Biomass production and nitrogen accumulation and remobilisation by Miscanthus × giganteus as influenced by nitrogen stocks in belowground organs

The nitrogen (N) requirement of dedicated crops for bioenergy production is a particularly significant issue, since N fertilisers are energy-intensive to make and have environmental impacts on the local level (NO₃ leaching) and global level (N₂O gas emissions). Nitrogen nutrition of Miscanthus × giganteus aboveground organs is assumed to be dependent on N stocks in belowground organs, but the precise quantities involved are unknown. A kinetic study was carried out on the effect of harvest date (early harvest in October or late harvest in February) and nitrogen fertilisation (0 or 120 kg N ha⁻¹) on aboveground and belowground biomass production and N accumulation in established crops. Apparent N fluxes within the crop and their variability were also studied.Aboveground biomass varied between 24 and 28 t DM ha⁻¹ in early harvest treatments, and between 19 and 21 t DM ha⁻¹ in late harvest treatments. Nitrogen fertilisation had no effect on crop yield in late harvest treatments, but enhanced crop yield in early harvest treatments due to lower belowground biomass nitrogen content. Spring remobilisation, i.e. nitrogen flux from belowground to aboveground biomass, varied between 36 and 175 kg N ha⁻¹, due to the variability of initial belowground nitrogen stocks in the different treatments. Autumn remobilisation, i.e. nitrogen flux from aboveground to belowground organs, varied between 107 and 145 kg N ha⁻¹ in late harvest treatments, and between 39 and 93 kg N ha⁻¹ in early harvest treatments. Autumn remobilisation for a given harvest date was linked to aboveground nitrogen accumulation in the different treatments. Nitrogen accumulation in aboveground biomass was shown to be dependent firstly on initial belowground biomass nitrogen stocks and secondly on nitrogen uptake by the whole crop.The study demonstrated the key role of belowground nitrogen stocks on aboveground biomass nitrogen requirements. Early harvest depletes belowground nitrogen stocks and thus increases the need for nitrogen fertiliser.     

Indigenous legume fallows (indifallows) as an alternative soil fertility resource in smallholder maize cropping systems

Widening the range of organic nutrient resources, especially N sources, is a major challenge for improving crop productivity of smallholder farms in southern Africa. A study was conducted over three seasons to evaluate different species of indigenous legumes for their biomass productivity, N₂-fixation and residual effects on subsequent maize crops on nutrient-depleted fields belonging to smallholder farmers under contrasting rainfall zones in Zimbabwe. Under high rainfall (>800 mm yr⁻¹), 1-year indigenous legume fallows (indifallows), comprising mostly species of the genera Crotalaria, Indigofera and Tephrosia, yielded 8.6 t ha⁻¹ of biomass within 6 months, out-performing sunnhemp (Crotalaria juncea L.) green manure and grass (natural) fallows by 41% and 74%, respectively. A similar trend was observed under medium (650–750 mm yr⁻¹) rainfall in Chinyika, where the indifallow attained a biomass yield of 6.6 t ha⁻¹ compared with 2.2 t ha⁻¹ for natural fallows. Cumulatively, over two growing seasons, the indifallow treatment under high rainfall at Domboshawa produced biomass as high as 28 t ha⁻¹ compared with ∼7 t ha⁻¹ under natural fallow. The mean total N₂ fixed under indifallows ranged from 125 kg ha⁻¹ under soils exhibiting severe nutrient depletion in Chikwaka, to 205 kg ha⁻¹ at Domboshawa. Indifallow biomass accumulated up to 210 kg N ha⁻¹, eleven-fold higher than the N contained in corresponding natural fallow biomass at time of incorporation. Application of P to indifallows significantly increased both biomass productivity and N₂-fixation, translating into positive yield responses by subsequent maize. Differences in maize biomass productivity between indifallow and natural fallow treatments were already apparent at 2 weeks after maize emergence, with the former yielding significantly (P < 0.05) more maize biomass than the latter. The first maize crop following termination of 1-year indifallows yielded grain averaging 2.3 t ha⁻¹, significantly out-yielding 1-year natural fallows by >1 t ha⁻¹. In the second season, maize yields were consistently better under indifallows compared with natural fallows in terms of both grain and total biomass. The first maize crop following 2-year indifallows yielded ∼3 t ha⁻¹ of grain, significantly higher than the second maize crop after 1-year indifallows and natural fallows. The study demonstrated that indigenous legumes can generate N-rich biomass in sufficient quantities to make a significant influence on maize productivity for more than a single season. Maize yield gains under indifallow systems on low fertility sandy soils exceeded the yields attained with either mineral fertilizer alone or traditional green manure crop of sunnhemp.     

Lucerne management in an organic farming system under dry site conditions

Biological nitrogen fixation (BNF) as a result of the legumes–rhizobia symbioses is the main source of nitrogen in organic farming systems. Lucerne (Medicago sativa L.), used as green manure or as forage legume, is important on arable farms under dry site conditions. In a field experiment on organically managed agricultural fields, we examined the impacts of the utilisation system (harvested = forage production versus mulched = green manure) and the crop composition (pure lucerne crops versus lucerne–grass mixtures) on yield, biological nitrogen fixation (BNF), soil inorganic N content, N balance and water consumption of autumn-cultivated lucerne crops. The study was conducted at the University of Natural Resources and Applied Life Sciences, Vienna, in eastern Austria—a region characterized by pannonian site conditions (9.8 °C mean annual temperature, 545 mm average total precipitation) and stockless farming systems. Our results indicate that the utilisation system and the crop composition had no marked influence on above- and below-ground dry matter (DM) and N yield, soil inorganic N contents, BNF, or water use efficiency of lucerne. The level of symbiotically fixed N₂ in harvested lucerne was 89–125 kg N ha⁻¹ (27–33% Ndfa = nitrogen derived from atmosphere) in the first year and 161–175 kg N ha⁻¹ (47–49% Ndfa) in the second year of the study. The high soil inorganic N supply in the first year increased the N uptake from soil by lucerne and led to a reduced BNF. Under the dry and unfavourable conditions in both study years, the nitrogen release from the legume mulch was retarded and BNF in mulched lucerne was not reduced. Assuming low gaseous N losses by mulching (15–30 kg N ha⁻¹), the green manure system reached a positive N balance (+137 to +186 kg N ha⁻¹) for the subsequent crops because abundant residues remained on the field.     

Sweet sorghum productivity for biofuels under increased soil salinity and reduced irrigation

Sweet sorghum (Sorghum bicolor (L.) Moench.) is a drought-tolerant crop with high resistance to saline-alkaline soils, and sweet sorghum may serve as an alternative summer crop for biofuel production in areas where irrigation water is limited. A two-year study was conducted in Northern Greece to assess the productivity (biomass, juice, total sugar and theoretical ethanol yields) of four sweet sorghum cultivars (Sugar graze, M-81E, Urja and Topper-76-6), one grain sorghum cultivar (KN-300) and one grass sorghum cultivar (Susu) grown in intermediate (3.2 dS m⁻¹) or in high (6.9 dS m⁻¹) soil salinity with either low (120 mm) or intermediate (210 mm) irrigation water supply (supplemented with 142–261 mm of rainfall during growth). The soil salinity and irrigation water supply effects on the sorghum chlorophyll content index, photosystem II quantum yield, stomatal conductance and leaf K/Na ratio were also determined. The sorghum emergence averaged 75,083 plants ha⁻¹ and 59,917 plants ha⁻¹ in a soil salinity of 3.2 dS m⁻¹ and 6.9 dS m⁻¹, respectively. The most affected cultivar, as averaged across the two soil salinity levels, was the Susu grass sorghum emerging at 53,250 plants ha⁻¹, followed by the Topper-76-6 sweet sorghum emerging at 61,250 plants ha⁻¹. The leaf K/Na ratio decreased with decreasing irrigation water supply, in most cases, but it was not significantly affected by soil salinity. The dry biomass, juice and total sugar yields of sorghum that received 210 mm of irrigation water was 49–88% greater than the yields of sorghum that received the 120 mm of irrigation water. Sorghum plants grown in a soil salinity of 3.2 dS m⁻¹ produced 42–58% greater dry biomass, juice and total sugar yields than the yields of sorghum plants grown in a soil salinity of 6.9 dS m⁻¹. The greatest theoretical ethanol yield was produced by sweet sorghum plants grown in a soil salinity of 3.2 dS m⁻¹ with 210 mm of irrigation water (6130 L ha⁻¹, as averaged across cultivar), and the Urja and Sugar graze cultivars produced the most ethanol (7620 L ha⁻¹ and 6528 L ha⁻¹, respectively). Conclusively, sweet sorghum provided sufficient juice, total sugar and ethanol yields in fields with a soil salinity of 3.2 dS m⁻¹, even if the plants received 50–75% of the irrigation water typically applied to sorghum.     

Impact of organic manure and chemical fertilizers on artemisinin content and yield in Artemisia annua L

Artemisinin isolated from the aerial parts of Artemisia annua L. is a promising and potent antimalarial drug. It posses remarkable activity against both chloroquinine resistant as well as chloroquinine sensitive strains of Plasmodium falciparum. It is also useful in the treatment of cerebral malaria. The relatively low content of artemisinin in A. annua and unavailability of cost effective and viable synthetic protocol however, are major obstacles to the commercial production of the drug. The enhanced production of artemisinin is hence, highly desirable, which can be achieved by adequate and judicious supply of plant nutrients. The present experiment was therefore, designed to study the effect of organic manure (15 tonnes ha⁻¹) and chemical fertilizers (N₄₀₊₄₀, P₄₀, K₄₀, S₁₅₊₁₅ kg ha⁻¹; nitrogen, phosphorus, potassium and sulphur) on the accumulation of artemisinin and biomass in various plant parts through the developmental stages of A. annua L. Artemisinin yield (kg ha⁻¹) was also determined through the developmental stages of A. annua L. Artemisinin content and artemisinin yield of dried leaves were increased significantly at pre-flowering stage in the plants treated with NPKS (27.3% and 53.6%) and NPK (18.2% and 33.5%), respectively, when compared with control. Maximum dry yield of leaf ranging from 2596 to 3141 kg ha⁻¹ was observed at pre-flowering stage with various treatments.     

Improving crop yield and N uptake with long-term straw retention in two contrasting soil types

Retention and/or reincorporation of plant residues increases soil organic nitrogen (N) levels over the long-term is associated with increased crop yields. There is still uncertainty, however, about the interaction between crop residue (straw) retention and N fertilizer rates and sources. The objective of the study was to assess the influence of straw management (straw removed [S_Rem] and straw retained [S_Ret]), N fertilizer rate (0, 25, 50 and 75 kg N ha⁻¹) and N source (urea and polymer-coated urea [called ESN]) under conventional tillage on seed yield, straw yield, total N uptake in seed + straw and N balance sheet. Field experiments with barley monoculture (1983-1996), and wheat/barley-canola-triticale-pea rotation (1997-2009) were conducted on two contrasting soil types (Gray Luvisol [Typic Haplocryalf] loam soil at Breton; Black Chernozem [Albic Argicryoll] silty clay loam at Ellerslie) in north-central Alberta, Canada. On the average, S_Ret produced greater seed yield (by 205-220 kg ha⁻¹), straw yield (by 154-160 kg ha⁻¹) and total N uptake in seed + straw (by 5.2 kg N ha⁻¹) than S_Rem in almost all cases in both periods at Ellerslie, and only in the 1997-2009 period at Breton (by 102 kg seed ha⁻¹, 196 kg straw ha⁻¹ and by 3.7 kg N ha⁻¹) for both N sources. There was generally a considerable increase in seed yield, straw yield and total N uptake in seed + straw from applied N up to 75 kg N ha⁻¹ rate for both N sources at both sites and more so at Breton, but the response to applied N decreased with increasing N rate. The ESN was superior to urea in increasing seed yield (by 109 kg ha⁻¹), straw yield (by 80 kg ha⁻¹) and total N uptake in seed + straw (by 2.4 kg N ha⁻¹) in the 1983-1996 period at Breton (mainly at the 25 and 50 kg N ha⁻¹ rates). But, urea produced greater straw yield (by 95 kg ha⁻¹) and total N uptake in seed + straw (by 3.3 kg N ha⁻¹) than ESN in the 1983-1996 period at Ellerslie. The N balance sheets over the 1983-2009 study duration indicated large amounts of applied N unaccounted for (ranged from 740 to 1518 kg N ha⁻¹ at Breton and from 696 to 1334 kg N ha⁻¹ at Ellerslie), suggesting a great potential for N loss from the soil-plant system through denitrification and/or nitrate leaching, and from the soil mineral N pool by N immobilization. In conclusion, the findings suggest that long-term retention of crop residue may gradually improve soil productivity. The effectiveness of N source varied with soil type.     

Improving in-season nitrogen recommendations for maize using an active sensor

An active crop canopy reflectance sensor could be used to increase N-use efficiency in maize (Zea mays L.), if temporal and spatial variability in soil N availability and plant demand are adequately accounted for with an in-season N application. Our objective was to evaluate the success of using an active canopy sensor for developing maize N recommendations. This study was conducted in 21 farmers’ fields from 2007 to 2009, representing the maize production regions of east central and southeastern Pennsylvania, USA. Four blocks at each site included seven sidedress N rates (0–280 kg N ha⁻¹) and one at-planting N rate of 280 kg N ha⁻¹. Canopy reflectance in the 590 nm and 880 nm wavelengths, soil samples, chlorophyll meter (SPAD) measurements and above-ground biomass were collected at the 6th–7th-leaf growth stage (V6–V7). Relative amber normalized difference vegetative index (ANDVI_relative) and relative SPAD (SPAD_relative) were determined based on the relative measurements from the zero sidedress treatment to the 280 kg N ha⁻¹ at-planting treatment. Observations from the current study were compared to relationships between economic optimum N rate (EONR) and ANDVI_relative, presidedress NO₃ test (PSNT), or SPAD_relative that were developed from a previous study. These comparisons were based on an absolute mean difference (AMD) between observed EONR and the previously determined predicted relationships. The AMD for the relationship between EONR and ANDVI_relative in the current study was 46 kg N ha⁻¹. Neither the PSNT (AMD = 66 kg N ha⁻¹) nor the SPAD_relative (AMD = 72 kg N ha⁻¹) provided as good an indicator of EONR. When using all the observations from the two studies for the relationships between EONR and the various measurements, ANDVI_relative (R² = 0.65) provided a better estimate of EONR than PSNT (R² = 0.49) or SPAD_relative (not significant). Crop reflectance captured similar information as the PSNT and SPAD_relative, as reflected in strong relationships (R² > 0.60) among these variables. Crop canopy reflectance using an active sensor (i.e. ANDVI_relative) provided as good or better an indicator of EONR than PSNT or SPAD_relative, and provides an opportunity to easily adjust in-season N applications spatially.     

Dryland maize yields and water use efficiency in response to tillage/crop stubble and nutrient management practices in China

Rainfed crop production in northern China is constrained by low and variable rainfall. This study explored the effects of tillage/crop residue and nutrient management practices on maize (Zea mays L.) yield, water use efficiency (WUE), and N agronomic use efficiency (NAE) at Shouyang Dryland Farming Experimental Station in northern China during 2003–2008. The experiment was set-up using a split-plot design with 3 tillage/crop residue methods as main treatments: conventional, reduced (till with crop residue incorporated in fall but no-till in spring), and no-till (with crop residue mulching in fall). Sub-treatments were 3 NP fertilizer rates: 105–46, 179–78 and 210–92 kg N and P ha⁻¹. Maize grain yields were greatly influenced by the growing season rainfall and soil water contents at sowing. Mean grain yields over the 6-year period in response to tillage/crop residue treatments were 5604, 5347 and 5185 kg ha⁻¹, under reduced, no-till and conventional tillage, respectively. Grain yields under no-till, were generally higher (+19%) in dry years but lower (−7%) in wet years. Mean WUE was 13.7, 13.6 and 12.6 kg ha⁻¹ mm⁻¹ under reduced, no-till, and conventional tillage, respectively. The no-till treatment had 8–12% more water in the soil profiles than the conventional and reduced tillage treatments at sowing and harvest time. Grain yields, WUE and NAE were highest with the lowest NP fertilizer application rates (at 105 kg N and 46 kg P ha⁻¹) under reduced tillage, while yields and WUE tended to be higher with additional NP fertilizer rates under conventional tillage, however, there was no significant yield increase above the optimum fertilizer rate. In conclusion, maize grain yields, WUE and NAE were highest under reduced tillage at modest NP fertilizer application rates of 105 kg N and 46 kg P ha⁻¹. No-till increased soil water storage by 8–12% and improved WUE compared to conventional tillage, thus showing potentials for drought mitigation and economic use of fertilizers in drought-prone rainfed conditions in northern China.     

Simulating water use and N response of winter wheat in the irrigated floodplains of Northwest Uzbekistan

The crop-soil simulation model CropSyst was used to simulate growth, water- and N-uptakes of irrigated winter wheat (Triticum aestivum L. cv. Kupava) in Khorezm, in the dry lands of northwest Uzbekistan, Central Asia. CropSyst was calibrated using the findings of field experiments of 2005/06 and 2006/07 and validated for the 2007/08 season. A relative root mean squared error of 11% proved the accuracy between simulated and observed aboveground biomass and grain yield in 2007/08. Scenario analyses showed that N-leaching was high and ranged from 63 to 106 kg ha⁻¹ when irrigated between 749 and 869 mm during the first two cropping seasons. The simulated N-leaching was lowest and ranged from 7 to 15 kg ha⁻¹ when irrigation was only 148–395 mm during 2007/08. The considerable N losses during leaching and high N-uptakes by wheat together resulted in a negative N-balance even during applications of 180 and 240 kg ha⁻¹ of N-fertilizer. N scarcity in the N-balance was reduced with increasing N-fertilizer amounts and ranged from −29 to −153 kg N ha⁻¹ in 2005/06 and 2006/07. Despite a common shallow groundwater table in the region during some time of the year, scenario analysis revealed that only full irrigation water (580 mm) and N supply according to crop demand (180 kg ha⁻¹) guaranteed high grain yields, unless the water table is permanently shallow to overcome irrigation deficits. Limited irrigation and N application (40% and 55% of ‘optimal’, respectively) in combination with a groundwater table below 3 m resulted in a 55% yield decline. The CropSyst wheat model proved a robust tool for assessing the influence of water and N dynamics under conditions of varying irrigation and shallow groundwater tables. It thus has potential as a decision support not only in northwest Uzbekistan, but also in comparable regions of Central Asia.     

Spectral measurements of the total aerial N and biomass dry weight in maize using a quadrilateral-view optic

Heterogeneous crop stands require locally adapted nitrogen fertilizer application based on rapid and precise measurements of the local crop nitrogen status. In the present study, we validated a promising technique for the latter, namely a tractor-mounted field spectrometer with an oblique quadrilateral-view measuring optic, measuring solar radiation and canopy reflectance in four directions simultaneously. Dry matter yield (kg ha⁻¹), total N content (g N g⁻¹ dry matter) and total aerial N (aboveground N-uptake) (kg N ha⁻¹) in maize were determined in 10 m² calibration areas in 60 plots differing in their N treatment and seeding density three times in each of three years under field conditions. Results show that the sensor used can reliably determine total aerial N ranging from as little as 5 kg N to 150 kg N ha⁻¹ with R²-values ≥0.81 in 2002 and 2004, and with R²-values ranging from ≥0.57 to 0.84 in 2003. Dry matter yields from as low as 0.3–4.2 t ha⁻¹ could be determined with R²-values ranging from 0.67 to 0.91 in 2002 to 2004. The capacity to ascertain DM yield spectrally was drastically reduced in the higher yield range (>6 t ha⁻¹) probably due to decreased sensitivity of the spectral signal. N-contents were generally not well determined. Taken together there is a good potential to determine reliably differences in total aerial N or DM yield from the five leaf stages unfolded to the five node stage where typically nitrogen applications are carried out.     

Mineral fertilizer response and nutrient use efficiencies of East African highland banana (Musa spp., AAA-EAHB,cv. Kisansa)

Poor yields of East African highland bananas (Musa spp., AAA-EAHB) on smallholder farms have often been attributed to problems of poor soil fertility. We measured the effects of mineral fertilizers on crop performance at two sites over two to three crop cycles; Kawanda in central Uganda and Ntungamo in southwest Uganda. Fertilizers were applied at rates of 0N–50P–600K, 150N–50P–600K, 400N–0P–600K, 400N–50P–0K, 400N–50P–250K and 400N–50P–600K kg ha⁻¹ yr⁻¹. In addition 60Mg–6Zn–0.5Mo–1B kg ha⁻¹ yr⁻¹ was applied to all treatments, with the exception of the control plots which received no fertilizer. Fresh bunch mass and yield increased with successive cycles. Yield increases above the control ranged from 3.1 to 6.2 kg bunch⁻¹ (average bunch weight for all treatments 11.5 kg bunch⁻¹) and 2.2–11.2 Mg ha⁻¹ yr⁻¹ (average yield for all treatments 15.8 Mg ha⁻¹ yr⁻¹) at Kawanda, compared with 12.4–16.0 kg bunch⁻¹ (average bunch weight for all treatments 14.7 kg bunch⁻¹) and 7.0–29.5 Mg ha⁻¹ yr⁻¹ (average yield for all treatments 17.9 Mg ha⁻¹ yr⁻¹) at Ntungamo. The limiting nutrients at both sites were in the order K > P > N. Potassium, N and P foliar nutrient mass fractions were below previously established Diagnosis and Recommendation Integrated System (DRIS) norms, with the smallest K mass fractions observed in the best yielding plots at Ntungamo. Total nutrient uptakes (K > N > P) were higher at Ntungamo as compared with Kawanda, probably due to better soil moisture availability and root exploration of the soil. Average N, P and K conversion efficiencies for two crop cycles at both sites amounted to 49.2 kg finger DM kg⁻¹ N, 587 kg finger DM kg⁻¹ P and 10.8 kg finger DM kg⁻¹ K. Calibration results of the model QUEFTS using data from Ntungamo were reasonable (R² = 0.57, RMSE = 648 kg ha⁻¹). Using the measured soil chemical properties and yield data from an experiment at Mbarara in southwest Uganda, the calibrated QUEFTS model predicted yields well (R² = 0.68, RMSE = 562 kg ha⁻¹). We conclude that banana yields can be increased by use of mineral fertilizers, but fertilizer recovery efficiencies need to improve substantially before promoting wide-scale adoption.     

Effects of soil water content and nitrogen supply on the productivity of Miscanthus × giganteus Greef et Deu. in a Mediterranean environment

Miscanthus × giganteus is one of the most promising biomass crops for non-food utilisation. Taking into account its area of origin (Far East), its temperature and rainfall requirements are not well satisfied in Mediterranean climate. For this purpose, a research was carried out with the aim of studying the adaptation of the species to the Mediterranean environment, and at analysing its ecophysiological and productive response to different soil water and nitrogen conditions. A split plot experimental design with three levels of irrigation (I₁, I₂ and I₃ at 25%, 50% and 100% of maximum evapotranspiration (ETm), respectively) and three levels of nitrogen fertilisation (0 kg ha⁻¹: N₀, 60 kg ha⁻¹: N₁ and 120 kg ha⁻¹: N₂ of nitrogen) were studied. The crop showed a high yield potential under well-watered conditions (up to 27 t ha⁻¹ of dry matter). M. × giganteus, in Mediterranean environment showed a high yield potential even in very limited water availability conditions (more than 14 t ha⁻¹ with a 25% ETm restoration). A responsiveness to nitrogen supply, with great yield increases when water was not limiting, was exhibited. Water use efficiency (WUE) achieved the highest values in limited soil water availability (between 4.51 and 4.83 g l⁻¹), whilst in non-limiting water conditions it decreased down to 2.56 and 3.49 g l⁻¹ (in the second and third year of experiment, respectively). Nitrogen use efficiency (NUE) decreased with the increase of water distributed (from 190.5 g g⁻¹ of I₀ to 173.2 g g⁻¹ of I₂); in relation to N fertilisation it did not change between the N fertilised treatments (N₁ and N₂), being much higher in the unfertilised control (177.1 g g⁻¹). Radiation use efficiency (NUE) progressively declined with the reduction of the N fertiliser level (1.05, 0.96 and 0.86 g d.m. MJ⁻¹, in 1994, and 0.92, 0.91 and 0.69 g d.m. MJ⁻¹, in 1995, for N₂, N₁ and N₀, respectively).     

Chlorophyll meter-based nitrogen management of rice grown under alternate wetting and drying irrigation

Farmers have adopted alternate wetting and drying (AWD) irrigation to cope with water scarcity in rice production. This practice shifts rice land away from being continuously anaerobic to being partly aerobic, thus affecting nutrient availability to the rice plant, and requiring some adjustment in nutrient management. The use of a chlorophyll meter (also known as a SPAD meter) has been proven effective in increasing nitrogen-use efficiency (NUE) in continuously flooded (CF) rice, but its use has not been investigated under AWD irrigation. This study aimed at testing the hypotheses that (i) SPAD-based N management can be applied to AWD in the same way it is used in CF rice, and (ii) combining chlorophyll meter-based nitrogen management and AWD can enhance NUE, save water, and maintain high rice yield. Experiments were conducted in a split-plot design with four replications in the 2004 and 2005 dry seasons (DS) at IRRI. The main plots were three water treatments: CF, AWD that involved irrigation application when the soil dried to soil water potential at 15-cm depth of −20 kPa (AWD₋₂₀) and −80 kPa (AWD₋₈₀) in 2004, and AWD₋₁₀ and AWD₋₅₀ were used in 2005. The subplots were five N management treatments: zero N (N₀), 180 kg N ha⁻¹ in four splits (N₁₈₀), and three SPAD-based N-management treatments in which N was applied when the SPAD reading of the youngest fully extended leaf was less than or equaled 35 (N_SPAD35), 38 (N_SPAD38), and 41 (N_SPAD41). In 2005, N_SPAD32 was tested instead of N_SPAD41. A good correlation between leaf N content per unit leaf area and the SPAD reading was observed for all water treatments, suggesting that the SPAD reading can be used to estimate leaf N of rice grown under AWD in a way similar to that under CF. SPAD readings and leaf color chart (LCC) values also showed a good correlation. There were no water × nitrogen interactive effects on rice yield, water input, water productivity, and N-use efficiency. Rice yield in AWD₋₁₀ was similar to those of CF; yields of other AWD treatments were significantly lower than those of CF. AWD₋₁₀ reduced irrigation water input by 20% and significantly increased water productivity compared with CF. The apparent nitrogen recovery and agronomic N-use efficiency (ANUE) of AWD₋₁₀ and AWD₋₂₀ were similar to those of CF. The ANUE of N_SPAD38 and N_SPAD35 was consistently higher than that of N₁₈₀ in all water treatments. N_SPAD38 consistently gave yield similar to that of N₁₈₀ in all water treatments, while yield of N_SPAD35 about 90% of that of CF. We conclude that a combination of AWD₋₁₀ and SPAD-based N management, using critical value 38, can save irrigation water and N fertilizer while maintaining high yield as in CF conditions with fixed time and rate of nitrogen application of 180 kg ha⁻¹. Treatments AWD₋₂₀ and N_SPAD35 may be accepted by farmers when water and N fertilizer are scarce and costly. The findings also suggested LCC can also be a practical tool for N-fertilizer management of rice grown under AWD, but this needs further field validation.     

Effects of transition season management on soil N dynamics and system N balances in rice–wheat rotations of Nepal

In the low-input rice–wheat production systems of Nepal, the N nutrition of both crops is largely based on the supply from soil pools. Declining yield trends call for management interventions aiming at the avoidance of native soil N losses. A field study was conducted at two sites in the lowland and the upper mid-hills of Nepal with contrasting temperature regimes and durations of the dry-to-wet season transition period between the harvest of wheat and the transplanting of lowland rice. Technical options included the return of the straw of the preceding wheat crop, the cultivation of short-cycled crops during the transition season, and combinations of both. Dynamics of soil N_min, nitrate leaching, nitrous oxide emissions, and crop N uptake were studied throughout the year between 2004 and 2005 and partial N balances of the cropping systems were established. In the traditional system (bare fallow between wheat and rice) a large accumulation of soil nitrate N and its subsequent disappearance upon soil saturation occurred during the transition season. This nitrate loss was associated with nitrate leaching (6.3 and 12.8 kg ha⁻¹ at the low and high altitude sites, respectively) and peaks of nitrous oxide emissions (120 and 480 mg m⁻² h⁻¹ at the low and high altitude sites, respectively). Incorporation of wheat straw at 3 Mg ha⁻¹ and/or cultivation of a nitrate catch crop during the transition season significantly reduced the build up of soil nitrate and subsequent N losses at the low altitude site. At the high altitude site, cumulative grain yields increased from 2.35 Mg ha⁻¹ with bare fallow during the transition season to 3.44 Mg ha⁻¹ when wheat straw was incorporated. At the low altitude site, the cumulative yield significantly increased from 2.85 Mg ha⁻¹ (bare fallow) to between 3.63 and 6.63 Mg ha⁻¹, depending on the transition season option applied. Irrespective of the site and the land use option applied during the transition season, systems N balances remained largely negative, ranging from −37 to −84 kg N ha⁻¹. We conclude that despite reduced N losses and increased grain yields the proposed options need to be complemented with additional N inputs to sustain long-term productivity.     

Impact of nitrogen amount and timing on the potential of acrylamide formation in winter wheat (Triticum aestivum L.)

Acrylamide (AA), a potential human carcinogen, is formed in strongly heated carbohydrate-rich food as a part of the Maillard reaction. The amino acid asparagine (Asn) and reducing sugars are considered to be the main precursors for AA formation. In a 2-year field trial the impact of nitrogen (N) amount and timing on the content of AA precursors and the potential of AA formation in different winter wheat cultivars (cv.) were studied in association with respective grain yields and parameters of baking quality. Depending on year, cultivar and nitrogen treatment Asn contents ranged between 4 and 18 mg 100 g⁻¹ flour dry-matter (DM). Nitrogen treatments affecting crude protein contents in flours above 13% caused a considerable increase in free Asn. Nitrogen amounts of 220 kg N ha⁻¹ increased the contents of free Asn by between 130% and 270% depending on year and cultivar compared to the untreated controls. A close linear correlation between the content of free Asn and the potential of AA formation (2004: R² = 0.89, 2005: R² = 0.83) could be observed, whereas no correlation could be found between reducing sugars and the potential of AA formation, pointing to the importance of free Asn as the limiting and thus determining factor for the AA formation potential in wheat flours. To reach high crude protein contents and good sedimentation values demanded for breadstuffs, nitrogen amounts of at least 180 kg N ha⁻¹ were necessary. Nitrogen fertilization measures resulting in high crude protein contents above 13% enhanced the potential of AA formation by increasing the content of free Asn in flours. As long as demands from traders and producers for flour with high crude protein contents are not revised, lowering Asn contents and thus the potential for AA formation by application of N amounts below 180 kg N ha⁻¹ and abandoning the late application of N do not appear to be successful ways to reduce the risk of AA formation in breadstuffs.     

Radiation use efficiency,N accumulation and biomass production of high-yielding rice in aerobic culture

The concept of aerobic culture is to save water resource while maintaining high productivity in irrigated rice ecosystem. This study compared nitrogen (N) accumulation and radiation use efficiency (RUE) in the biomass production of rice crops in aerobic and flooded cultures. The total water input was 800–1300 mm and 1500–3500 mm in aerobic culture and flooded culture, respectively, and four high-yielding rice cultivars were grown with a high rate of N application (180 kg N ha⁻¹) at two sites (Tokyo and Osaka) in Japan in 2007 and 2008. The aboveground biomass and N accumulation at maturity were significantly higher in aerobic culture (17.2–18.5 t ha⁻¹ and 194–233  kg N ha⁻¹, respectively) than in flooded culture (14.7–15.8 t ha⁻¹ and 142–173 kg N ha⁻¹) except in Tokyo in 2007, where the surface soil moisture content frequently declined. The crop maintained higher N uptake in aerobic culture than in flooded culture, because in aerobic culture there was a higher N accumulation rate in the reproductive stage. RUE in aerobic culture was comparable to, or higher than, that in flooded culture (1.27–1.50 g MJ⁻¹ vs. 1.20–1.37 g MJ⁻¹), except in Tokyo in 2007 (1.30 g MJ⁻¹ vs. 1.37 g MJ⁻¹). These results suggest that higher biomass production in aerobic culture was attributable to greater N accumulation, leading to higher N concentration (N%) than in flooded culture. Cultivar differences in response to water regimes were thought to reflect differences in mainly (1) early vigor and RUE under temporary declines in soil moisture in aerobic culture and (2) the ability to maintain high N% in flooded culture.     

Forage soybean yield and quality response to water use

Forages could be used to diversify reduced and no-till dryland cropping systems from the traditional wheat (Triticum aestivum L.)-fallow system in the semiarid central Great Plains. Forages present an attractive alternative to grain and seed crops because of greater water use efficiency and less susceptibility to potentially devastating yield reductions due to severe water stress during critical growth stages. However, farmers need a simple tool to evaluate forage productivity under widely varying precipitation conditions. The objectives of this study were to (1) quantify the relationship between crop water use and dry matter (DM) yield for soybean (Glycine max L. Merrill), (2) evaluate changes in forage quality that occur as harvest date is delayed, and (3) determine the range and distribution of expected DM yields in the central Great Plains based on historical precipitation records. Forage soybean was grown under a line-source gradient irrigation system to impose a range of water availability conditions at Akron, CO. Dry matter production was linearly correlated with water use resulting in a production function slope of 21.2 kg ha⁻¹ mm⁻¹. The slope was much lower than previously reported for forage production functions for triticale (X Triticosecale Wittmack) and millet (Setaria italic L. Beauv.), and only slightly lower than slopes previously reported for corn (Zea mays L.) and pea (Pisum sativa L.) forage. Forage quality was relatively stable during the last four weeks of growth, with small declines in crude protein (CP) concentration. Values of CP concentration and relative feed value indicated that forage soybean was of sufficient quality to be used for dairy feed. A standard seed variety of maturity group VII was found to be similar (in both productivity and quality) to a variety designated as a forage type. The probability of obtaining a break-even yield of at least 4256 kg ha⁻¹ was 90% as determined from long-term precipitation records used with the production function. The average estimated DM yield was 5890 kg ha⁻¹ and ranged from 2437 to 9432 kg ha⁻¹. Regional estimates of mean forage soybean DM yield ranged from 4770 kg ha⁻¹ at Fort Morgan, CO to 6911 kg ha⁻¹ at Colby, KS. Forage soybean should be considered a viable alternative crop for dryland cropping systems in the central Great Plains.     

Effect of nitrogen rates on yield and quality of fennel (Foeniculum vulgare Mill.) accessions

Nitrogen rates and plant genotypes effects yield and quality of medicinal plants therefore, this experiment was conducted in order to determine the effects of nitrogen rates on fennel accessions quality and quantity. The experimental design was a split plot with nitrogen rate (0, 40, 80, 120 and 160 Kg N ha⁻¹) as main and accession (Isfahan, Tehran, Yazd and EU11486) as sub plots and replicated four times. The experiment was conducted at the Isfahan University of Technology Experimental Station, Isfahan, Iran during 2008-2009. Plant height, number of umbel per plant, 1000seed weight, number of seeds per umbel, seed yield, seed essential oil yield, seed and foliage essential oil contents and seed ash, protein and fiber contents were measured. Nitrogen fertilization increased all measured traits, but reduced ash content. On average, the highest seed and foliage essential contents and seed essential yield were produced at 160 kg per N ha⁻¹ and EU11486 was a superior cultivar for these traits. However, there was an interaction between N rate and accession on all traits. Isfahan (11.65 kg ha⁻¹), EU11486 (38.26 kg ha⁻¹), Tehran (15.32 kg ha⁻¹) and Yazd (22.06 kg ha⁻¹) produced the highest seed essential oil yield under application of 160, 80, 160 and 120 kg N ha⁻¹, respectively. Foliage of the accessions contained 0.45-0.91% essential oil and seeds of accessions contained 17.6-18.2% protein and 8.9-9.4% ash suggesting that foliage of fennel also is a good source of essential oil and seeds of fennel are good sources of protein and minerals. The results showed that N fertilization and accession can affect yield and quality of fennel and accessions responded differently to N fertilization rates, thus selection among the accessions and N rates for better fennel production is possible.     

Optimum nitrogen fertilization rates for second-year corn succeeding alfalfa under irrigation

The N contribution of alfalfa (Medicago sativa L.) to the succeeding corn (Zea mays L.) crop (FYC) is widely recognized. However, there is less information regarding the optimum N fertilization rates (ONR) for a second-year corn (SYC) following alfalfa. Thus, the objective of this study was to evaluate the response of SYC after alfalfa to N fertilization under irrigated semiarid conditions. Three field experiments of SYC following alfalfa were conducted between 2007 and 2009 in Northeast Spain. Treatments included the combination of six N rates applied to FYC (0, 50, 100, 150, 200, and 300 kg N ha⁻¹) with four N rates applied to SYC (0, 100, 200, and 300 kg N ha⁻¹). In one of the three fields, high SYC yields (16.8 Mg ha⁻¹) were obtained in plots that remained unfertilized during two consecutive years after alfalfa. On the other two fields, 81-100% of the maximum corn yields were obtained with application of 200 kg N ha⁻¹ to SYC. Results suggest that the typical N fertilizer rates applied to SYC after alfalfa in irrigated semiarid areas (300 kg N ha⁻¹) could be reduced by at least 100 kg N ha⁻¹, with small or no economic penalties and important reductions in N losses.     

Nitrogen applications modify seed and oil yields and fatty acid composition of winter mustard

Winter mustard (Brassica juncea L.) is not a common crop in the Southeastern United States. With increased interest in biodiesel production, there has been corresponding interest in mustard in this region. The objective of this study was to evaluate the effect of N fertilization (0, 50, 100, 150 kg N ha⁻¹) on productivity, oil content, and oil composition of winter mustard ‘Pacific Gold’ grown at three locations in Mississippi (Stoneville, and two locations at Verona, namely Verona silt loam (Verona-SL) and Verona clay (Verona-C)). Nitrogen did not affect oil content (percent oil). Seed and oil yields (kg ha⁻¹) increased with N application relative to the unfertilized control. At the Verona-C location, the concentration of oleic acid was higher in the 50 kg N ha⁻¹ treatment. At Stoneville, linolenic acid concentration was higher in the 150 kg N ha⁻¹ and lower in the 100 kg/N ha⁻¹ treatment, while it was not different in the other treatments. Overall, the yield of the fatty acids (FA) palmitic, palmitoleic, stearic, oleic, linoleic, linolenic, arachidic, eicosanoic, behenic, erucic, lignoceric, and nervonic acid increased with higher N rates (100 or 150 kg N/h). The highest yield of FA in the two Verona locations were achieved in the 100 kg N ha⁻¹, while greatest yield of FA at Stoneville was achieved in the highest N rate (150 kg N ha⁻¹). Means of mustard oil yields in our study in the higher fertility treatment ranged from 737 to 1094 kg ha⁻¹. This study demonstrated winter mustard production in Mississippi and possibly other areas in the Southeastern United States can be successful and could provide seed and oil yields comparable to yields from other production areas.