Transport of soluble organic and inorganic carbon in sandy soils under nitrogen fertilization

Leaching of water soluble soil carbon plays an important role in downward transport of soil nutrients and pollutants and may be influenced by soil and management factors. We examined the leaching of water soluble carbon from two sandy soils under nitrogen fertilization by adapting an intermittent leaching-incubation technique using packed soil columns (94 × 10 cm). After 30 d, cumulative amounts of water-soluble organic carbon (SOC) leached from the Candler and Wabasso sand for various treatments in mg C column−1 were: 77 and 302 (NH4NO3), 64 and 265 (control), and 45 and 239 (isobutylidene diurea, IBDU), respectively. The IBDU and NH4NO3 treatments increased the leaching of water-soluble inorganic carbon (SIC), which ranged from 2 to 38 mg C column−1 over 30 d. At the end of eight cycles of leaching/incubation, the total carbon content increased at depth (control and NH4NO3 treatment) in the Candler sand, but decreased in the Wabasso sand. In the first leaching event, the average rate of SOC leaching from the Wabasso sand was 26 mg C column−1 d−1 which dropped rapidly to about 5 mg C column−1 d−1 towards the end of the experiment. The rate of SOC leaching from the Candler sand was much lower (<8 mg C column−1 d−1) than the rate of SOC leaching from the Wabasso sand. Compared with the unamended treatments, application of NH4NO3 increased and IBDU decreased the leaching of SOC in both soils. These effects of N application were considerable during the initial two to three leaching events only. Our results suggest that the initial rainfalls that follow a dry period may be critical for transporting SOC from the upper layer of these sandy soils. Key words: C leaching, sandy soil, intermittent leaching condition, isobutylidene

Late-season Applications of Various Nitrogen Sources Affect Color and Carbohydrate Content of `Tiflawn' and Arizona Common Bermudagrass

Bermudagrass turfs in the southern United States often receive late growing season applications of nitrogen (N) in order to sustain turfgrass color prior to dormancy, even though such applications might increase winterkill potential. Yearly research trials were initiated in the last week of Sept. 1989 to 1991 at Mississippi State Univ. to evaluate fall and spring color responses and rhizome levels of total nonstructural carbohydrates (TNC) of `Tiflawn' and Arizona (AZ) Common bermudagrass [Cynodon dactylon L. (Pers.)] treated with various N sources delivering N at 98 kg·ha-1 in a single application. The fertilizers were ammonium nitrate (AN), sulfur-coated urea (SCU), a natural organic (`Milorganite', NO), isobutylidene diurea (IBDU), ureaformaldehyde (UF), and methylene urea (MU). Color responses from N fertilization were most prominent in the fall except when there was an early frost event in Oct. 1990. The most rapid greening response and highest color ratings were consistently observed for the water-soluble AN. Of the slow-release sources, SCU, MU, and IBDU provided color responses as long as temperatures remained warm enough to promote bermudagrass growth. The NO source provided an unexpected, significant greening response in Oct. 1989 and 1991 on `Tiflawn', but not on AZ Common. The UF consistently provided the lowest color ratings. There were virtually no differences in TNC levels between N treatments for either grass. At no time was there any indication that N fertilization increased bermudagrass winterkill potential; to the contrary, the predominant responses were better fall and spring color than the nontreated control.

Effect of Natural Organic Nitrogen Fertilizers on Hybrid Bermudagrass Growth

Eco, Milorganite, Ringer, and Sustane natural organic fertilizers, alone or combined with the synthetic organic fertilizer isobutylidene diurea (IBDU), were compared with IBDU alone for their effect on a `Tifdwarf' hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] golf course putting green. Over the 2-year study period, no consistent differences were observed among the fertilizer treatments on the turfgrass growth parameters of quality, clipping weights, or root weights.

Efficiency of Isobutylidene Diurea, Sulphur-Coated Urea and Urea Plus Nitrapyrin, compared with Divided Dressings of Urea, for Dry Matter Production and Nitrogen Uptake of Ryegrass

SummaryTwo slow-release nitrogen fertilizers, isobutylidene diurea (IBDU) and sulphur-coated urea (SCU), and urea plus nitrapyrin were compared with urea alone for their effect on the growth and nitrogen uptake of ryegrass in a greenhouse experiment.The IBDU and the SCU were applied in one dressing before sowing and the urea in five dressings (one after each cut). Dry matter yield and nitrogen uptake of the six cuts at the optimum levels of 3 and 6 g N pot−1 (equivalent to 1120 and 2240 kg N ha−1 on a weight basis) were similar for the slow-release fertilizers and urea, showing that SCU and IBDU can be effective sources of nitrogen for ryegrass at rates far above those regarded as safe for conventional nitrogen fertilizers when applied in a single dose.Nitrapyrin at 20 ppm effectively inhibited nitrification for 12 weeks, then its effect rapidly declined, disappearing after 18 weeks. Ryegrass growth was retarded by nitrapyrin treatment, probably as a result of an accumulation of NH4-N in the soil.

Supplementation to improve the production of yearling steers grazing poor quality forage. 2. The effects of oats, supplementary nitrogen, lupins and cottonseed meal

Four supplements were compared in an experiment in which yearling Hereford steers were grazed on mature annual pasture for 84 days and fed, at levels of 0, 300, 600 and 900 g/steer.day, supplements of pelleted cottonseed meal, lupins, oats + isobutylidene diurea (IBDU) or oats alone. The supplements increased growth rates from - 2 14 (no supplement) to 321, 119, 47 and 47 g/steer.day respectively (900 g/ steer.day). The cottonseed meal supplement produced significantly better growth rates than the other three supplements, the responses to which did not differ significantly. During a period of 111 days after supplementation, when all steers were lot-fed as one group prior to slaughter, there was substantial, but not complete compensatory growth and a significant inverse relationship between growth during supplementary feeding and growth during the next 111 days. There were, however, no significant differences in growth during lot-feeding, carcass weights, dressing percentages or carcass fatness associated with the previous supplementary feeding treatments. The effects of five different supplements (including the four mentioned above) on the intake of a poor quality roughage by weaner lambs were compared in a preliminary pen-feeding experiment. The supplements (pelleted cottonseed meal, lupins, oats + IBDU, oats + urea, and oats alone) significantly improved roughage consumption by 26-49%. There were no significant differences between supplements.

Effect of nutrient seed coating on the emergence and early growth of perennial ryegrass

Perennial ryegrass (Lolium perenne L.) seeds were coated with either lime, reverted superphosphate plus nitrogen as isobutylidene diurea (RSN), or partially acidulated rock phosphate plus sulfur (ESPARP). In one experiment emergence rates and total emergence were calculated by fitting Mitscherlich-type curves to the data and then conducting statistical tests on the three parameters found for each curve. There was a significant interaction between soil moisture and coating treatment for all three parameters. In a glasshouse experiment, the same coated and uncoated seed treatments were sown either in soil supplied with nitrogen, phosphorus and sulfur or in soil with nutrient deficiencies of either N, P, or S or NPS, and the early growth of the plants and their P and N uptakes were studied. The two nutrient-coated treatments (RSN and ESPARP) produced more tillers and dry matter yields of roots and shoots than did lime-coated or uncoated seed when grown in soils deficient in P, S or NPS. Nitrogen deficiency reduced yields of all plants, even those derived from RSN seeds. N uptake in the RSN treatment was not significantly different from the ESPARP treatment, indicating that the N in isobutylidene diurea was not available to the plant.

Effect of green manures on yield and nitrogen requirement of sugar beet

SUMMARYFour field experiments in 1972–6 investigated the effect of undersowing trefoil or ryegrass in barley, and of fodder radish sown after barley, on yield and nitrogen requirement of following sugar beet. Autumn applications of isobutylidene diurea or glycoluril (slow-release nitrogen fertilizers) were also included for comparison with green manures. The plots were split in the following spring and dressings of 0, 50, 100 and 150 kg N/ha as ‘Nitro-Chalk’ tested on the sugar-beet crop.The undersown green manure crops slightly decreased the yield of barley but, at the time of ploughing, returned up to 3·7 t dry matter/ha and 50 kg N/ha. In the absence of spring-applied nitrogen fertilizer for the sugar beet, green manures increased root and sugar yield, but when more than 50 kg N/ha was applied for the sugar beet they had no effect on yield. Autumn applications of nitrogen fertilizers such as isobutylidene diurea decreased the requirement for nitrogen in spring, but yields were no greater than from spring-applied nitrogen alone. Top and subsoils sampled in late winter and early summer from plots where green manures had been grown showed no detectable increase in soil organic carbon or total nitrogen, but soil mineral-nitrogen concentrations were increased slightly by green manures as was the potentially available mineralnitrogen released in an incubation test. It is concluded that, on loamy soils, green manures decrease the nitrogen requirement of sugar beet but give no benefits in yield which cannot be obtained from nitrogen fertilizer in spring before sowing the crop. assistance and Miss G. Smith for statistical analyses.