Effect of seed-placed urea fertilizer and N-(n-butyl)thiophosphoric triamide (NBPT) on emergence and grain yield of barley

Transcription

1 Effect of seed-placed urea fertilizer and N-(n-butyl)thiophosphoric triamide (NBPT) on emergence and grain yield of barley C. A. Grant and L. D. Bailey Agriculture and Agri-Food Canada, Brandon Research Centre, Box 1000A, R.R.#3, Brandon, Manitoba, Canada R7A 5Y3. Received 10 November 1998, accepted 28 April Grant, C. A. and Bailey, L. D Effect of seed-placed urea fertilizer and N-(n-butyl)thiophosphoric triamide (NBPT) on emergence and grain yield of barley. Can. J. Plant. Sci. 79: Seedling damage from excess seed-placed urea fertilizer can be a major problem in one-pass seeding and fertilizing systems. Field studies were conducted on a clay loam and a fine sandy loam soil over 3 yr to evaluate the impact of seed-placed urea N, with and without the addition of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) on stand density and growth of barley. Seedling damage, as indicated by reduction in stand density, occurred on both soil types at rates of seed-placed N as low as 40 kg N ha 1. Addition of NBPT to the urea fertilizer increased stand density at N levels where damage occurred with the untreated urea. Dry matter yield at heading generally was unaffected by N application or use of NBPT; however, final yield was increased by use of NBPT in four of five site-years. Use of NBPT appears promising as a method of reducing the risk of seedling damage from seed-placed urea fertilizer, thus increasing the rate of urea-n that can be safely placed with the seed. Key words: Urease inhibitor, seedling toxicity, ammonia Grant, C. A. et Bailey, L. D Effet de la localisation dans la ligne de semis de l urée en présence de l inhibiteur d uréase NBPT sur le taux de levée et sur le rendement en grain de l orge. Can. J. Plant Sci. 79: L endommagement des plantules dû à un excès d urée engrais dans la ligne de semis peut constituer un gros problème dans les systèmes à semis et fertilisation en un seul passage. Des études au champ ont été réalisées durant 3 ans sur un loam argileux et sur un loam sableux fin avec pour objet d évaluer l impact de la localisation dans la ligne de semis d urée engrais avec ou sans l inhibiteur d uréase NBPT (triamide n-(n-butyl) thiophosphorique) sur la densité de peuplement et sur la croissance de l orge. Des endommagements des plantules, révélés par la diminution de la densité de peuplement, étaient observés dans les deux types de sol, même à des taux de fumure N ne dépassant pas 40 kg N ha 1. L ajout de NBPT à l urée produisait un accroissement de la densité de peuplement à des niveaux de fumure N qui, sans cela, causaient des endommagements. Le rendement en matière sèche à l épiaison n était généralement pas influencé par l urée ni par le NBPT, mais l utilisation de l inhibiteur donnait lieu à un accroissement du rendement grainier à 4 des 5 années-emplacements. Cette molécule offre un moyen prometteur de réduire les risques d endommagement des plantules associés à la localisation de l urée engrais dans la ligne du semis et, par voie de conséquence, d accroître la dose de l engrais que l on peut sans danger placer au voisinage immédiat de la semence. Urea is a popular form of N fertilizer due to its high N analysis, ease of handling and storage, and relatively low cost. Urea is readily soluble in water and can be used in the formulation of urea ammonium nitrate (UAN) and compound fertilizers. Seed-placement of fertilizer is a popular option for producers because it allows seeding and fertilizer application in a single operation, reducing labour and operational costs. Seed-placement of fertilizer reduces soil disturbance, as compared with incorporated or banded applications and reduces equipment costs and draft requirements as compared to side-banded applications. As a specialized form of fertilizer banding, seed-placement of fertilizer N is comparable to any other in-soil fertilizer band in terms of reduced volatilization and improved fertilizer use efficiency (Manitoba Agriculture 1999). Seed-placed urea-containing fertilizers, however, can frequently lead to severe seedling damage when applied at rates required to optimize crop yield (Gasser 1964; Bremner 1995). Seedling damage occurs when urea hydrolyses to ammonia (NH 3 ) in a reaction catalyzed by the enzyme urease Mots clés: Inhibiteur d uréase, toxicité envers les plantules, ammoniac 491 (Bremner and Krogmeier 1988; Bremner 1995). The NH 3 is in an equilibrium reaction with ammonium (NH 4 + ) in the soil solution. The more rapidly the urea hydrolyses, the higher the concentration of NH 4 + and NH 3 present in the soil solution. Seedling damage from seed-placed fertilizers is directly related to the concentration of NH 3 /NH 4 + in contact with the germinating seedling. Since both NH 4 + and NH 3 are present, seedling damage can occur both through a salt effect, due to an increase in the osmotic potential of the soil solution that desiccates the plant, and through direct ammonium toxicity (Olson and Kurtz 1982). Damage will increase with decreasing moisture levels during germination; therefore, drying conditions after seeding will increase damage, while significant rainfall after seeding will decrease damage (Tisdale et al. 1985). Damage tends to be Abbreviations: CEC, cation exchange capacity; NBPT, N-(n-butyl) thiophosphoric triamide; UAN, urea ammonium nitrate

2 492 CANADIAN JOURNAL OF PLANT SCIENCE Table 1. Chemical characteristics of soils at the two sites from 1994 to 1996 Nitrate-nitrogen z Phosphorus ph Conductance 0 15 cm cm cm cm cm 0 15 cm (kg ha 1 ) (kg ha 1 ) (ds m 1 ) ± ± ± ± ± ± ± ± ± ± ± ± ± 1.2 ND y ND ND ± ± ± ± ± ± 3.8 ND ND ± ± ± ± ± ± ± ± ± ± ± ± ± ± 2.0 ND ND ± ± ± ± ± ± 3.0 ND ND z Nitrate-nitrogen measured at five depths in the soil profile. y ND, not determined. greater on coarse-textured soils or soils with low organic matter content because of their lower CEC and lower waterholding capacity (Tisdale et al. 1985). Increasing carbonate content and ph may increase the proportion of NH 3 present (Nelsen 1982) thereby increasing the subsequent NH 3 toxicity. Damage may be decreased by any action that decreases the concentration of urea in contact with the seed, such as increasing the width of the row over which the seed and fertilizer are spread, decreasing row spacing, or decreasing fertilizer rate. Seedling toxicity can be reduced by broadcasting or banding urea away from the seed. However, under reduced tillage systems, the soil disturbance associated with incorporation or fertilizer banding may not be desirable. Urease inhibitors also may reduce the toxicity of seed-placed urea (Bremner and Krogmeier 1988, 1989). Inhibiting urease activity slows the conversion of urea to NH 4 + and retains the N in the urea form for a longer period. The urease inhibitor reduces the concentration of NH 4 + present in the soil solution, thereby reducing the potential for seedling damage. Also, slowing the hydrolysis of urea allows more time for the urea to diffuse away from the seed, reducing the likelihood of seedling damage (Bremner and Krogmeier 1988, 1989). A number of urease inhibitors have been investigated and studies over the past decade indicate that NBPT may be an effective urease inhibitor currently available for use in the Great Plains region (Christianson et al. 1990; Bremner 1995). Studies using NBPT generally have focussed on its ability to reduce volatilization losses by slowing urea hydrolysis (Christianson et al. 1990, 1993) but several studies have evaluated the effect of NBPT on seedling toxicity. Bremner and Krogmeirer (1988, 1990) demonstrated that NBPT was able to reduce seedling toxicity from seed-placed urea in a range of crops. Xiaobin et al. (1995) reported that NBPT reduced seedling damage to wheat from seed-placed urea fertilizers in growth chamber studies. Schlegel (1991) determined in field studies conducted over three seasons on silt loam soils in west-central Kansas, that adding NBPT to UAN solutions was effective in reducing seedling toxicity in corn. The NBPT also reduced delays in emergence caused by NH 3 toxicity from the UAN solution. Since NBPT delays, rather than eliminates urea hydrolysis, its effectiveness on reducing seedling damage will depend on the diffusion characteristics of urea in the soil and on urease activity (Christianson et al. 1993). Information on the impact of NBPT on seedling emergence is limited, particularly for small grains grown under field conditions using reduced tillage. This study was therefore undertaken to determine the influence of NBPT on seedling emergence, growth and grain yield of barley grown under reduced tillage. MATERIALS AND METHODS The experiment was conducted during three growing seasons from 1994 to 1996, inclusive. Barley (Hordeum vulgare L. Bedford ) was grown at two Orthic Black Chernozem soils in western Manitoba, Canada, one a Newdale clay loam (loamy, mixed, frigid Typic Hapludoll; N) and one a Stockton fine sandy loam (coarse, loamy, mixed, frigid Typic Hapludoll; N). Selected chemical characteristics of the sites are shown in Table 1. Nitrate-N and phosphorus were extracted using sodium bicarbonate and concentrations measured using an autoanalyzer and an ICP, respectively. Soil ph and conductance were measured in deionized water (Carter 1993). Barley was sown at 100 kg ha 1 directly into standing wheat stubble to a depth of 4.0 cm between 25 April and 20 May with a 2-m-wide pneumatic plot seeder equipped with a SeedHawk 2-cm-wide hoe opener and packing system using a row spacing of 20 cm. The plot size was 2 m by 5 m. In the first season of the study, commercial monoammonium phosphate at 20 kg P ha 1 was applied as a pre-plant band while in the second and third seasons, the P was applied with the seed. Commercial urea fertilizer, alone or treated with NBPT was seed-placed at 0, 20, 40, 60, 80 and 100 kg N ha 1. Urea treated with NBPT at the recommended rate of 0.14% by weight was provided by Imperial Oil in 1994, Sherritt Fertilizers in 1995 and Veridian Fertilizers in Herbicides were applied as required according to provincial recommendations for the weed species present (Manitoba Agriculture 1997). Emergence counts were determined on two 1-m row lengths in each plot approximately 2 wk after seeding. Dry

3 GRANT AND BAILEY RESPONSE OF BARLEY TO UREA AND NBPT 493 Table 2. Effect of seed-placed urea, with (UI) and without (NI) the urease inhibitor NBPT, on stand density (plants m 2 ) of Bedford barley on a clay loam and fine sandy loam soil, from 1994 to 1996 N (kg ha 1 ) NI UI NI UI NI UI NI UI NI UI NI UI Contrasts N-linear NS N-quadratic NS NS NS NS UI vs. no UI UI N-linear NS NS UI N-quadratic NS NS NS NS NS 20 vs. 20 with UI NS NS NS NS NS 40 vs. 40 with UI NS NS NS NS NS 60 vs. 60 with UI NS NS NS vs. 80 with UI NS vs. 100 with UI SE matter yield was measured at early heading on two 1-m row lengths in each plot. Grain yield was measured by harvesting the centre five rows of each plot with a plot combine when all plots were fully mature (mid-august to mid- September). Samples were dried to a constant moisture at 60 C in a forced-air dryer and final weight was measured after weed seeds and volunteer wheat were removed from the samples. The experiment was arranged in a randomized complete block design with four replications of the 11 fertilizer treatments at each site. Statistical analysis was conducted using the GLM procedure of the SAS Institute, Inc (1985). As significant treatment interactions occurred with site and with year, data were analyzed separately by site and by site-year, using contrast analysis in the GLM procedure of SAS. Effects on stand density were analyzed with both log 10 transformed and nontransformed data, with similar results. Therefore, information is presented using the nontransformed data. Effects were considered significant at a P value of When effects showed significance between 0.05 and 0.1, the P values were listed in the tables and effects were mentioned in the text as tendencies in the data. If P values were greater than 0.1, the effects were considered non-significant. RESULTS Stand Density Stand density decreased with increasing N application in each site-year of the study, except for on the clay loam in 1996 when the effect was not significant (Table 2). The decrease in stand density with increasing N rate indicates seedling damage from the applied urea. Seedling damage was lower in site-years with wet conditions after seeding. In each site year, NBPT significantly reduced seedling damage. In 4 out of 6 site years, there was a urease inhibitor by N-linear interaction, relating to a greater reduction in seedling damage by use of NBPT at higher N levels. At 20 and 40 kg N ha 1, there was no significant improvement in stand density from using NBPT. As the rate of N application increased, seedling damage increased and the difference in stand density between N applied alone and N treated with NBPT increased. At the 60 kg N ha 1 rate, use of NBPT increased stand density significantly in 1 of the 6 site-years. At the 80 kg N ha 1 rate, significant difference occurred in 4 of 6 site-years. At the 100 kg N ha 1 rate, significant differences occurred in 5 out of 6 site years, with a tendency to increased stand densities (P < ) in the other site year. Therefore, the NBPT was consistently effective at reducing seedling injury and improving seedling emergence at N rates where damage from seed-placed urea occurred. Dry Matter Yield at Heading Reduction in stand density from excess seed-placed N did not necessarily influence dry matter yield at heading, indicating that the crop was able to recover to some extent from seedling damage (Table 3). On the clay loam soil, N application generally did not affect dry matter yield at heading, thus use of NBPT generally did not result in higher dry matter yield at the higher N rates. However, in 1994, at 100 kg N ha 1, dry matter yield was greater when NBPT was used than when the fertilizer was applied alone. In contrast, in 1995, there was a tendency (P < ) towards lower dry matter yield when the NBPT was used with the 100 kg N ha 1 rate of applied N. On the fine sandy loam soil, in 1994, when soil N levels were relatively high and seedling damage was significant (Tables 1 and 2), N application led to a reduction in dry matter yield where no NBPT was applied and use of NBPT with the urea increased dry matter yields. Dry matter yield with the inhibitor was significantly higher

4 494 CANADIAN JOURNAL OF PLANT SCIENCE Table 3. Effect of seed-placed urea, with (UI) and without (NI) the urease inhibitor NBPT, on dry matter yield (g m 1 ) at heading of Bedford barley on a clay loam and fine sandy loam soil, from 1994 to 1996 N (kg ha 1 ) NI UI NI UI NI UI NI UI NI UI NI UI Contrasts N-linear NS NS NS N-quadratic NS NS NS NS NS UI vs. no UI NS NS NS NS NS UI N-linear NS NS NS NS NS NS UI N-quadratic NS NS NS NS vs. 20 with UI NS NS NS NS NS NS 40 vs. 40 with UI NS NS NS NS NS 60 vs. 60 with UI NS NS NS NS NS vs. 80 with UI NS NS NS NS NS 100 vs. 100 with UI NS NS NS SE than without NBPT at the 40 and 100 kg N ha 1 rates. In 1995, at the fine sandy loam site, when wet conditions after seeding reduced seedling damage, dry matter yield increased with N application and there was a tendency (P < ) toward a UI by N-quadratic interaction. The interaction was related to higher dry matter yield with 80 kg N ha 1 when urea was applied alone than when NBPT was used. In 1996, soil N levels were very low and dry matter yield tended (P < ) to increase with N application. A UI by N-quadratic interaction occurred, related to higher dry matter yield with NBPT at the 60 kg N ha 1 rate (P < ). The contradictory results noted indicate that dry matter yield at flowering was not closely related to early-season damage and showed wide variation in its response to both N and NBPT. Grain Yield As with stand density, grain yield was influenced by both N applications and use of NBPT in most site-years. Grain yield was increased by use of NBPT in 4 of 6 site-years (Table 4). Significant effects were not observed on the clay loam soil in 1996, when blackbird damage prior to harvest destroyed many plots, greatly increasing the variability and reducing the reliability of the final yield determination. Effects were also not significant on the fine sandy loam soil in 1995, when damage from seed-placed N was not observed until the 100 kg N ha 1 rate. On the clay loam soil, in 1994, grain yield was higher when NBPT was used than in its absence at N rates between 40 and 80 kg N ha 1, although the level of significance at the 60 kg N ha 1 rate was only P < Similarly, on the clay loam soil in 1995, grain yield was higher with NBPT than in its absence at the 80 and 100 kg N ha 1 rates. On the fine sandy loam in 1994, grain yield was numerically higher with NBPT than in its absence at all N rates, but the difference was only significant at the 100 kg N ha 1 rate. Variability was high in this site-year. In 1995, there was a tendency (P < ) towards higher grain yield with NBPT than in its absence at the 100 kg N ha 1 rate. In 1996, grain yield was higher with NBPT than in its absence when evaluated across all rates, but the contrast was not significant at any specific rate. DISCUSSION Under field conditions, seedling damage in barley from seed-placed urea was consistently reduced by use of NBPT, leading to higher stand density. This supports the growth chamber results of Xiaobin et al. (1995) with wheat and the field observations of Schlegel (1991) in corn. While the impact of reduced stand density on dry matter yield at flowering was inconsistent, the final grain yield was generally reduced by damage from high rates of seed-placed N and increased by using NBPT to reduce this damage. Although damage would generally be expected to be greater on coarse-textured soils (Tisdale et al. 1985), seedling damage and stand reduction was observed on both the fine- and coarse-textured soils in this study. Seedling damage not only reduced stand density, but also reduced seedling vigour and delayed maturity. This may have decreased the ability of the crop to compete with weeds and volunteer cereals. Addition of the NBPT apparently increased the ability of the crop to compete with volunteer wheat by increasing stand density and early season vigour. High populations of volunteer wheat were visually apparent in the plots treated with high rates of N in the absence of NBPT, which would have decreased final barley yield due to competition. Similar effects would presumably occur due to competition with high populations of other weeds, such as wild oat or green foxtail and be accentuated in situations where effective weed control was lacking. Lack of effect on dry matter yield

5 GRANT AND BAILEY RESPONSE OF BARLEY TO UREA AND NBPT 495 Table 4. Effect of seed-placed urea, with (UI) and without (NI) the urease inhibitor NBPT, on grain yield (kg ha 1 ) of Bedford barley on a clay loam and fine sandy loam soil, from 1994 to 1996 N (kg ha 1 ) NI UI NI UI NI UI NI UI NI UI NI UI Contrasts N-linear NS NS NS N-quadratic NS NS NS NS NS NS UI vs. no UI NS NS UI N-linear NS NS NS NS UI N-quadratic NS NS NS NS NS 20 vs. 20 with UI NS NS NS NS NS NS 40 vs. 40 with UI NS NS NS NS NS 60 vs. 60 with UI NS NS NS NS NS 80 vs. 80 with UI NS NS NS NS 100 vs. 100 with UI NS NS NS SE may have been due in part to the inclusion of volunteer wheat biomass in the sample. Where seedling damage was severe, maturity of the crop was delayed by up to 1 2 wk. In a farming situation, this could result in downgrading of the crop and/or yield loss from weathering or frost damage. The amount of N that can be safely placed with the seed will vary substantially from year to year, depending on the environmental conditions occurring after seeding. During this study, damage generally became significant above 40 kg N ha 1 as environmental conditions after seeding did not generally promote severe drying. While use of NBPT led to increased safety of seed-placed urea, damage did occur in several site-years at the higher rates of N, even with use of NBPT. Therefore, the NBPT increases the amount of N that can be safely placed with the seed, but does not eliminate the risk of damage at very high N application rates. Use of NBPT is an option for reducing damage from seed-placed N. Other alternatives would include using sources of seedplaced N, such as ammonium nitrate (Diebert 1986) or urea ammonium nitrate, which may be less damaging to the emerging seedling. Reducing the concentration of N in the row by spreading the fertilizer with a sweep or using wider opener systems (Deibert 1986) or by physically separating the urea from the seed, by side-banding, mid-row banding or surface dribble-banding the N could allow for one-pass seed and fertilizer application with reduced risk of seedling damage. Use of NBPT with high rates of side-banded urea N or with surface urea applications may reduce risk of yield loss further. Evaluation of these options in comparison to use of NBPT is required to more fully assess their relative benefits. CONCLUSIONS The urease inhibitor NBPT was effective at reducing seedling damage from seed-placed urea when high rates of urea N fertilizer were applied. Where seedling damage did not occur, use of NBPT was not beneficial. Stand density was consistently higher when NBPT was added to high rates of seed-placed urea than when the urea was applied alone. Dry matter yield at heading frequently was not increased by use of NBPT, but grain yield was generally higher when NBPT was used than in its absence. Therefore, use of NBPT is a potential method of reducing the risk of seedling damage and increasing the amount of urea-n that can be seedplaced in a one-pass seeding operation. ACKNOWLEDGEMENTS Funding for this project was provided by Imperial Oil, Sherritt Fertilizers, Veridian, Agrium, Western Grains Research Foundation and the Matching Investment Initiative program of Agriculture and Agri-Food Canada. The technical assistance of Brian Hadley, Mike Svistovski, Les Mitchell and Kim Brown was greatly appreciated. Bremner, J. M Recent research on problems in the use of urea as a nitrogen fertilizer. Fert. Res. 42: Bremner, J. M. and Krogmeier, M. J Elimination of the adverse effects of urea fertilizer on seed germination, seedling growth, and early plant growth in soil. Proc. Natl. Acad. Sci. USA 85: Bremner, J. M. and Krogmeier, M. J Evidence that the adverse effect of urea fertilizer on seed germination in soil is due to ammonia formed through hydrolysis of urea by soil urease. Proc. Natl. Acad. Sci. USA 86: Bremner, J. M. and Krogmeier, M. J Effects of urease inhibitors on germination of seeds in soil. Commun. Soil Sci. Plant Anal. 21: Carter, M. R Soil sampling and methods of analysis. Canadian Society of Soil Science, Lewis Publishers, Boca Raton, FL. 823 pp. Christianson, C. B., Baethgen, W. E. Carmona, G. and Howard, R. G Microsite reactions of urea-nbtpt fertiliz-

6 496 CANADIAN JOURNAL OF PLANT SCIENCE er on the soil surface. Soil Biol. Biochem. 25: Christianson, C. B., Byrnes, B. H. and Carmona, G A comparison of the sulfur and oxygen analogs of phosphoric triamide urease inhibitors in reducing urea hydrolysis and ammonia volatilization. Fert. Res. 26: Deibert, E. J One-pass pneumatic fertilizing-seeding with various N sources and N rates. Pages in J. Havlin, ed. Proceedings of the Great Plains Soil Fertility Workshop. 4 5 March Denver, CO. Gasser, J. K. R Urea as a fertilizer. Soils Fert. 27: Manitoba Agriculture Guide to crop protection Manitoba Agriculture. Carman, MB. 254 pp. Manitoba Agriculture Soil fertility handbook. Manitoba Agriculture, Carman. MB. 46 pp. Nelsen, D. W Gaseous losses of nitrogen other than through denitrification. Pages in F. J. Stevenson, ed. Nitrogen in agricultural soils. Agronomy no. 22. ASA, Madison, WI. Olson, R. A. and Kurtz, L. T Crop nitrogen requirements, utilization and fertilization. Pages in F. J. Stevenson, ed. Nitrogen in agricultural soils. Agronomy no. 22. ASA, Madison, WI. SAS Institute, Inc SAS user s guide: Statistics. Version 5 ed. SAS Institute, Inc., Cary, NC. Schlegel, A. J Reduced ammonia phytotoxicity from UAN solution by the urease inhibitor N-(n-butyl) thiophosphoric triamide. J. Fert. Issues 8: Tisdale, S. L., Nelson, W. L., Beaton, J. D. and Havlin, J. L Soil fertility and fertilizers. 5th ed. Macmillan Publishing Company, New York, NY. 634 pp. Xiaobin, W., Jingfeng, X., Grant, C. A. and Bailey, L. D Effects of placement of urea with a urease inhibitor on seedling emergence, N uptake and dry matter yield of wheat. Can. J. Plant Sci. 75: