Rotations have long been used to improve crop yields. No‐tillage production acreage is increasing, and production information on rotation effects on yields and soybean cyst nematode populations is needed for this system. Field experiments were initiated in 1985 and continued through 1992 to evaluate P‐K fertilization effects on yield of a corn‐soybean [Zea mays L.‐Glycine max (L.) Merr.] rotation and on populations of soybean cyst nematode (Heterodera glycines Ichinohe) (SCN). The research was conducted on a Loring silt loam soil (a fine‐silty, mixed, active, thermic Oxyaquic Fragiudalf), using no‐tillage management. The experimental design was a split‐plot for corn evaluation and split‐split‐plot for soybean evaluation. Individual treatments were replicated five times. Main plots were broadcast P‐K rates of 0–0, 15–28, 29–56, 44–84, and 59–112 kg ha−1. The split‐plots were continuous corn, continuous soybean, a corn‐soybean rotation, and a soybean‐corn rotation. The split‐split‐plots were two soybean cultivars possessing different levels of SCN resistance. Yields of both crops were increased by the fertilization. In this study, corn yields were increased 14% and soybean yields increased 11% with the rotation. Rotating the two cultivars produced similar yields and nonrotated yields of resistant TN 4‐86 were higher than susceptible Essex, indicating an effect of SCN. The primary benefit of corn in the rotation was to reduce SCN populations. However, within Essex rotations the SCN population recovery was rapid, while populations remained relatively low in the TN 4‐86 rotations. The SCN populations were greater when rotations were fertilized with the two lowest P‐K rates, compared with populations within the unfertilized check and the highest P‐K rate. Soybean producers should consider a no‐tillage system of rotating corn with SCN‐resistant soybean cultivars, fertilized at high P and K rates for yield improvement and reduced SCN populations.
Correcting K deficiency in fast‐fruiting cotton (Gossypium hirsutum L.) cultivars requires information on growth response to available soil K, soil K2O rates, and supplemental foliar K. Field research was initiated in 1991 on a Memphis silt loam soil (fine‐silty, mixed, active, thermic Typic Hapludalf), low in Mehlich I extractable K, to evaluate cotton responses to soil‐and foliar‐applied K for conventional‐tillage (CT) and notillage (NT) production systems in Tennessee. Potassium rates of 0, 30, 60, and 120 lb K2O/acre were soil‐applied to the same plots each year. Foliar treatments included: no‐foliar K, KNO3, and Ca(NO3)2. KNO3 was applied four times per year to supply 4.4 lb K2O/acre per application. Ca(NO3)2 was applied at 1.4 lb N/acre per application, equalling the N applied in the KNO3 foliar applications. Petiole K concentrations were evaluated for each foliar application. Soil samples (0–6 in.) were collected after harvest from the no‐foliar K treatments of each main plot to evaluate Mehlich I extractable soil K. Lint yields were determined by mechanically picking the two center plot rows twice each year. Extractable soil K increased linearly with increased soil K2O rates each year for both tillage systems. Yields in both tillage systems were increased by soil‐ and foliarapplied K. Regression equations expressing yield as a function of K2O rate were developed for KNO3 and no‐foliar K treatments each year for both tillage systems. In 1991 and 1992, the foliar KNO3 treatment increased yields at all soil K2O rates. In 1993, foliar KNO3 increased yields at soil K2O rates up to 94 lb K2O/acre in CT and up to 103 lb K2O/acre in NT. In addition, foliar KNO3 increased yields at soil K2O rates up to 108 lb K2O/acre for the 1994 NT cotton. Relationships found between Mehlich I soil extractable K and soil K2O rates were used to calculate the critical soil extractable K levels for predicting yield response to foliar K. These values ranged from 158 to 161 lb K/acre and correspond to the 160 lb Wacre value used to distinguish between medium and high testing soils in Tennessee. For this soil, foliar K supplemented soil K2O rates and increased yields when extractable K was medium or lower. Moreover, petiole K concentrations indicated plant K was deficient in 1991 and 1992 at all K2O rates and was deficient in 1993 for K2O rates of 60 lb/acre or less. Research Questions Potassium deficiency may limit yields of certain high yielding, fast‐maturing cotton varieties. Information is needed on K fertilizer requirements to correct deficiencies on low testing soils. What are the optimum combinations of soil and foliar K applications on a low extractable K soil for conventional‐ (CT) and no‐tillage (NT) cotton? What is the relationship between soil‐applied and foliar K for increasing lint yields on a low K soil? Literature Summary Visual K deficiency symptoms in cotton have been observed in the new vegetative growth of fast‐fruiting varieties. Deficiencies occur as the boll load is set over a short growth period and when root ...
Utilization of wheat (Triticum aestivum L. em Thell.) as a cash crop or cover crop in a double‐cropping system is desirable to prevent excessive soil erosion on loess‐derived soils in the southern USA. Fall and spring N application to winter wheat double‐cropped following grain sorghum (Sorghum bicolor L.) was evaluated on a Grenada silt loam (fine‐silty, mixed, thermic Glossic Fragiudalf). The experimental design was a randomized complete block with a split‐plot arrangement of treatments. Rates of N applied at planting; (0, 34, and 67 kg ha−1) were the main plots, with N rates applied in the spring (0, 34, 67, 101 and 134 kg ha−1) the sub‐plots. Fall N (Nf) increased both yield and plant height. Spring N (Ns) had a. greater effect on yield and plant height than Nf. Yields increased from 0.83 to 2.61 Mg ha−1) by increasing Ns from 0 to 134 kg ha−1) without Ns. Yields increased from 1.50 to 2.67 Mg ha−1) by increasing Na from 0 to 67 kg ha−1 with 67 kg ha −1>/ Nf. Yield variation was expressed by Y = 0.822 + 0.0098 Nf + 0.0248 Ns − 8.5 × 10−5) N2s + 1.45 × 10−5 NfNs − 7.41 × 10−7 NfN2s. Plant height increased from 56 to 85 cm by increasing Ns from 0 to 134 kg ha−1 without Nf, but increased from 67 to 80 cm by increasing Ns from 0 to 67 kg ha−1 with 67 kg ha−1 Nf One‐hundred‐kernel weight decreased from 2.35 to 2.11 g by increasing Ns from 34 to 134 kg ha‐1. Grain N increased from 19.9 to 23.2 g kg‐1 by increasing Ns from 34 to 134 kg ha−1.
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