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.     

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.     

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.     

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.     

Modeling nutrient and water productivity of sorghum in smallholder farming systems in a semi-arid region of Ghana

The CERES-sorghum module of the Decision Support System for Agro-Technological Transfer (DSSAT) model was calibrated for sorghum (Sorghum bicolor (L.) Moench) using data from sorghum grown with adequate water and nitrogen and evaluated with data from several N rates trials in Navrongo, Ghana with an overall modified internal efficiency of 0.63. The use of mineral N fertilizer was found to be profitable with economically optimal rates of 40 and 80 kg N ha⁻¹ for more intensively managed homestead fields and less intensively managed bush fields respectively. Agronomic N use efficiency varied from 21 to 37 kg grain kg⁻¹ N for the homestead fields and from 15 to 49 kg grain kg⁻¹ N in the bush fields. Simulated grain yield for homestead fields at 40 kg N ha⁻¹ application was equal to yield for bush fields at 80 kg N ha⁻¹. Water use efficiency generally increased with increased mineral N rate and was greater for the homestead fields compared with the bush fields. Grain yield per unit of cumulative evapo-transpiration (simulated) was consistently higher compared with yield per unit of cumulative precipitation for the season, probably because of runoff and deep percolation. In the simulation experiment, grain yield variability was less with mineral N application and under higher soil fertility (organic matter) condition. Application of mineral N reduced variability in yield from a CV of 37 to 11% in the bush farm and from 17 to 7% in the homestead fields. The use of mineral fertilizer and encouraging practices that retain organic matter to the soil provide a more sustainable system for ensuring crop production and hence food security.     

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.     

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.     

Soil type,management history and current resource allocation: Three dimensions regulating variability in crop productivity on African smallholder farms

Soil fertility varies markedly within and between African smallholder farms, both as a consequence of inherent factors and differential management. Fields closest to homesteads (homefields) typically receive most nutrients and are more fertile than outlying fields (outfields), with implications for crop production and nutrient use efficiencies. Maize yields following application of 100 kg N ha⁻¹ and different rates and sources of P were assessed on homefields and outfields of smallholder farms in Zimbabwe. Soil organic carbon, available P and exchangeable bases were greater on the homefields than outfields. In each of three experimental seasons, maize yields in homefield control plots were greater than in the outfields of farms on a granitic sandy and a red-clay soil. Application of mineral N significantly increased maize yields on homefields in the first season (2.1–3.0 t ha⁻¹ on the clay soil and 1.0–1.5 t ha⁻¹ on the sandy soil) but the effects of N alone were not significant on the outfields due to other yield-limiting factors. Greatest yields of about 6 t ha⁻¹ were achieved on the clayey homefield with 100 kg N ha⁻¹ and 30 kg P ha⁻¹ applied as single super phosphate (SSP). Manure application gave greater yields (3–4 t ha⁻¹) than SSP (2–3 t ha⁻¹) in the sandy homefield and in the clayey outfield. Maize did not respond significantly to N, dolomitic lime, manure and P on the sandy outfield in the first and second seasons. In the third season, manure application (∼17 t manure ha⁻¹ year⁻¹) on the sandy outfield did result in a significant response in grain yields. Apparent P recovery in the first season was 55–65% when P was applied at 10 kg ha⁻¹ on the clayey homefield (SSP), clayey outfield (SSP and manure) and sandy homefield (manure) with apparent P recovery less than 40% when P was applied at 30 kg ha⁻¹. On the sandy outfield, P recovery was initially poor (<20%), but increased in the successive seasons with manure application. In a second experiment, less than 60 kg N ha⁻¹ was required to attain at least 90% of the maximum yields of 2–3 t ha⁻¹ on the sandy homefield and clayey outfield. N use efficiency varied from >50 kg grain kg⁻¹ N on the infields, to less than 5 kg grain kg⁻¹ N on the sandy outfields. Apparent N recovery efficiency by maize was greatest at small N application rates with P applied. We conclude that blanket fertilizer recommendations are of limited relevance for heterogeneous smallholder farms. Targeted application of mineral fertilizers and manure according to soil type and past management of fields is imperative for improving crop yields and nutrient use efficiencies.     

Lignin content and briquette quality of different fibre hemp plant types and energy sunflower

Fibre hemp and energy sunflower are potential energy crops for production of solid biomass as renewable energy. The current study estimated (i) the lignin content of fibre hemp and energy sunflower plants grown on different nitrogen treatments and (ii) the quality of the briquettes made from different plant types of fibre hemp (i.e. monoecious and dioecious), energy sunflower and the combination of fibre hemp and energy sunflower. The monoecious and dioecious fibre hemp cultivars (Chameleon, Finola and Santhica-27, USO-31, respectively) and the energy sunflower cultivar Wielkopolski were grown in the experimental field in 2008-2010 on Stagnic Luvisol soil. The plants were grown on N treatments of N0, mineral nitrogen (100 kg N ha⁻¹), cattle slurry (100 kg N ha⁻¹), sewage sludge (100 kg N ha⁻¹) and vetch (100 kg N ha⁻¹). Calorific values (16.6-17.4 MJ kg⁻¹) of briquettes pressed from different materials did not differ significantly and had relatively low sulphur (<0.05%) and chlorine content (0.03-0.37%). Briquettes with higher compactness were made from the sunflower and the dioecious hemp. Dioecious hemp had significantly higher lignin content. The dioecious hemp needs lower GDD values for maturating, its stems lignin content was higher than of monoecious hemp by harvest time and therefore this plant type is more suitable for briquetting in Nordic climatic conditions. Comparison of the different N treatments indicated that application of sewage sludge decreased the emergence and density of the fibre hemp plants and the lignin content per kg of DM.     

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.     

Mixing groundnut residues and rice straw to improve rice yield and N use efficiency

Groundnut as a pre-rice crop is usually harvested 1–2 months before rice transplanting. During this lag phase much of N in groundnut residues could be lost due to rapid N mineralization. Mixing of abundantly available rice straw with groundnut residues may be a means for reducing N and improve subsequent crop yields. The objectives of this experiment were to investigate the effect of mixing groundnut residues and rice straw in different proportions on (a) growth and yield of succeeding rice, (b) groundnut residue N use efficiency and (c) N lost (¹⁵N balance) from the plant–soil system and fate of residue N in soil fractions. The experiment consisted of six treatments: (i) control (no residues), (ii) NPK (at recommended rate, 38 kg N ha⁻¹), (iii) groundnut residues 5 Mg ha⁻¹ (120 kg N ha⁻¹), (iv) rice straw 5 Mg ha⁻¹ (25 kg N ha⁻¹), (v) 1:0.5 mixed (groundnut residues 5 Mg: rice straw 2.5 Mg ha⁻¹), and (vi) 1:1 mixed (groundnut residues 5 Mg: rice straw 5 Mg ha⁻¹). After rice transplanting, samples of the lowland rice cultivar KDML 105 were periodically collected to determine growth and nutrient uptake. At final harvest, dry weight, nutrient contents and ¹⁵N recovery of labeled groundnut residues were evaluated.     

Effect of winter cover crop species and planting methods on maize yield and N availability under irrigated Mediterranean conditions

Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha⁻¹ and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha⁻¹ at the control treatment, and this amount was reduced to 250 kg N ha⁻¹ in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha⁻¹ after barley in 2007 and by 1 Mg ha⁻¹ after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.     

Kernel number determination differs among maize hybrids in response to nitrogen

In maize, the effects of nitrogen (N) deficiencies on the determination of kernel number per plant (KNP) have been described only by changes in plant growth rate during the critical period for kernel set (PGRcp). We hypothesize that N availability affects KNP also through variations in biomass allocation to the ear, which determines a stable N concentration in this organ. Six maize hybrids of different breeding origin were evaluated in field experiments at two N levels (0 and 400 kg N ha⁻¹ applied). Traits included were KNP and per apical ear (KN_E1), and the allometric estimation of PGRcp, ear growth rate during the critical period (EGRcp), and N content and N concentration in different plant organs. We demonstrated that (i) N availability promoted differences among genotypes (G) in the response of EGRcp and KNP to PGRcp, (ii) variations in KN_E1 were explained by EGRcp (r² = 0.64) and by ear N content at silking + 12 d (r² = 0.64), and (iii) ear N concentration was a highly conservative trait (range between 10.47 and 15.98 mg N g biomass⁻¹) as compared to N concentration in vegetative tissues (range between 4.94 and 18.04 mg N g biomass⁻¹). Three response patterns were detected among hybrids, one for which the relationship between EGRcp and PGRcp did not vary between N levels and experiments, a second one for which N availability affected this relationship, and a third one for which the response was affected by the year (Y) effect. These results, together with the high correlation between EGRcp and ear N content (r² = 0.88), evidenced the importance of both photo-assimilate and N availability on EGRcp and KNP determination. Values of 1.5–2.3 g ear⁻¹ d⁻¹ during the critical period and 0.49–0.70 g of N ear⁻¹ at silking + 12 d were determined as thresholds for maximizing KN_E1, and both could be easily estimated by means of allometric models.     

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.     

Assessment of some major yield-limiting factors on maize production in a humid temperate environment

Despite the availability of modern hybrids and better agronomic practices, there existed large gaps between attainable yield of maize (Zea mays L.) grown with recommended practices and producers’ harvest yields in the humid temperate regions of eastern Canada. A field experiment was conducted for 3 years in Ottawa, Canada, to determine the most important management yield-limiting factor(s) on rainfed maize grain production. A package of recommended practices (RP) was composed with the recommended levels of nitrogen (N), phosphorus (P), potassium (K), micronutrients, chemical weed control, and plant population density (PPD). Each factor was modified from the RP, making a total of 11 treatments. Under the low occurrence of diseases or insects, weed infestation was the most important yield-limiting factor, which reduced grain yield by 27–38%. While lack of preplant N application (100 kg ha⁻¹) reduced yield by 10–22%, there was no yield increment with additional sidedressing N (50 kg N ha⁻¹). Grain yield was reduced by 8–13% with low PPD (60,000 plants ha⁻¹) in all years, whereas increasing PPD to 90,000 plants ha⁻¹ did not improve yield, compared with the RP. Withhold P application did not affect yield in all years, but yield was reduced by up to 13% in the absence of K, and by 10% and 12% without Zn or Mn, respectively, in 1 year. Our results indicated that lack of weed control (i.e. herbicide use) was the major yield-limiting factor followed by fertilizer N and PPD. The responses of grain yield to K, Zn, and Mn were site and/or year specific. Our study provided experimental data and an insight understanding of yield gap between genotype's yield potential achievable with recommended practices and yields with producers’ practices.     

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.     

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.     

Identification of traits to improve the nitrogen-use efficiency of wheat genotypes

Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N₂O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to analyze the genetic variability in N-use efficiency (grain dry matter (DM) yield per unit N available from soil and fertilizer; NUE) in winter wheat and identify traits for improved NUE for application in breeding. Fourteen UK and French cultivars and two French advanced breeding lines were tested in a 2 year/four site network comprising different locations in France and in the UK. Detailed growth analysis was conducted at anthesis and harvest in experiments including DM and N partitioning. Senescence of either the flag leaf or the whole leaf canopy was assessed from a visual score every 3-4 days from anthesis to complete canopy senescence. The senescence score was fitted against thermal time using a five parameters monomolecular-logistic equation allowing the estimation of the timing of the onset and the rate of post-anthesis senescence. In each experiment, grain yield was reduced under low N (LN), with an average reduction of 2.2 t ha⁻¹ (29%). Significant N × genotype level interaction was observed for NUE. Crop N uptake at harvest on average was reduced from 227 kg N ha⁻¹ under high N (HN) to 109 kg N ha⁻¹ under LN conditions while N-utilization efficiency (grain DM yield per unit crop N uptake at harvest; NUtE) increased from 34.0 to 52.1 kg DM kg⁻¹ N. Overall genetic variability in NUE under LN related mainly to differences in NUtE rather than N-uptake efficiency (crop N uptake at harvest per unit N available from soil and fertilizer; NUpE). However, at one site there was also a positive correlation between NUpE and NUE at LN in both years. Moreover, across the 2 year/four site network, the N × genotype effect for NUpE partly explained the N × genotype effect for grain yield and NUE. Averaging across the 16 genotypes, the timing of onset of senescence explained 86% of the variation in NUtE amongst site-season-N treatment combinations. The linear regression of onset of senescence on NutE amongst genoytpes was not significant under HN, but at three of the four sites was significant under LN explaining 32-70% of the phenotypic variation amongst genotypes in NutE. Onset of senescence amongst genotypes was negatively correlated with the efficiency with which above-ground N at anthesis was remobilized to the grain under LN. It is concluded that delaying the onset of post-anthesis senescence may be an important trait for increasing grain yield of wheat grown under low N supply.     

The effects of nitrogen and iron fertilization on growth,yield and fertilizer use efficiency of soybean in a Mediterranean-type soil

Poor seed yield of soybean in Mediterranean-type environments may result from insufficient iron (Fe) uptake and poor biological nitrogen (N) fixation due to high bicarbonate and pH in soils. This study was conducted to evaluate the effects of N and Fe fertilization on growth and yield of double cropped soybean (cv. SA 88, MG III) in a Mediterranean-type environment in Turkey during 2003 and 2004. The soil of the experimental plots was a Vertisol with 176 g CaCO₃ kg⁻¹ and pH 7.7 and 17 g organic matter kg⁻¹ soil. Soybean seeds were inoculated prior to planting with commercial peat inoculants. N fertilizer rates were 0, 40, 80, and 120 kg N ha⁻¹ of which half was applied before planting and the other half at full blooming stage (R2). Fe fertilizer rates were 0, 200 and 400 g Fe EDTA (5.5% Fe and 2% EDTA) ha⁻¹. It was sprayed as two equal portions at two trifoliate (V2) and at five trifoliate stages (V5). Plants were sampled at flower initiation (R1), at full pod (R4) and at full seed (R6) stages. Application of starter N increased biomass and leaf area index at R1 stage whereas Fe fertilization did not affect early growth parameters. N application continued to have a positive effect on growth parameters at later stages and on seed yield. Fe fertilization increased growth parameters at R4 and R6 stages, and final seed yield in both years. This study demonstrated an interactive effect of N and Fe fertilization on growth and yield of soybean in the soil having high bicarbonate and pH. There was a positive interaction between N and Fe at the N rates up to 80 kg N ha⁻¹. However, further increase in N rate produced a negative interaction. Fertilization of soybean with 80 kg N ha⁻¹ and 400 g Fe ha⁻¹ resulted in the highest seed yield in both years. We concluded that application of starter and top dressed N in combination with two split FeEDTA fertilization can be beneficial to improve early growth and final yield of inoculated soybean in Mediterranean-type soils.     

Nitrogen efficiency in long-term wheat–maize cropping systems under diverse field sites in China

Efficiency of fertilizer N is becoming increasingly important in modern agricultural production owing to increasing food requirement and growing concern about environments. However, there is almost no study regarding its long-term efficiency in wheat and maize cropping systems. Long-term (15 years) experiments involving wheat (Triticum aestivum L.) and maize (Zea mays L.) rotations at five field sites with various soil and climate characteristics in China were used to determine the nitrogen (N) efficiency, including the physiological efficiency, recovery efficiency and N mass balance of soil–plant systems in response to different fertilization treatments. The present study consisted of nine treatments: unfertilized, N, phosphorus, potassium, straw and manure or their combinations. The contribution of N fertilizers to wheat yield was higher than to maize and suggested that wheat could be given priority over maize when determining N application rates. Uptake of 1 kg N produced 35.6 kg of wheat grain and 39.5 kg of maize grain. The deficit of N in soils without applied N ranged from 40 to 103 kg N ha⁻¹ year⁻¹, while N surpluses in soils with applied N fertilizers ranged from 35 to 350 kg N ha⁻¹ year⁻¹. The apparent accumulated N recovery efficiency (NRE_ac) varied widely from 4% to 90%: unbalanced fertilization and other soil limiting factors (such as aluminium toxicity) were associated with low NRE_ac. In the treatments of combination of N, phosphorus and potassium with normal application rates, the average of NRE_ac in four out of five sites reached 80%, which suggested that best management of N fertilizers could recover most of N fertilizers applied to soils. The results will be helpful to understand the long-term fate of N fertilizers and to optimize the N fertilization for agricultural practices and environment protection.