Influence of applied nitrogen on potato part II: recovery and partitioning of applied nitrogen

Maximizing fertilizer nitrogen (N) uptake efficiency, while maintaining crop productivity may reduce potential nitrate contamination of groundwater. A two-year field investigation was conducted to evaluate the effects of applied N on fertilizer N uptake, uptake efficiency, and total fertilizer N recovery of potato (Solarium tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as₁₅N-depleted ammonium sulfate [(NH₄)₂SO₄] at rates 0, 56, and 112, kg N ha^-1 in a single application at planting or 112 and 168 kg N ha^-1 in split applications during the growing season. Fertilizer N uptake efficiency was relatively unaffected by the N treatments. Fertilizer N uptake efficiency for the whole crop at onset of senescence averaged 52 percent, while values calculated for tubers at harvest were 34 percent. An average of 27 percent of the applied N was present in the soil to a depth of 120 cm after harvest. Approximately 83 percent of this N was found in the 0–30 cm depth. Over 90 percent of the recovered soil N was in the organic form. In this investigation, crop fertilizer N uptake and fertilizer N recovery in soil averaged 63 percent and was largely unaffected by the rate or timing of fertilizer N applications.     

Response of four potato cultivars to rate and timing of nitrogen fertilizer

The release of three new potato (Solarium tuberosum L.) cultivars, Bannock Russet, Gem Russet, and Summit Russet, with unique plant growth characteristics, necessitates the development of appropriate N fertilizer recommendations. These three new cultivars, along with the standard cultivar, Russet Burbank, were treated with four N rates (0, 100, 200, and 300 kg N ha^?1) using two different application timing procedures (“early,” with two-thirds N applied preplant, and “late,” with one-third applied preplant). Measurements included total and U.S. No. 1 yields, petiole NO₃-N concentrations, and net returns derived from economic analysis using a processing-based contract. Each of the four cultivars showed a unique response to N application treatments. Bannock Russet achieved maximum yield and net returns with relatively small amounts of N fertilizer. It also showed no response to N application timing and had moderate NO₃-N sufficiency concentrations early in the season, that decreased markedly late in the season. Gem Russet N requirement for maximum yield was similar to that of Russet Burbank, but required a higher amount of N for maximum net returns. Gem Russet also showed no response to application timing and had NO₃-N sufficiency concentrations similar to or slightly higher than those of Russet Burbank. Summit Russet showed a strong trend for improved N use-efficiency when most of the N was applied early. On the other hand, analysis of net returns revealed a trend for greater profitability for Summit Russet when the majority of N was applied during tuber bulking. Petiole NO₃-N sufficiency concentrations for Summit Russet were generally higher than those for the other three cultivars. In comparison with some earlier studies with Russet Burbank, this research suggested lower optimal N rates and petiole NO₃-N sufficiency concentrations.     

Planting date and nitrogen management interactions in irrigated maize

It is becoming increasingly important to develop economically and environmentally sound nitrogen fertilizer management practices. The objective of this experiment was to determine the optimum N application time-crop planting time combination(s) at two N rates which would maximize N fertilizer use efficiency (NFUE) and maintain high grain yields of irrigated maize (Zea mays L.) in the western Corn Belt of the USA. Maize was planted three times at biweekly intervals during 1979–1981 on a Typic Argiudoll in eastern Nebraska. The ¹⁵N-depleted (NH₄)₂SO₄ was applied at rates of 90 or 180 kg N/ha in a band midway between maize rows at planting, or at the 4-, 8-, or 16-leaf growth stage during 1979–1980. Control plots (no N fertilizer applied) were maintained in each planting date. No N was applied during 1981 to allow study of residual treatment effects. Grain dry-matter yield and total N and fertilizer N (FN) contents of grain were determined, and NFUE was calculated as the fraction of FN in grain to applied FN.Very high N supply by the soil resulted in small effects of FN on yield and NFUE during the first year of treatment. According to the response surface analysis, greatest NFUE (52%) in concert with high grain yield (11.2 Mg/ha, the predicted maximum) would have been achieved by applying the low N rate at the 13- to 14-leaf growth stage to maize planted during the week before the average date of 10 May. Due to lower soil N supply the 2nd year of treatment, most corn with 90 kg N/ha did not produce near-maximum grain yields. However, yields within 10% of maximum were obtained when 90 kg N/ha was applied to the early planting at the 14- to 16-leaf stage, and NFUE was 67–71% with this treatment. Maximum NFUE with the application of 180 kg N/ha was only 44%. Recovery of residual FN in this silty clay loam soil was an important factor in the improvement of NFUE with delayed N applications the second year of treatment. In 1981, recovery of residual FN generally increased with a previous delay in N application time and was not greatly influenced by planting time. Early planting in combination with a modest rate of N applied very late during vegetative growth provided maximum recovery of FN in harvested grain, while maintaining high grain yields.     

Optimizing Phosphorus Fertilizer Management in Potato Production

Management of fertilizer phosphorus (P) is a critical component of potato production systems as potato has a relatively high P requirement and inefficiently uses soil P. Phosphorus promotes rapid canopy development, root cell division, tuber set, and starch synthesis. Adequate P is essential for optimizing tuber yield, solids content, nutritional quality, and resistance to some diseases. Although soil test P is the primary tool for assessing P fertilizer needs, in some areas petiole P analysis has been successfully utilized to guide in-season P applications. Potato has been shown in some studies to respond to fertilizer P at soil test levels considered very high for most other crops (100+ mg kg^?1 Bray P₁ or Mehlich I or III and 20+ mg kg^?1 sodium bicarbonate) especially on medium- to finer-textured soils. Even on high-testing soils, fertilizer P rates for top yields sometimes exceed 150 kg P₂O₅ ha^?1. In addition, many states/provinces continue to recommend half or more of the amount of P in the harvested portion of the crop irrespective of soil test P level. In most situations, few differences are expected among fertilizer P sources; however, high rates of diammonium phosphate (DAP) or urea-phosphate (UAP) should not be band-applied in contact or near the seed piece. Most research determined that fertilizer P was most efficiently used when band-applied at planting (e.g., 5 cm to each side of the seed piece); however, some western USA work on high-pH soils showed increased yields and petiole P levels with preplant broadcast applications. In-season applications with the irrigation water can be successful when the potato roots are sufficiently close to the soil surface; however, most research indicates that P applications are more effective when applied at planting or early in the season. Potato fertilizer phosphorus best management practices include: (1) apply the fertilizer P rate calibrated for local soils; (2) band-apply fertilizer P at least 5 cm from the seed piece, especially on very sandy soils or where DAP or UAP are used; (3) use petiole P tests to determine the need for in-season applications; (4) account for all P sources applied, including animal manures; and (5) utilize the best soil conservation practices to reduce P losses to surface waters.     

Influence of applied nitrogen on potato part I: Yield,quality, and Nitrogen uptake

Fertilizer nitrogen (N) may be managed to increase crop production and profitability while reducing nitrate contamination of groundwater. A two-year field investigation was conducted to evaluate the effects of applied N on tuber yield and quality, dry matter production and N uptake of potato (Solanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as ammonium sulfate [(NH₄)₂SO₄] at rates of 0, 56 and 112, kg N ha^?1 in a single application at planting or 112 and 168 kg N ha^?1 in split applications during the growing season. Total tuber yield generally increased with N applications up to 112 kg N ha^?1. Only one of the three experimental sites showed an increase in marketable tuber yield when 112 kg N ha^?1 was split evenly between planting and tuber initiation. Tuber specific gravity was not affected by N rate. Nitrogen rates of 112–168 kg N ha^?1 maximized dry matter production and plant tissue N concentration at onset of maturity and harvest. Tuber N concentration at harvest ranged from 13–17 g kg^?1 at two of the three locations. Values for the third experiment were 10–13 g N kg^?1. Whole crop N uptake at onset of senescence ranged from 45 to 225 kg N ha^?1 across all locations and treatments. An average of 67 percent of this N was found in tubers at harvest. Nitrogen fertilization exceeded N removal in harvested tubers by more than 50 kg N ha^?1 only for the 168 kg N ha^?1 treatment. These results indicate that acceptable tuber yield can be obtained with lower N rates than those currently used by most producers, with the potential for reducing net loss of N from the soil.     

Nitrogen and water effects on wheat yield in a Mediterranean-type climate. II. Fertilizer-use efficiency with labelled nitrogen

Under the Mediterranean farming conditions of Syria, rain-fed cropping predominates, but irrigation is increasing where water sources are available. In both rain-fed or irrigated systems, it is important to understand N use by crops and its behavior in the soil. In this paper, we report on nitrogen fertilizer-use efficiency (NFUE) by wheat (Triticum aestivum L.) under 1/3, 2/3 and full irrigation with ¹⁵N-labeled fertilizer at different application rates (0, 50, 100 and 150 kg N ha⁻¹) for two seasons with varying rainfall, i.e. 323 and 275 mm. NFUE values in the above-ground crop varied with measurement date, reaching a maximum before anthesis, and then, during the grain-filling period, either remaining constant under irrigation or decreasing, particularly under the rain-fed conditions. Irrigation increased the recovery of applied N in grain and straw at harvest from 10% in the wetter year to over 60% in the drier year. Nitrogen at 100 kg ha⁻¹ level increased recovery by >45% in the wetter year, while fertilizer recovery improved in the drier year only with enhanced water availability from irrigation. The Difference method (28–95%) for estimating N recovery diverged from the ¹⁵N Direct method (21–63%), emphasizing the need to examine both labeled, and unlabeled, N pools for interpretation of ¹⁵N studies. With irrigation, the crop removed significantly more fertilizer N than under rain-fed conditions, with less remaining in the soil; over 40% of the fertilizer N remained in the top 20-cm soil as organic N. Irrigation had no effect on the ¹⁵N recovery at depth, with no significant re-mineralization being detected. While NFUE is increased by higher rainfall and irrigation, fertilizer N losses under the Mediterranean climatic conditions of Syria are low. The apparent inefficiency induced by organic immobilization adds to total soil N, which can potentially be used by future crops.     

The Effect of Nitrogen Rate on Vine Kill,Tuber Skinning Injury,Tuber Yield and Size Distribution,and Tuber Nutrients and Phytonutrients in Two Potato Cultivars Grown for Early Potato Production

Early potatoes are typically produced using less nitrogen than a full season potato crop as high rates of nitrogen may delay tuber set and lead to excessive vine growth that is difficult to terminate prior to harvest. Bintje and Ciklamen potato cultivars were grown with preplant soil nitrogen levels of 34 to 38, 67, and 101 kg N ha^-1 in 2013 and 2014 near Paterson, Washington. Nitrogen rate had little impact on the number of tubers and stems per plant of both cultivars, but increasing nitrogen rate tended to increase leaf area of both cultivars. Vine desiccation of Bintje with diquat was less complete as nitrogen rate increased, while Ciklamen vine kill was reduced by higher nitrogen in 1 of 2 years. Tuber skinning injury, tuber weight loss, and tuber size distribution were not affected by nitrogen rate. Tuber skinning injury and tuber weight loss were reduced in both cultivars by harvesting at 4 weeks after initial vine kill compared to harvesting at 2 weeks after vine kill. Total tuber yield was lower for both Bintje and Ciklamen in 1 of 2 years at the 34 to 38 kg N ha^-1 rate. Tuber nitrogen and zinc levels tended to increase with increasing nitrogen rates, while most other nutrients, vitamin C, total phenolics, and antioxidant capacity showed little response. It appears that 67 kg N ha^-1 provides adequate nitrogen to produce a good tuber set and yield of small tubers while not producing excessive vine growth that may be more difficult to kill.     

The effect of various dynamics of N availability on winter pea–wheat intercrops: Crop growth,N partitioning and symbiotic N2 fixation

Cereal–legume intercrops are a promising way to combine high productivity and several ecological benefits in temperate agro-ecosystems. However, the proportion of each species in the mixture at harvest is highly variable. The aim of this study was to test whether the timing of small application of N fertilizer is an effective way of influencing the dynamic interactions between species during crop growth and affecting the percentage of each species in the biomass of the mixture without greatly disturbing N₂ fixation. The influence of timing of nitrogen fertilization in pea–wheat intercrops was studied as regards (i) the dynamics of crop growth, (ii) nitrogen acquisition of each species, (iii) the inhibition and recovery of symbiotic N₂ fixation (SNF) after N application and (iv) final performance (yield, % of wheat, grain protein content). This was assessed in winter pea–wheat (Pisum sativum L.–Triticum aestivum L.) intercrops in 2007 and 2008 at two locations in France. Whatever the stage of application, N fertilizer tended to increase wheat growth and to decrease pea growth. N fertilization (applied once at different dates from tillering to the end of stem elongation) delayed the decrease in the contribution of wheat to total biomass and maintained the competitive ability of wheat over pea for longer than in unfertilized intercrops. N acquisition dynamics and N sharing between the two species were modified by N fertilization and its timing. Crop conditions at the time of N application (growth and phenology of each species, and their proportions in the intercrop biomass) greatly influenced intercrop response to N fertilization. Partitioning between species of soil and fertilizer N was correlated with the proportion of wheat in the total intercrop biomass observed at the date of N application. Short-term inhibition of nitrates on SNF was shown during the few days after N application, whatever its date. SNF recovery after N applications was observed only until pea flowering, but was prematurely stopped by N fertilization after this stage. The effect of N fertilization on the amount of fixed N₂ at harvest was correlated with pea biomass. N fertilization affects N₂ fixation mainly by affecting crop growth rather than %Ndfa in pea–wheat intercrops. In conclusion, N fertilization could be used as a tool to enhance the contribution of wheat in the intercrop biomass but may reduce the amount of fixed N₂ in the intercrop by decreasing pea biomass.     

Management of plant residue for cassava (Manihot esculenta) production on an acid Ultisol in Southeastern Nigeria

A study consisting of two experiments was conducted in southeastern Nigeria during 1983 and 1984 to determine whether cassava (Manihot esculenta Crantz) production on sandy, acid Ultisols could be improved by residue management techniques. One experiment studied the effect of location of Eupatorium odoratum mulch on soil properties and crop growth. A second experiment studied the effect of tillage system and Eupatorium odoratum mulch on soil properties and crop growth. In both experiments mulch was applied at an annual rate of 12 t¹ ha⁻¹ (25% moisture content) in a split application at planting and 150 days after planting (DAP). No fertilizer was applied during the experiment.Concentration of mulch in the plant row resulted in values of within-row bulk density in the surface 0.10 m which were lower by 15% and 13% in 1983 and 1984, respectively. Tillage in combination with mulch reduced bulk density in the surface 0.10 m by an average of 10% and 9% in 1983 and 1984, respectively. No significant differences were found among other treatments. Soil chemical properties were unaffected by treatments in both experiments. Cassava tuber yield was unaffected by location of Eupatorium odoratum mulch. Both plowing and no-tillage when combined with mulch improved tuber yields. Cassava tuber yields of untilled plots were 16.8 and 12.7 t ha⁻¹ during 1983–1984, and 13.1 and 8.3 t ha⁻¹ during 1984–1985 in mulched and unmulched treatments, respectively. Tuber yields of tilled plots were 14.5 and 13.1 t ha⁻¹ during 1983–1984, and 11.3 and 6.9 t ha⁻¹ during 1984–1985 in mulched and unmulched treatments, respectively.     

Recovery of starter nitrogen-15 fertilizer with supplementarily applied ammonium nitrate on irrigated potato

Nitrogen contamination in ground water of potato (Solanum tuberosum L.) producing areas has indicated a need for improved management of N and water, particularly on sandy soil. Therefore, a field experiment was conducted with the objective of following the recovery and partitioning of starter¹⁵NH₄ and¹⁵NO₃ into potato plant tops and tubers in conjunction with additional supplementarily applied NH₄NO₄. Potato plants treated with starter¹⁵NH₄ or¹⁵NO₃ tended to increase the percent recovery of starter¹⁵N in tubers sampled from one growth time to the next to reach nearly 40% recovery toward the end of the season. Whole plants reached peak recovery of around 50% of the starter¹⁵N near mid-season. From then on, there was a trend for loss of starter¹⁵N by senescence, defoliation or translocation to the roots. The percent recovery of starter¹⁵N was significantly higher at final tuber harvest (not whole plants) for the treatment with starter¹⁵NH₄ at 112 kg ha^?1 combined with 112 kg ha^?1 of supplemental N as compared to the treatment with 112 kg ha^?1 of starter¹⁵NH₄ plus 224 kg ha^?1 of supplemental N. This difference may have been a result of isotope dilution. Early in June the accumulation of starter¹⁵NO₃ in whole plants was about five times as high as that from starter¹⁵NH₄. Later there was no difference in percent recovery of these two forms of N. The temporary delay in starter¹⁵NH₄ uptake was probably related to slow nitrification early in the season instead of preferential uptake of starter¹⁵NO₃.     

Nitrogen recovery and loss in a fertilized elephant grass pasture

Limited information is available regarding the recovery and loss of fertilizer nitrogen (N) applied to intensively managed tropical grass pastures. An experiment was carried out in Brazil to determine the fertilizer‐N recovery and ammonia volatilization loss in an elephant grass (Pennisetum purpureum, Schum.) pasture fertilized with 100 kg N ha^?1 as urea or ammonium sulphate, labelled with ¹⁵N, in late summer (LS) or in mid‐autumn (MA). Herbage mass was highest and litter mass was lowest in LS (P < 0·05). The N concentration of herbage was highest in autumn (P < 0·05) and the total N content in soil was lower in LS than in MA (P < 0·05), reflecting the high N uptake capacity of the grass. Proportionately higher ¹⁵N recovery in litter mass (P < 0·05) was observed in autumn (0·094) than in LS (0·0397) and the ¹⁵N recovery in herbage was 0·046 higher for ammonium sulphate‐fertilized pastures (P < 0·05; proportionately 0·243 for ammonium sulphate and 0·197 for urea). Around 0·60 of the fertilizer‐¹⁵N recovered was retained in soil and in non‐harvestable fractions of the plant. The NH₃ volatilization loss was higher in LS and most of the N loss occurred soon after fertilizer application. Urea and ammonium sulphate fertilizers were equally effective in sustaining herbage dry matter yield in the short term. However, the use of ammonium sulphate, rather than urea, would be preferable for LS applications when the objective is to reduce NH₃ volatilization losses.     

Effect of fertilization on crop responses and solute transport for rice crop in a sub-humid and sub-tropical region

In order to increase the efficacy of water and control the losses of fertilizer, it is necessary to assess the influence of level of fertilization on crop responses, movement and balance of water and solutes from fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization on crop responses and fertilizer solute transport in rice crop field in a sub-humid and sub-tropical region. Field experiment was conducted on rice crop (cultivar IR 36) during the years 2003, 2004, and 2005. The experiment included four fertilizer treatments comprising different levels of fertilizer application. The fertilizer treatments during the experiment were: F₁ = control with N:P₂O₅:K₂O as 0:0:0 kg ha^?1; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha^?1; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha^?1 and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha^?1. The results of the investigation revealed that the magnitudes of crop parameters such as grain yield, straw yield, and maximum leaf area index increased with increase in fertilizer application rate. The levels of fertilization had very little effect on water loss via deep percolation and water use by the crop. The levels of fertilization had considerable effect on N leaching loss and uptake of N whereas it had no significant impact on leaching loss of water-soluble phosphorus. This indicated that PO₄-P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. The results also revealed that increase in level of fertilization increased water use efficiency considerably by increased crop yield. From the observed data of nutrient use efficiency, crop yield and environmental pollution, the fertilization rate of N:P₂O₅:K₂O as 80:40:40 kg ha^?1 (F₂) was the most suitable fertilizer treatment for rice crop among studied treatments.     

Potato Stolon and Tuber Growth Influenced by Nitrogen Form

Abstract

Potato tuber initiation and its growth are key processes determining tuber yield, which are closely related to stolon growth, and are influenced by many factors including N nutrition. We investigated the influences of different forms of nitrogen (N) on stolon and tuber growth in sand culture with a nitrification inhibitor during 2010 – 2011, and using two potato cultivars. Plants supplied with NO₃-N (N as nitrate, NO₃^-) produced more and thicker stolons than those supplied with NH₄-N (N as ammonium, NH₄⁺) at tuber initiation stage. In the plants fed NO₃-N, the stolon tips swelled or formed tubers earlier and produced more tubers than in those fed with NH₄-N. However, no significant difference was observed among N forms in terms of tuber yield at harvest, this may have been because of the shoot growth rate at tuber initiation stage was lower in the plants fed NO₃-N. During the tuber bulking stage, the difference in shoot DWs among N forms began to decrease, and the shoot DW of plants fed NO₃-N was even heavier than those fed NH₄-N in some cases. The influence of N form on potato plant growth may therefore vary with the potato growth stage.     

Effect of fertilizer nitrogen source and cattle slurry on herbage production and nitrogen utilization

A field plot experiment was carried out on an established grassland sward from 1983–88 inclusive to examine the effects of time of application, chemical form of nitrogen (N) and cattle slurry dry matter (DM) content on yield and efficiency of N use. Four forms of fertilizer N (a semi-organic fertilizer, a combined 2.1:1 (w/w) semi-organic/calcium ammonium nitrate (CAN) fertilizer, CAN and urea, each supplying 300 kg N ha^?1 year^?1, were applied with or without unseparated or separated cattle slurry at 93 and 73 g kg^?1 DM respectively, both supplying approximately 150 kg N ha^?1 year^?1. All fertilizers and slurries were applied in three equal dressings (February/March, May/June and July/August). The efficiency of use of fertilizer and slurry N was evaluated by measuring DM yield, N uptake and apparent recovery of N in herbage at all harvests during each growing season. Fertilizer N application significantly increased (P<0.001) the mean yields of herbage at each harvest in all years. The form of fertilizer N had no significant effect (P>0.05) on first harvest and total herbage yields, nor on N uptakes by herbage at the first harvest in any year. The performance of urea and of CAN was more variable at the second and third harvests relative to that of the semi-organic or combined 2.2:1 (w/w) semi-organic/CAN sources which had similar efficiencies of N use. Lower DM production was associated with reduced uptake of N. Values for mean overall apparent recovery of N ranged from 57.9 ± 2.67% for the semi-organic fertilizer to 50.2±3.05% for CAN. Unseparated cattle slurry and separated cattle slurry produced similar herbage yields and N responses that were lower and more variable than with fertilizer N. The overall mean apparent recovery of N from unseparated cattle slurry was 25.5 ± 5.03% compared to 5.0 ± 4.74% for separated cattle slurry. Efficiency of N use was highest with spring applications and least with mid-season applications. Recoveries ranged from ?29% for separated cattle slurry applied in June 1984 to 56% for unseparated and separated cattle slurry applied in February 1988 and June 1987 respectively. No interactions were recorded between cattle slurry and fertilizer N in terms of DM production or N uptake by herbage. The results of this study support the use of a fertilizer N source, selected on a least-cost basis, in combination with slurry to promote spring herbage production. For subsequent production, N should be supplied in fertilizer form only. The use of urea is risky under low rainfall conditions. Mechanical separation did not improve the efficiency of use of slurry N.     

Response of russet norkotah clonal selections to nitrogen fertilization

The low vine vigor and high N requirement of Russet Norkotah may lead to N loss and groundwater contamination on coarse-textured soils. Recent clonal selections from Texas have produced strains that have larger and stronger vines, which may alter N requirements. This twoyear study examined the N use efficiency (NUE), yield, and quality of Russet Norkotah strain selections fertilized with different N levels on a Hubbard loamy sand in central Minnesota. The selections, Texas Norkotah Strain (TXNS) 112, TXNS 223, and TXNS 278 were grown with standard Russet Norkotah under irrigated conditions and received total N levels of 28, 112, 224, or 336 kg ha^-1. Total, marketable, and large (>340 g) tuber yields increased linearly (P>0.05) with rate of N application in 1998 but not in 1997. The genotype main effect was not significant for any of the tuber yield parameters measured based on fresh weight. Vine, tuber, and total dry biomass yields were 116%, 5.8%, and 13.2%, respectively, higher with the selections than Russet Norkotah. Harvest index (HI), or the proportion of total dry matter partitioned to tubers, was 7% greater for Russet Norkotah than the TXNS selections, reflecting the larger vine growth of the selections. The selections accumulated significantly higher N in the vines (0.113 kg kg^-1 N) than the standard clone (0.053 kg kg^-1 N) as N rate increased from 28 to 336 kg ha^-1, and the difference between the selections and the standard clone was larger at higher N rates than at lower N rates. Russet Norkotah partitioned 10% more N to tubers than did the TXNS selections, reflecting the difference in HI between the standard cultivar and its clones. Nitrogen recovered from fertilizer N applied in addition to the 28 kg ha^-1 starter N (NUE₂₈) averaged 36% and varied little with genotype, N rate, or cropping year. Biomass accumulation from similar N additions (AUE), however, was significantly higher for the selections than Russet Norkotah at 112 kg N ha^-1 in 1997 only. At low N rate (112 kg ha^-1), the selections had higher physiological use efficiency (PUE₂₈) (mean 45.9 g g¹) than Russet Norkotah (25.9 g g¹). Results from this study demonstrate that, although N recovery was similar for the four genotypes, the Texas Norkotah strains produced greater biomass than Russet Norkotah per kg N applied at low rate in 1997 and per kg of fertilizer N absorbed by the plant in both years. However, under the conditions of this study, higher biomass of the selections did not translate into a marketable yield advantage over the standard cultivar.     

Effect of seedpiece spacing and nitrogen fertilization on tuber yield, yield components, and nitrogen use efficiency parameters of two potato cultivars

The effect of seedpiece spacing on the efficiency of nitrogen (N) use by the potato crop is generally unknown. The objective of this experiment was to determine the effect of seedpiece spacing on tuber yield, yield components and N use efficiency parameters of two potato cultivars. Potato cultivars Atlantic and Shepody were grown at two rates of N fertilization (0 or 100 kg N ha^?1) and three seedpiece spacings (20, 30, or 40 cm) in 2000 to 2002. Wider seedpiece spacing increased mean tuber weight and the number of tubers per stem, but decreased total tuber yield. The higher tuber yield at the narrow seedpiece spacing was attributed to higher biomass production in combination with lower tuber specific gravity. Seedpiece spacing had no consistent effect on plant N accumulation, and therefore no consistent effect on N uptake efficiency (plant N accumulation /N supply from the soil plus fertilizer). However, a small increase in soil NO₃-N concentration in the hill at topkill at wider seedpiece spacing suggested plant N accumulation was slightly reduced at wider seedpiece spacing, but at a level that could not be detected from a plant-based measure of N accumulation. The reduced dry matter accumulation, but similar plant N accumulation, resulted in lower N use efficiency (plant dry matter accumulation / N supply) at wider seedpiece spacing. Wider seedpiece spacing also resulted in generally lower values of N utilization efficiency (plant dry matter accumulation / plant N accumulation) for the 40-cm compared with the 20- and 30-cm seedpiece spacings. Effects of seedpiece spacing on N use efficiency parameters were generally consistent across cultivars and fertilizer N rates. Wider seedpiece spacing did reduce the efficiency of N use by the potato crop; however, the magnitude of the effect was small under the conditions of this study.     

The response of a perennial ryegrass (Lolium perenne L.) seed crop to nitrogen fertilizer application in the absence of moisture stress

Responses of perennial ryegrass (Lolium perenne L.) to nitrogen (N) fertilizer application rates and timings vary widely, because water is often limiting. Yield response to N fertilizer application during autumn, late‐winter and spring, and the associated efficiency of use of these inputs, was assessed under conditions of non‐limiting soil moisture during two, one‐year lysimeter studies in Canterbury, New Zealand. There were significant (P < 0·05) increases in seed and herbage yields with increasing N fertilizer application. Seed yields differed with year; greatest yields were 300 g m^?2 in 1996 and 450 g m^?2 in 1997. Seed head numbers (r²=0·77), seeds head^?1 (r²=0·92) and herbage yield (r²=0·92) were the major determinants of seed yield in both years. Irrigation required to maintain the soil between 70% and 90% of field capacity was directly related (r²=0·94 and 0·99 in 1996 and 1997 respectively) to increases in herbage yield. Seed yield, seed quality (thousand seed weight and percentage of seed > 1·85 mg), efficiency of water use, efficiency of N fertilizer use and apparent N fertilizer recovery were greatest when N fertilizer was applied at a rate of 50 kg N ha^?1, 50 or 100 kg N ha^?1 and 150 kg N ha^?1 in autumn, late‐winter and spring respectively; further increases in spring N fertilizer stimulated vegetative growth, but not seed yield. As a management strategy, applying N fertilizer to match the N requirements of the crop during the reproductive stage of growth will result in high yields of high quality seed while minimizing environmental impact.     

Effects of Nitrogen Fertilizer Application Time on Dry Matter Accumulation and Yield of Chinese Potato Variety KX 13

Application time of nitrogen (N) fertilizer can significantly influence the yield and quality of potato tubers. The objective of this experiment was to assess the effects of N application time on dry matter accumulation in foliage and tubers, as well as on marketable tuber ratio, dry matter concentration, and specific gravity of the Chinese cultivar KX 13. The four treatments were as follows: all the 150 kg?N?ha^?1 applied at planting (T1); 100 kg N ha^?1 applied at planting and 50 kg N ha^?1 applied 1 week before tuber initiation (20 days after emergence, DAE) (T2); 100 kg N ha^?1 applied at planting and 50 kg N ha^?1 applied 1 week before tuber bulking stage (35 DAE) (T3); and 100 kg?N?ha^?1 applied at emergence and 50 kg N ha^?1 applied 1 week before tuber bulking stage (35 DAE) (T4). For all treatments, 90 kg P₂O₅ ha^?1 ((NH₄)₂HPO₄) and 150 kg K₂O ha^?1 (K₂SO₄) were applied at planting. Thirty tons per hectare of marketable tuber yield was achieved with T3, while 23 t ha^?1 marketable yield was achieved by applying all 150 kg N ha^?1 at planting (T1). Relative to treatment T1, T3 also significantly increased harvest index (HI) from 0.76 to 0.86 and marketable tuber ratio from 64.8% to 79.2%. Applying N at planting in conjunction with dressing at 20 DAE (T2) gave a high marketable tuber ratio (74%) and HI (0.86), but the lower total tuber yield led to a lower marketable tuber yield. Without N application at planting (T4), N dressing did not increase the yield and HI. Treatments with N dressing had no significant effect on specific gravity or dry matter concentration of tubers.     

Phosphorus efficiency in long-term (15 years) wheat–maize cropping systems with various soil and climate conditions

Long-term (over 15 years) winter wheat (Triticum aestivum L.)–maize (Zea mays L.) crop rotation experiments were conducted to investigate phosphorus (P) fertilizer utilization efficiency, including the physiological efficiency, recovery efficiency and the mass (the input–output) balance, at five sites across different soil types and climate zones in China. The five treatments used were control, N, NP, NK and NPK, representing various combinations of N, P and K fertilizer applications. Phosphorus fertilization increased average crop yield over 15 years and the increases were greater with wheat (206%) than maize (85%) across all five sites. The wheat yield also significantly increased over time for the NPK treatments at two sites (Xinjiang and Shanxi), but decreased at one site (Hunan). The P content in wheat was less than 3.00 g kg⁻¹ (and 2.10 g kg⁻¹ for maize) for the N and NK treatments with higher values for the Control, NP and NPK treatments. To produce 1 t of grain, crops require 4.2 kg P for wheat and 3.1 kg P for maize. The P physiological use efficiency was 214 kg grain kg⁻¹ P for wheat and 240 kg grain kg⁻¹ P for maize with over 62% of the P from P fertilizer. Applying P fertilizer at 60–80 kg P ha⁻¹ year⁻¹ could maintain 3–4 t ha⁻¹ yields for wheat and 5–6 t ha⁻¹ yields for maize for the five study sites across China. The P recovery efficiency and fertilizer use efficiency averaged 47% and 29%, respectively. For every 100 kg P ha⁻¹ year⁻¹ P surplus (amount of fertilizer applied in excess of crop removal), Olsen-P in soil was increased by 3.4 mg P kg⁻¹. Our study suggests that in order to achieve higher crop yields, the long-term P input–output balance, soil P supplying capacity and yield targets should be considered when making P fertilizer recommendations and developing strategies for intensively managed wheat–maize cropping systems.     

Response of Russet Burbank and Shepody potatoes to nitrogen fertilizer in two cropping systems

Russet Burbank and Shepody potatoes were grown with at-planting N fertilizer rates ranging from 0 to 270 kg ha^?1 during 1986 through 1989. Experiments were conducted each year following small grains and red clover. Total yields and tuber size were strongly increased by N on most sites where potatoes followed small grains. Specific gravities declined with increasing N rate. Total yields of Russet Burbank and Shepody were optimized at an average of 196 and 211 kg ha^?1 of N, respectively, following small grains. The effect of N fertilizer on yields was much less dramatic following red clover. Total yields averaged 88% of maximum with only 45 kg ha^?1 of N applied, compared to 77% of maximum for this N rate following small grains. Total yields for the two varieties were optimized at 126 and 136 kg ha^?1, respectively. U.S. #1 yields were generally not increased at N rates above 45 to 90 kg ha^?1 following red clover and tuber size was not increased at rates above 90 to 135 kg ha^?1. Based on these studies, the N fertilizer credit for red clover grown prior to potatoes can be up to 75 kg ha^?1. Maintenance of tuber quality necessitates conservative use of N fertilizer when potatoes are grown following legumes. The highest N rates tested suppressed total yields of Russet Burbank, a late-season, indeterminate variety, by approximately 9% averaged over cropping systems.