ha 21 applied as a banded starter, 5 cm to the side and 5 cm below the seed; or (iv) 20 kg ha 21 applied in a deep placed band, 13 to 15 cm on 0.7-m centers. The one-time moldboard plowing produced higher early season dry matter yields for corn (Zea mays L.), wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.] compared with the no-tillage system, but tillage effects on final grain yield were inconsistent. Subsurface placement of P generally increased P uptake and grain yield of corn and sorghum [Sorghum bicolor (L.) Moench], but had little effect on grain yield of soybean. Results indicate that subsurface applications of P fertilizers should be considered if soil test P is highly stratified within the surface 0-to 15-cm layer and the 15-cm composite is medium or below for available P.

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Field studies were conducted for 10 yr on a Limestone Valley soil (Dewey silt loam, a fine, kaolinitic, thermic Typic Paleudults) in north Alabama to evaluate cotton (Gossypium hirsutum L.) yield and lint quality response to long‐term surface applications of K. Potassium rates were 0,60,120, and 180 lb K2O/acre for the first 3 yr of the study. Fertilizer was broadcast in the spring or split applied in fall and spring. No K fertilizer was applied during the fourth year (1990). After the fourth year, half of the treatments were left in residual and remaining treatments continued to receive annual applications of K (1991‐1996). The experiment was a split plot arrangement of a randomized complete block. From 1987 to 1989, two varieties were compared, which served as whole plots. From 1991 through 1996, one variety was grown and annual vs. residual K fertilization served as whole plots. Potassium treatments were used as subplots throughout the test. From 1987 to 1989 there were no differences between ‘Stoneville 825’ and ‘Deltapine 50’. Lint yields were increased significantly by K fertilization in 6 of 9 yr that cotton was grown on this low K soil. Potassium fertilization increased lint yields by as much as 450 lb/acre in responsive years. From 1991 through 1996, residual K produced lesser yields than where K was applied annually. There were no differences in lint yield among split (fall‐spring), fall, or spring applied K. In responsive years, micronaire increased with K rate. Our results support the calibration currently used by the Auburn University Soil Testing Lab for Limestone Valley soils. Research Question This field study was initiated in the fall of 1986 on a Tennessee Valley soil in north Alabama that had been in alfalfa production for 5 yr. The objectives of the study were: (i) evaluate cotton varietal differences to K fertilization; (ii) evaluate cotton response to long‐term applications of K fertilizer; (iii) evaluate cotton response to annual and residual K. fertilization; (iv) determine cotton yield response to spring, fall, and split (fall/spring) application of K. fertilizer; and (v) evaluate lint quality as affected by K fertilization. Literature Summary Late season K deficiency has been observed across the U.S. Cotton Belt leading to renewed interest in soil test calibration for K in many states. In recent years, cotton response to K fertilizer rates and placement as well as foliar feeding has been evaluated. Responses of cotton to K fertilization in many of these relatively short‐term studies have been inconsistent. Previous work in Alabama has shown that cotton yields are more affected by inadequate K than soybean and grain crops. Limited data are available to describe the response of cotton to fall vs. spring applications of K. There are also limited data available to describe varietal differences in cotton response to K fertilization. Study Description A 10 yr (cotton grown 1987–1989 and 1991–1996) field test was conducted on a Limestone Valley soil (Dewey silt loam) in north Alabama. The test ...

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Technological advances in precision fertilization such as yield monitors and remote sensing are increasing the density of samples collected and decreasing the scale inputs can be managed in the field. A compounding problem is that fertilizer applications can often be made at a much smaller scale than yield data can be collected. Analytical tools such as ANOVA and geostatistics can be used on high-density data sets; however, these analytical tools do not provide all the information required to test research ideas. An alternative to solve this problem is the use of statistics not traditionally applied to precision agricultural experiments. The objective of this study was to determine if univariate distribution (population statistics) analysis is useful in the study of wheat (Triticum aestivum L.) yield response to variable-rate N fertilization strategies using active optical sensors in red and nearinfrared bands (NDVI [normalized difference vegetative index] sensors). Measurements of NDVI and fertilizer applications were on a 0.56-m 2 basis, while wheat yield data were collected at a 2-m 2 scale. Classical ANOVA was conducted to compare treatment effects. Analysis of univariate distributions for NDVI and wheat yield monitor data sets was used to further evaluate the effect of the treatments. In addition to a significant effect on the mean NDVI and yield, fetilizer staregies affected the normality, median, mode, skewness, and kurtosis of the resulting NDVI and yield distributions. Unlike ANOVA, the analyses of univariate distributions provided an insight on those portions of the NDVI and yield populations responsible for changes in the mean.