Preplant N fertilizer applications on sandy Coastal Plain soils are often less efficient than sidedress N applications due to leaching of NO−3 from the rhizosphere. Preplant‐incorporated broadcast applications of ammoniacal N fertilizers containing the nitrification inhibitor nitrapyrin [2‐chloro‐6(trichloromethyl)pyridine] should increase utilization of the exchange capacity of sandy soils to retain NH+4 and increase preplant N fertilizer efficiency. The effects of N rate, N source, and nitrapyrin on inorganic soil N form, soil N content, and corn (Zea mays L.) growth were investigated in 1977 on a Marlboro sand (Typic Paleudult) and a Varina loamy sand (Plinthic Paleudult) and in 1978 on a Wagram sand (Arenic Paleudult). Nitrogen treatments consisted of a zero‐N check, preplant broadcast applications of 56, 112, 168, and 224 kg N/ha as urea, 112 kg N/ha as NaNO3, and 112 kg N/ha as urea plus 1.12 kg nitrapyrin/ha dissolved in water. Soil N measurements at 34, 40, and 48 days after N treatment application on the Marlboro, Varina and Wagram soils, respectively, showed that nitrification was suppressed by nitrapyrin. The lack of significant differences in inorganic soil N contents in the 0 to 15 cm depth among 112 kg N/ha supplied as urea with and without nitrapyrin and NaNO3 indicated that little leaching occurred in 1977. Leaching conditions in 1978 resulted in large losses of inorganic N from the rooting zone; however, when nitrapyrin was added with urea, losses of N were significantly reduced. High N rates from urea decreased the pH in all soils except when nitrapyrin was included. In 1977, inclusion of nitrapyrin with urea had little effect on leaf N, grain yields, plant N accumulation or N fertilizer recovery due to small losses of soil inorganic N. However, in 1978 when leaching conditions occurred, nitrapyrin with urea decreased soil N losses, significantly increased leaf N concentration, grain yields, plant N accumulation and N fertilizer recovery.
Tillage pans in sandy coastal plain soils often restrict utilization of subsoil moisture and nutrients and may limit corn (Zea mays L.) yields. Field experiments were conducted for 2 years on a Wagram loamy sand (Arenic Paleudult) with a tillage pan to evaluate deep tillage treatments and preplant N applications containing nitrapyrin (NI) on corn. Experiments were arranged in a split plot design containing three tillage treatments as the main plots with four N‐treatments as the subplots. The three tillage treatments were: a) disking to a 15 cm depth, designated as conventional, b) chisel‐plowing to a depth of 30 cm at 30 cm intervals, and c) subsoiling in the row to a depth of 45 cm and bedding over the subsoil slit. Four N‐treatments consisted of preplant applications of 0, 112, and 168 kg N/ha broadcast as urea and a urea‐NI solution at a rate of 112 kg N/ha plus 1.12 kg NI/ha. Measurements were made of soil NH+4 and NO‐3 concentrations, leaf N, stover weight, stover N concentration, grain yield, grain N content, and recovery of fertilizer N. Use of NI in 1978 resulted in more of the total inorganic soil N in the 0 to 15 cm depth being in the NH+4 form; however, this did not significantly increase total inorganic soil N content at any depth. Nitrapyrin had no significant effect on inhibition of nitrification in the top 45 cm depth in 1979. Inorganic soil N was moved below the tillage pan into the subsoil by leaching rains. Ineffectiveness of NI to significantly suppress nitrification in 1979 was probably due to the differential movement of NH+4 and NI. Subsoiling significantly increased leaf N concentration above that obtained from conventional tillage in 1979, suggesting root extraction of soil N below the tillage pan. Chisel‐plowing and subsoiling increased corn stover dry matter production above that of the conventional tillage in both seasons. Disruption of the tillage pan by subsoiling or chisel‐plowing increased corn yields above that obtained with conventional tillage. Highest yields were obtained with subsoiling. In 1978, higher grain yields with the deep tillage treatments were thought to have resulted from the utilization of moisture below the tillage pan. Increased yields with deep tillage in 1979 were due to utilization of both moisture and N below the tillage pan. Yields in 1978 were significantly higher with 168 kg N/ha as compared with 112 kg N/ha rate. Yields in 1979 were not significantly different at the 112 and 168 kg N/ha rates. Nitrapyrin had a positive effect only on yields with the chisel‐plow treatment.
Limited literature is available to provide recommendations of K source and rate and P rate for sweet potato [Ipomoea batatas (L.) Lam.] production. Many growers, therefore, continue to use the more expensive sulfate (SO4) source of K rather than chloride (Cl) and higher than recommended rates of K and P. Accordingly, on‐farm experiments were conducted during 3 years on North Carolina Paleudults to determine effects of K source and rate and Prate on sweet potato yield, grade, and quality. Potassium sources were KCl and K2S04. Fertilization rates of K varied over the five K experiments and depended on initial soil test levels which ranged from 0.04 to 0.12 cmol K L−1 by Mehlich‐I extractant. In the three P experiments, the various P rates were also dependent upon the initial soil test levels which ranged from 11 to 30 mg P L−1 also by Mehlich‐I extractant. As K source had no effect on yield, grade, or quality, it was concluded that the higher Cl concentrations, up to 22.8 g kg−1, in vegetative tissue with increasing KCl rates had no detrimental effect on sweet potato yield, grade, or quality. Total yield response to K applications was obtained where soil test K levels were ≤ 0.08 cmol L−1, although no. 1 yields increased only where soil test K levels were ≤ 0.05 cmol L−1. Phosphorus applications had no effect on yield, grade, or quality of sweet potato.
Analysis of samples of four profiles, two containing calcareous shale and two acid shale, from a coal mine in Iowa showed that the total S content of the coal seam under acid shale ranged from 9 to 10% and of the coal under calcareous shale was about 5%. Zinc‐HCl‐reducible S always exceeded the Raney Ni‐reducible S in all the samples studied. With the exception of one coal sample under acid shale that contained an appreciable amount of sulfide S, all the shale and coal samples contained small amounts of sulfide S. The shale samples generally contained greater amounts of pyrite S (52–85%) than did the coal samples (35–63%). Pyrite S was significantly correlated with total S in the shale (r = 0.95**) and coal (r = 0.93**) samples studied. Other results indicated that total N values were much lower in the overburden materials (0.01–0.13%) than in the coal samples (0.65–0.81%). Total P content was the greatest in the shale samples. The coal seam under acid shale contained greater P concentrations, with the organic P fraction exceeding the inorganic P, than did the coal seam under the calcareous shale, where the amounts of organic and inorganic P fractions were similar. The sulfur fractions in the various horizons of the four profiles studied and the relationships among organic C, N, and P are discussed.
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