zero-N Treatment Research Articles

Decoupling between leaf nitrogen and radiation use efficiency in vegetative and early reproductive stages in high-yielding soybean.

Ontogenic changes in soybean radiation use efficiency (RUE) have been attributed to variation in specific leaf nitrogen (SLN) based only on data collected during seed filling. We evaluated this hypothesis using data on leaf area, absorbed radiation (ARAD), aboveground dry matter (ADM), and plant nitrogen (N) concentration collected during the entire crop season from seven field experiments conducted in a stress-free environment. Each experiment included a full-N treatment that received ample N fertilizer and a zero-N treatment that relied on N fixation and soil N mineralization. We estimated RUE based on changes in ADM between sampling times and associated ARAD, accounting for changes in biomass composition. The RUE and SLN exhibited different seasonal patterns: a bell-shaped pattern with a peak around the beginning of seed filling, and a convex pattern followed by an abrupt decline during late seed filling, respectively. Changes in SLN explained the decline in RUE during seed filling but failed to predict changes in RUE in earlier stages and underestimated the maximum RUE observed during pod setting. Comparison between observed and simulated RUE using a process-based crop simulation model revealed similar discrepancies. The decoupling between RUE and SLN during early crop stages suggests that leaf N is above that needed to maximize crop growth but may play a role in storing N that can be used in later reproductive stages to meet the large seed N demand associated with high-yielding crops.

Influence of different nitrogen sources on carbon and nitrogen metabolism and gene expression in tea plants (Camellia sinensis L.)

Nitrogen plays an important role in plant growth and development, with different nitrogen forms also having an impact on carbon/nitrogen metabolism. Unlike most plants, tea plants prefer ammonium over nitrate. In this paper, we focused on how different nitrogen sources regulate the carbon/nitrogen metabolism in tea plants. Tea seedlings of ‘Longjing 43’ were cultivated hydroponically in four different solutions (zero-nitrogen, only NH4+, only NO3− and mixed nitrogen (NH4+: NO3− = 1:1). We analyzed characteristic components of tea plants and related genes in carbon and nitrogen metabolism. Tea polyphenols and catechins representing carbon pool, increased when NO3− was supplied as the nitrogen source, and similar findings were recorded in the zero-nitrogen treatment. The expression of most catechins biosynthesis-related genes was up regulated under NO3− and zero-N treatment, that was associated with tea polyphenols and catechins changes. Compared with NO3− as the nitrogen source, NH4+ and mixed nitrogen treatments had a positive effect on the accumulation of amino acids, especially theanine, glutamate and arginine, and these components contribute to the freshness flavor of tea. The expression of ammonium-assimilation genes was also up-regulated with NH4+ supply. Under mixed nitrogen treatment, the ratio of total polyphenols to free amino acids (PP/AA) was between sole NH4+ and NO3− supply. Therefore, compared with single nitrogen source, carbon and nitrogen metabolism of tea plant was more balanced under mixed nitrogen treatment. The results suggested that NO3− as the nitrogen source promoted the biosynthesis of catechins enriching the carbon pool, whereas NH4+ supply was more conducive to nitrogen metabolism, indicating that different nitrogen sources could affect the carbon and nitrogen balance.

Effects of topsoil removal on nitrogen uptake, biomass accumulation, and yield formation in puddled-transplanted rice

• Topsoil removal reduced total N uptake, total dry biomass, and grain yield of rice. • Topsoil had the largest contribution to plant N uptake from midtillering to panicle initiation. • Topsoil removal had the largest effect on panicles m −2 among yield components. • Total dry biomass rather than harvest index was affected by topsoil removal. Rice nitrogen (N) uptake and yield formation depend on both applied N fertilizer and soil-derived N. In this study, we determined the effects of topsoil removal on the N uptake and yield formation of rice crop. Four rice varieties were grown in farmers’ fields in Wuxue County, Hubei Province, China in 2016–2018 under the treatments of topsoil removal (TR) and control (CK). The TR treatment was established by desurfacing soil at about half of the topsoil depth (11−15 cm). Experiments were conducted in three adjacent fields in the three years and 100 kg N ha −1 was applied in all plots except for zero-N treatment in 2018. Averaged across years, N treatments, and varieties, topsoil removal reduced total N uptake by 27.8 %. The period from midtillering to panicle initiation had the highest daily N uptake from topsoil compared with other growing periods. During this growing period, the percentage of N uptake from topsoil to plant N uptake ranged from 54.2 to 62.4 % with an average value of 56.4 % across both zero-N and N-applied treatments. On average, topsoil removal reduced grain yield by 16.7 % and total dry biomass by 17.6 %. Among yield components, panicles m −2 was mainly responsible for the yield reduction in TR. Furthermore, total dry biomass rather than harvest index explained the yield reduction in TR compared with CK. Our results suggest that topsoil provided substantial N to rice crop especially during the period from midtillering to panicle initiation for achieving higher grain yield through increased panicles m −2 and biomass production.

Insufficient nitrogen supply from symbiotic fixation reduces seasonal crop growth and nitrogen mobilization to seed in highly productive soybean crops.

Nitrogen (N) supply can limit the yields of soybean [Glycine max (L.) Merr.] in highly productive environments. To explore the physiological mechanisms underlying this limitation, seasonal changes in N dynamics, aboveground dry matter (ADM) accumulation, leaf area index (LAI) and fraction of absorbed radiation (fAPAR) were compared in crops relying only on biological N2 fixation and available soil N (zero‐N treatment) versus crops receiving N fertilizer (full‐N treatment). Experiments were conducted in seven high‐yield environments without water limitation, where crops received optimal management. In the zero‐N treatment, biological N2 fixation was not sufficient to meet the N demand of the growing crop from early in the season up to beginning of seed filling. As a result, crop LAI, growth, N accumulation, radiation‐use efficiency and fAPAR were consistently higher in the full‐N than in the zero‐N treatment, leading to improved seed set and yield. Similarly, plants in the full‐N treatment had heavier seeds with higher N concentration because of greater N mobilization from vegetative organs to seeds. Future yield gains in high‐yield soybean production systems will require an increase in biological N2 fixation, greater supply of N from soil or fertilizer, or alleviation of the trade‐off between these two sources of N in order to meet the plant demand.

Effect of long term fertilization management strategies on methane emissions and rice yield

Optimum fertilization is an efficient method to maintain rice yield and reduce N-losses. It is essential though to evaluate methane emissions from paddy fields, to further understand its impact on greenhouse gas budget. Therefore, a field experiment was conducted to investigate the effect of long-term optimum fertilization on CH4 emissions and rice yield. We collected data in the 7th and 8th year from a field experiment initiated in 2010. Four optimum fertilization strategies, reduced N-fertilizer and zero-P treatment (RNP, 200 kg N/ha), sulfur-coated urea combined with uncoated urea treatment (SCU, 200 kg N/ha), organic fertilizer combined chemical fertilizer treatment (OCN, 200 kg N/ha), organic fertilizer treatment (OF, 200 kg N/ha); and two controls, the farmers' N management (FN, 270 kg N/ha) and zero-N treatment (N0), were employed. The results showed the rice yields achieved for the optimum fertilization treatments (RNP, SCU, OCN, and OF) were similar with those for the FN. No significant differences in CH4 emissions among all treatments. Cumulative seasonal CH4 emissions were negatively correlated with grain yield (P < 0.05). In the RNP and SCU treatments, soil available K, mcrA gene and available P were the key variables affecting CH4 emissions; soil available K, available P and SOC contents were the key emissions factors for OCN and OF treatments. The SCU achieved the highest rice yield and lowest CH4 emission intensity among optimum fertilization treatments. These results suggest that long-term application of sulfur-coated urea combined with uncoated urea can maintain rice yield and reduce methane emissions from rice paddies.

Stimulated fine root growth benefits maize nutrient uptake under optimized nitrogen management

Optimized nitrogen (N) management reduces total N application without sacrificing cropyield. However, the underlining mechanisms have not been well investigated, especially lackingthe evidence from roots. Here we performed a two-year field experiment with maize grownunder zero-N, conventional N and optimized N applications and examined grain yield, N,phosphorous (P) and potassium (K) uptake and root length in diverse diameter classes. Resultsshowed that both conventional N and optimized N managements significantly increased plantnutrient contents and grain yield compared with zero-N treatment, but no obvious differencewas observed between the two N-fertilized treatments. Notably, the response of differentnutrients to N application was not synchronous temporally over the growth period, followingthe order of N first, P second and K last. Though N application generally had minor impact ontotal root length and root biomass, optimized N regime significantly increased fine root(diameter ≤ 0.2 mm) length compared with conventional N at the eighth leaf emerged stage. Thestimulated fine root growth under optimized N management is beneficial for adequate N uptakeduring the key growth stage, which determines subsequent PK acquisition and final crop yield.Our findings highlight the importance of fine roots in maize NPK uptake and a betterunderstanding of the response of fine roots to changes in N availability may therefore be criticalfor optimizing N input in maize farming system

Seed Yield and Biological Nitrogen Fixation for Historical Soybean Genotypes

Seed yield formation and biological nitrogen (N) fixation (BNF) were evaluated during the seed filling period (SFP) for historical soybean genotypes under contrasting N strategies. Overall, seed yield increased with the year of release, primarily associated with increments in the seed number component. The study showed that seed weight factor was maintained across decades regardless of the improvement in seed number. Nitrogen factor, evaluated as zero-N application via inorganic fertilizers versus high-N added, influenced seed yield via impacting seed weight factor. The latter plant trait improved with the high-N treatment, which was related to changes in the duration of the SFP rather than in the rate (seed biomass accumulation per day). The BNF parameter also reflected changes during the SFP related to the N treatment implemented, with high BNF (c.a. peak around 70-90%) under zero-N treatment, but still providing N via BNF at a lower rate (c.a. peak around 40-50%) for the high-N treatment. The latter demonstrated that the N fertilization reduced BNF by nearly 50% but did not completely inhibit this process. Thus, the zero-N plants counted on three sources of N to satisfy seed N demand: N-BNF, N-soil, and N-fertilizer. Lastly, the high-N treatment also positively impacted yields (+7 bu/a), which could potentially demonstrate a nitrogen limitation toward the end of the SFP for soybeans. Further testing will be performed during the next growing season to provide an improved yield and BNF characterization under different growing seasons (weather).

Effects of Short-term Tillage of a Long-term No-Till Land on Quantity and Quality of Organic C and N in Two Contrasting Soil Types

&lt;p&gt;Pre-seeding tillage of long-term no-till soil may alter soil quality by changing some properties, but the magnitude of change depends on soil type and climatic conditions. Effects of short-term (2 or 3 years) tillage (hereafter called reverse tillage [RT]) of land previously under long-term no-till (NT, 29 or 30 years), with straw management (straw removed [S&lt;sub&gt;Rem&lt;/sub&gt;] and straw retained [S&lt;sub&gt;Ret&lt;/sub&gt;]) and N fertilizer rate (0, 50 and 100 kg N ha&lt;sup&gt;-1 &lt;/sup&gt;in S&lt;sub&gt;Ret&lt;/sub&gt;, and 0 kg N ha&lt;sup&gt;-1 &lt;/sup&gt;in S&lt;sub&gt;Rem&lt;/sub&gt; plots) were determined in autumn 2011 on total organic C (TOC) and N (TON), light fraction organic C (LFOC) and N (LFON), and mineralizable N (N&lt;sub&gt;min&lt;/sub&gt;) in the 0-7.5, 7.5-15, or 15-20 cm soil layers at Breton (Gray Luvisol [Typic Cryoboralf] loam) and Ellerslie (Black Chernozem [Albic Argicryoll] loam), Alberta, Canada. Short-term RT following long-term NT had no significant negative effect on TOC and TON in soil at both sites, although these parameters tended to be slightly lower in the 0-7.5 cm soil layer with RT compared to NT. For the zero-N treatment, S&lt;sub&gt;Ret&lt;/sub&gt; had greater TOC and TON compared to S&lt;sub&gt;Rem&lt;/sub&gt; in both soil layers at both sites. On average, over both sites, TOC and TON in the 0-15 cm soil increased by 2.08 Mg C ha&lt;sup&gt;-1&lt;/sup&gt; and 0.216 Mg N ha&lt;sup&gt;-1&lt;/sup&gt;, respectively. Application of N fertilizer increased TOC and TON in both soil layers, up to the 50 kg N ha&lt;sup&gt;-1&lt;/sup&gt; rate at Breton (by 7.96 Mg C ha&lt;sup&gt;-1&lt;/sup&gt; and 0.702 Mg N ha&lt;sup&gt;-1&lt;/sup&gt; in the 0-15 cm soil) and up to the 100 kg N ha&lt;sup&gt;-1&lt;/sup&gt; rate at Ellerslie (by 5.11 Mg C ha&lt;sup&gt;-1&lt;/sup&gt; and 0.439 Mg N ha&lt;sup&gt;-1&lt;/sup&gt; in the 0-15 cm soil). In both RT and NT treatments, the effects of N rate on TOC and TON were similar for S&lt;sub&gt;Ret&lt;/sub&gt; and S&lt;sub&gt;Rem. &lt;/sub&gt;There was greater LFOC and LFON in the 7.5-15 cm soil layer with RT than NT at both sites. In the 0-15 cm soil layer, averaged over both sites, RT increased LFOC by 66 kg C ha&lt;sup&gt;-1&lt;/sup&gt; and LFON by 4.0 kg N ha&lt;sup&gt;-1&lt;/sup&gt;. In both 0-7.5 and 7.5-15 cm soil layers, LFOC and LFON increased with S&lt;sub&gt;Ret&lt;/sub&gt; compared to S&lt;sub&gt;Rem.&lt;/sub&gt; Averaged over both sites, the increase in LFOC and LFON in the 0-15 cm soil was 97 kg C ha&lt;sup&gt;-1&lt;/sup&gt; and 3.5 kg N ha&lt;sup&gt;-1&lt;/sup&gt;, respectively. Mass of LFOC and LFON increased dramatically in both soil layers with application of N fertilizer up to the 100 kg N ha&lt;sup&gt;-1&lt;/sup&gt; rate at both sites, with an average increase of 866 kg C ha&lt;sup&gt;-1&lt;/sup&gt; and 45.5 kg N ha&lt;sup&gt;-1&lt;/sup&gt;. In the zero-N treatment, LFOC and LFON increased with S&lt;sub&gt;Ret&lt;/sub&gt; compared to S&lt;sub&gt;Rem&lt;/sub&gt; under RT at Breton and under NT at Ellerslie. On average, tillage had no effect on N&lt;sub&gt;min&lt;/sub&gt; in soil, but S&lt;sub&gt;Ret&lt;/sub&gt; increased N&lt;sub&gt;min &lt;/sub&gt;in soil in both RT and NT, with an average increase of 4.8 kg N ha&lt;sup&gt;-1&lt;/sup&gt;. Application of N fertilizer increased N&lt;sub&gt;min&lt;/sub&gt; in the 0-20 cm soil up to 50 kg N ha&lt;sup&gt;-1&lt;/sup&gt; rate at Breton (by 13.7 kg N ha&lt;sup&gt;-1&lt;/sup&gt;) and up to 100 kg N ha&lt;sup&gt;-1&lt;/sup&gt; rate at Ellerslie (by 18.6 kg N ha&lt;sup&gt;-1&lt;/sup&gt;). In conclusion, RT had no effect on TOC, TON and N&lt;sub&gt;min&lt;/sub&gt; in soil, but LFOC and LFON increased with RT compared to NT in the 7.5-15 cm layer at one site. S&lt;sub&gt;Ret&lt;/sub&gt; and N fertilization usually had dramatic positive effects on TOC, TON, LFOC, LFON and N&lt;sub&gt;min&lt;/sub&gt; in soil compared to the corresponding treatments.&lt;/p&gt;

Accumulation and distribution of nitrogen in triticale varieties with different nitrogen utilization efficiencies under different nitrogen application levels

采用土培盆栽试验, 以小黑麦氮高效利用品种'Clxt82'、'PI429186'和氮低效利用品种'Clxt74'为材料, 研究0 (不施氮)、0.033 g(N)·kg^-1(低氮)和0.066 g(N)·kg^-1(正常氮)3个不同施氮水平下, 各生长时期氮素在器官间和器官内不同功能性氮素分配的特性。结果表明: 氮高效利用品种在氮素不足的条件下优势更明显, 抽穗期高效利用品种和低效利用品种间生物量的差异随施氮量的增加而减小, 在不施氮、低氮和正常供氮时'Clxt82'、'PI429186'地上部生物量分别为'Clxt74'的1.55倍、1.19倍、1.06倍和1.79倍、1.35倍、1.30倍。不同生育时期, 小黑麦氮积累量均随施氮量的增加而显著增加, 低氮和正常供氮处理, 在分蘖期、拔节期氮高效利用品种氮积累量均显著高于低效利用品种, 而在抽穗期差异则不大。随施氮量的增加, 氮素在叶片和穗部的分配比例减小, 在茎的分配比例增大; 分蘖期和拔节期, 氮高效利用品种茎中氮素分配比例小于低效利用品种, 叶片氮素分配比例则大于低效利用品种。抽穗期氮高效利用品种穗部氮素分配比例大于低效品种, 而叶部则相反。各生育时期各器官不同形态氮素含量总体上随施氮量的增加而增加。不施氮和低氮处理, 拔节期氮高效品种'Clxt82'、'PI429186'叶片营养性氮含量是低效品种'Clxt74'的1.31倍、1.76倍和1.12倍、1.35倍, 而结构性氮含量则是低效品种的86.12%、64.01%和80.82%、71.51%; 抽穗期氮高效品种'Clxt82'、'PI429186'叶片营养性氮含量是低效品种'Clxt74'的1.01倍、1.11倍和1.04倍、1.13倍, 结构性氮含量为低效品种'Clxt74'的74.99%、63.08%和75.78%、62.84%; 各时期品种间功能性氮素含量差异不大。低氮条件下氮高效利用品种通过降低结构性氮素含量、增加营养性氮素含量来满足氮素的利用和体内循环。

Nitrogen Application Rate and the Change in Carbohydrate Concentration in Leaves, Fruit, and Canes of Gold Kiwifruit

ABSTRACT Gold kiwifruit (Actinidia chinensis Planch. var. chinensis ‘Hort16A’) is an important crop for New Zealand. In this trial, all nutrients, except nitrogen (N), were applied at levels comparable to commercial practice. The control treatment received approximately 145 kg N/ha/y, a conservative rate of N application for kiwifruit. The zero-N treatment vines received all nutrients except N, and the high-N treatment received double the control levels of N. Carbohydrate concentrations in the leaves, fruit and canes of zero-N and high-N vines were determined periodically through the season for two years. There were lower total sugar concentrations in the leaves of the zero-N vines however total carbohydrate concentration content was higher in the zero-N fruit. Vegetative vigor was reduced in the zero-N vines when compared to the high-N vines. By reducing N, the partitioning of carbon to fruit appears favored. This effect may be due to modified sink strength under reduced N.

Nitrogen Application Rate and the Concentration of Other Macronutrients in the Fruit and Leaves of Gold Kiwifruit

ABSTRACT Gold kiwifruit (Actinidia chinensis Planch. var. chinensis ‘HORT16A’, marketed as ZESPRI™' ‘HORT16A’) is an important export crop for New Zealand. Nutrient management, including the application of nitrogen (N), for ‘HORT16A’ kiwifruit has mimicked strategies for the green (A. deliciosa ‘Hayward’) cultivar, however, physiological differences between Actinidia species necessitate the development of specific nutrient regimes for ‘HORT16A’ vines. In this trial, all nutrients, except N, were applied at levels comparable to commercial practice. The Control treatment received approximately 145 kg N ha/y, and was based on estimates of total N removed each year in the harvested fruit. The Zero-N treatment vines received all nutrients except N, and the High-N treatment received double the Control, approximately 295 kg N ha/y, for two consecutive seasons. The High-N treatment represents the upper limit of N application practices in commercial ‘HORT16A’ kiwifruit production. Zero-N fruit had higher calcium (Ca) and lower N concentration than High-N fruit in both seasons. Fruit potassium (K) and magnesium (Mg) concentrations were equivalent between these treatments in both seasons. Fruit phosphorus (P) concentration throughout the season was increased in the High-N treatment in both years. Fruit sizes were not different between treatments at final harvest in Year 1, being 130.5 ± 4.13 g, 125 ± 1.49 g, and 125 ± 3.29 g for the High, Control, and Zero-N vines, respectively. Larger fruit were harvested from the High-N vines (125 ± 4.69 g) in Year 2, than from either Control (113 ± 2.03 g) or Zero-N (118 ± 1.03 g) vines. Percent fruit dry matter (DM) content was higher in the Zero-N fruit (17.2 ± 0.06, 17.2 ± 0.06, and 16.8 ± 0.14 for Zero, Control, and High-N vines) at final harvest in Year 1. But values of fruit DM for all treatments were similar in Year 2 in spite of fruit size differences between treatments. Fruit DM for all treatments was slightly higher in Year 2 than in Year 1. Differences in fruit mineral concentration and fruit maturity at harvest may have contributed to increased incidence of low temperature breakdown (LTB) in the High-N fruit in Year 1. In Year 2, when fruit DM was higher in all treatments, yellow coloration was more developed. Total fruit N concentration was lower in Year 2 for all treatments than in Year 1, and LTB was minimal and not different between treatments. Leaves from Zero-N vines had reduced N in both years compared with Control and High-N vines. In contrast, leaf Ca and Mg concentrations were reduced in High N-vines, compared with values recorded in Zero-N vines in both seasons. Leaf K concentrations were comparable between treatments in both seasons. Leaf sulfur (S) concentration was reduced under the High-N treatment, and leaf P levels were increased under the High-N treatment in both years. These data demonstrate that N application influences the uptake and accumulation of other mineral elements in ‘HORT16A’ kiwifruit. In order to encourage desirable nutrient concentrations in both the fruit and leaves of ‘HORT16A’ kiwifruit, a reduction in N applied is suggested, and this would have little or no detrimental effect on vine performance over two seasons. Reduced N application will also reduce nitrate leaching which is estimated at 39 kg N ha/y under the Control treatment.

Large applications of fertilizer N at planting affects seed protein and oil concentration and yield in the Early Soybean Production System

An inverse relationship between soybean [ Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha −1 in 2002, 310 kg ha −1 in 2003, and 360 kg ha −1 in 2004. Eight cultivars ranging from Maturity Group II–IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all 3 years. Glyphosate herbicide was used in all 3 years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha −1 of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and non-irrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and non-irrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% non-irrigated and oil: 9.9% irrigated and 18.9% non-irrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation ( r = 0.45, P = 0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.

Influence of Large Amounts of Nitrogen on Nonirrigated and Irrigated Soybean

Nitrogen supplied by N2 fixation to soybean [Glycine max (L.) Merr.] may not be sufficient to maximize yield. Field studies were conducted in 2002, 2003, and 2004 on Sharkey clay soil (very‐fine, smectitic, thermic Chromic Epiaquert) at Stoneville, MS (33°26′ N lat). The objective was to determine the effect of high rates of N applied as a replacement for N2 fixation in nonirrigated and irrigated environments. Eight cultivars ranging from Maturity Group II to IV were planted on 17 Apr. 2002, 2 Apr. 2003, and 25 Mar. 2004. Not all cultivars were evaluated in all 3 yr. Glyphosate herbicide was used in all 3 yr and a non‐glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha−1 of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and nonirrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). In the PlusN treatment, granular NH4NO3 was surface applied at soybean emergence at rates of 290 kg ha−1 in 2002, 310 kg ha−1 in 2003, and 360 kg ha−1 in 2004. When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in significantly decreased ureide concentration (57.2 and 53.5% reduction) and significantly increased biomass accumulation (14.1 and 16.7%), N accumulation (12.8 and 28.1%), and seed yield (7.7 and 15.5%) for the irrigated and nonirrigated environments, respectively. The majority of the yield increase in each environment resulted from increased number of seed (9.5% irrigated and 16.2% nonirrigated). These results confirm the sensitivity of N2 fixation to drought and indicate that N2 fixation may limit yield of soybean grown in both irrigated and nonirrigated environments of the midsouthern USA, and that N2 fixation deficiencies occur before the beginning of processes that determine number of seed.

Diurnal variation of photosynthesis and photoinhibition in tea: effects of irradiance and nitrogen supply during growth in the field.

Diurnal changes in the rate of photosynthesis (A) of mature tea (Camellia sinensis (L.) O. Kuntze) bushes grown at high elevation in the field in Sri Lanka, were related to environmental conditions. Bushes were either unshaded, receiving 100% of incident photosynthetically active radiation (PAR), moderately shaded, (65% PAR) or heavily shaded (30% PAR). These treatments were combined with nitrogen fertilizer applications of 0, 360 and 720 kg ha(-1) year(-1). When recently fully expanded leaves were measured under the growing conditions on bright, clear days from dawn to dusk, A was greatest in the morning with increasing radiation between approximately 8 h and 10 h. Stomatal conductances (g(s)) and substomatal carbon dioxide concentrations (C(i)) were then large, leaf temperatures (T(L)) cool, and saturated water vapour deficits (VPD) small. However, as the irradiance, T(L) and VPD increased towards midday, A, g(s), photochemical quenching, and C(i) decreased, and non-photochemical quenching increased. In the late afternoon, irradiance, T(L) and VPD fell, but despite the relatively large increase in g(s) and C(i), A remained low; however, it recovered overnight. The zero-N treatment decreased total-N content of leaves by 50% and A by c. 20% (not significant). Leaves of unshaded plants receiving least N had significantly (P<0.05) smaller A and greater total sugar content than shaded but with abundant N, A and sugars did not differ between shade treatments. Analysis of the responses of A to environment in the morning compared to the afternoon, and of chlorophyll fluorescence, suggests that A was photoinhibited as a consequence of greatly increased PAR, whilst decreasing g(s) (related to changes in PAR, VPD and T(L)) caused C(i) to fall. End-product inhibition of A is not consistent with decreased C(i). Inhibition of A as a result of photoinhibition was minimized, but not eliminated, by abundant N. Interactions between factors regulating A in tea are discussed.

Effectiveness of alfalfa in reducing fertilizer N input for optimum forage yield, protein concentration, returns and energy performance of bromegrass-alfalfa mixtures

Grasses, when grown in association with legumes, may utilize some N fixed by the legumes resulting in improved forage dry matter and protein yield. Field experiments were conducted at Lacombe and Eckville, Alberta, Canada to determine the effectiveness of alfalfa (Medicago sativaLeyss) in reducing fertilizer N requirements for optimum forage dry matter yield (DMY), protein concentration (PC), net margins (returns above N fertilization and forage harvesting costs) and non-renewable energy performance of bromegrass (Bromus inermis Leyss)-alfalfa mixtures. Ammonium nitrate was applied in early spring of 1993 to 1995 at 0, 50, 100, 150 and 200 kg N ha−1 to five bromegrass-alfalfa compositions (pure bromegrass; 2:1, 1:1 and 1:2 ratio of bromegrass:alfalfa; and pure alfalfa) seeded in the summer of 1992. In the zero-N treatment, DMY was lowest in pure bromegrass stands, and increased substantially when alfalfa was grown in association with bromegrass. There was a marked increase in DMY from the application of N fertilizer in pure bromegrass stands, but the increase was much less in the mixed stands. There was a significant increase in PC in forage when bromegrass was grown in a mixture with alfalfa compared to bromegrass alone. Net margins were much greater from mixed stands than from pure bromegrass. In pure bromegrass stands, net margins increased with increasing N rates up to 200 kg N ha−1, but equivalent net margins were usually attained without fertilizer N in bromegrass-alfalfa mixtures as low as 2:1. Energy performance of pure bromegrass stands was substantially improved by including alfalfa in the stands, whereas application of N fertilizer caused a strong and steady decline in energy use efficiency. Our findings indicate that seeding alfalfa in mixed stands with bromegrass can generate savings in N fertilizer (for pure bromegrass stands) equivalent to about 100 kg N ha−1 or more, without any detrimental effect on forage yield, forage quality or net earnings. However, the short-lived nature of alfalfa in bromegrass-alfalfa mixtures remains a cautionary concern. Thus, producers should also adopt management practices that enhance longevity of alfalfa to maximize long-term benefits of using grass-legume mixtures.

Increasing organic C and N in soil under bromegrass with long-term N fertilization

Two field experiments were conducted on bromegrass (Bromus inermis Leyss.) on a thin Black Chernozem (Typic Boroll) at Crossfield, Alberta, Canada to determine the long-term effects of N fertilization on changes in concentration and mass of organic C and N in soil. In both experiments, bromegrass was harvested for hay each year. In the experiment where ammonium nitrate (AN) was applied annually at 0 to 336 kg N/ha for 27 consecutive years from 1968 to 1994, the concentration of total C in the 0–5 cm soil layer increased from 50.33 g/kg in the zero-N treatment to 61.64 g/kg with 56 kg N/ha and to 64.15 g/kg with the 112 kg N/ha rate. Total C in soil also increased in the 5–10, 10–15 and 15–30 cm layers but to a lesser extent. The mass of total C in the 0–30 cm soil layer was increased by 18.46 Mg/ha with 56 kg N/ha and by 23.38 Mg/ha with the 112 kg N/ha rate as compared to the zero-N treatment. Total N in soil followed a similar trend as total C. In the experiment which received four N sources [ammonium nitrate (AN), urea, calcium nitrate (CN) and ammonium sulphate (AS)] applied annually at 168 and 336 kg N/ha for 15 years from 1979 to 1993, the total C in soil was greater where N fertilizer was applied, but the increase in total C varied with N source. The concentration of total C in soil in the 0–5 cm layer tended to be greater with AN and AS than with CN, with the smallest increase from urea. The mass of total C in soil (average of four N sources) at the 168 kg N/ha rate was increased by 18.98 Mg/ha in 0–30 cm and by 43.48 Mg/ha in the 0–60 cm layer as compared to the check treatment. The concentration of total C in soil also increased in the deeper layers to a depth of 60 cm, but the increases were much smaller than in the 0–5 cm layer. The changes in total N in soil followed a similar pattern as total C. In conclusion, long-term annual additions of fertilizer N to bromegrass resulted in a marked increase in total C and N in soil and the increases were influenced by both rate and source of N fertilizer. The implications of these results are that grasslands can be managed to lessen the increase in atmospheric CO2 concentration, while also improving fertility (N-supplying capacity) and tilth of soil.

Effects of applied nitrogen on soil nitrate-nitrogen content after harvest of winter barley

Seven field trials were conducted on winter barley to define relationships between rate of applied N, the amount of nitrate-N present in the soil after harvest and the ratio of soil nitrate-N to grain yield. Applying N up to the economic optimum rate (estimated from yield and N rate data from individual trials) was associated with small increases in soil nitrate-N after harvest (the mean increase was 4 kg N ha−1). Where the optimum N rate was exceeded, soil nitrate-N levels increased to a greater extent. In every trial, the ratio of soil nitrate-N to yield showed a minimum at a fertilizer N rate below the economic optimum. However, the value of the ratio was always lower at the optimum N rate (mean value 6.0 kg N t−1) than at the zero-N treatment (mean value 8.9 kg N t−1) and the difference between the minimum value (mean 5.6 kg N t−1) and that found at the optimum N rate was small.

Nitrogen additions (NaNO 3 and NH 4NO 3) at Aber forest, Wales: I. Response of throughfall and soil water chemistry

Nitrogen was sprayed weekly onto the forest floor of a Sitka spruce stand for 2.5 years in a replicated block design experiment to investigate the impacts of chronic atmospheric nitrogen deposition, in both oxidised and reduced form, on these ecosystems. The nitrogen was applied as sodium nitrate at 35 or 75 kg N ha −1 year −1 and as ammonium nitrate at 35 kg N ha −1 year −1, and the response of the throughfall and soil water chemistry determined. The response to increased water availability was also determined in a zero-N treatment. Increased water availability resulted in decreased concentrations of ammonium and phosphate and increased hydrogen ion concentration in the throughfall above the height of the spray, indicating tree growth is limited by water at this site. No effect of increased nitrogen availability on throughfall or stemflow chemistry above that of the water response was observed. Ambient nitrogen inputs in throughfall plus stemflow were 17 kg N ha −1 year −1 of which 11 kg N ha −1 year −1 was leached. Retention capacity of additional nitrogen applied to the forest floor was found to differ for nitrate-N and ammonium-N. There was no retention capacity for incoming nitrate-N but 100% retention capacity for applied ammonium-N. Nitrate leaching losses increased in parallel with nitrate inputs and were independent of ammonium addition. There was no apparent transformation of ammonium to nitrate in the ammonium nitrate treatment. Total dissolved nitrogen losses were therefore lower in the ammonium nitrate 35 kg N ha −1 year −1 treatment relative to the sodium nitrate 35 kg N ha −1 year −1. As the soil exchange complex is dominated by aluminium, the increase in salt loading and lack of nitrate retention in both treatments was associated with increased soil water aluminium concentrations due to ion exchange between the incoming sodium or ammonium ions and aluminium on the soil exchange complex. No increase in soil water concentrations of any other cation, with exception of sodium in the sodium nitrate treatments, was observed. These findings suggest that any increase in nitrate deposition will result in increased nitrate and aluminium leaching at this site which can perhaps best be described as ‘nitrate saturated’. Elevated ammonium deposition will also result in increased aluminium leaching if accompanied by a mobile anion. More long term monitoring is required to evaluate these changes in soil water chemistry on tree vitality and the internal nitrogen cycle.

Soil and sweet cherry responses to irrigation with wastewater

Lambert sweet cherry (Prunus avium L.) established on Osoyoos loamy sand in 1983 was subjected to treatments involving all combinations of two types of irrigation (wellwater or municipal wastewater) and three rates of N fertilization (0, 68 and 136 g of N as NH4NO3 tree−1 yr−1), 1984–1987. The zero-N treatment was increased to 34 g N tree−1 in 1986–1987. Wastewater irrigation increased leaf N, P, K, B and Mn concentration, decreased leaf Mg and Ca and had few consistent effects on leaf Fe and Cu. Tree growth was increased after 2 yr but not after 5 yr by wastewater irrigation. Inadequate N and Zn nutrition appeared to limit long-term tree growth. After 5 yr, wastewater-irrigated soils had higher extractable P, K, and B and lower Ca and Mg than well-water-irrigated soils which had higher Ca and Mg to 0.9-m depth. Wastewater irrigation also increased extractable Na throughout the soil but insufficiently to adversely affect tree growth. Soil pH and electrical conductivity also increased during the experiment for both well- and wastewater-irrigated soils, but these increases did not cause alkalinity or salinity problems. Key words: Prunus avium L., wastewater irrigation, leaf nutrition, soil quality

THE EFFECT OF MUNICIPAL WASTEWATER IRRIGATION AND RATE OF N FERTILIZATION ON PETIOLE COMPOSITION, YIELD AND QUALITY OF OKANAGAN RIESLING GRAPES

Okanagan Riesling (Vitis sp.) vines, planted on a sandy soil in 1983, were trickle irrigated with municipal wastewater or well water and with each source of water there were 3 rates of N fertilization (0, 17 and 34 g N as NH4NO3 vine−1 y−1), 1984–1987. The zero-N treatment was increased to 8.5 g N vine−1 in 1986–1987. Wastewater-irrigated vines had increased petiole P, K and Ca but decreased Mg and in 2 of 3 yr decreased N in August. Increased rate of N fertilization increased petiole N at bloomtime but not in August, had minor effects on petiole P, K, Ca and Mg, and increased petiole Mn at highest N rates, especially (2 of 4 yr) in association with wastewater irrigation. Yield increased both for vines irrigated with wastewater and linearly with rate of applied N in 2 of the 3 fruiting years. Increased yield was not associated with increased petiole N concentration in August. Minor increases in soluble solids and juice pH of grapes at harvest were measured for wastewater-irrigated grapes in 2 yr. No horticultural limitations to the use of this wastewater to irrigate Okanagan Riesling grapes were observed over the 4-yr period.