B. L. Ma

Nitrogen uptake and use of two contrasting maize hybrids differing in leaf senescence

In eastern Canada, the use of fertilizer N has been identified as the most energy-consuming component of maize (Zea mays L.) grain production. As the economic and environmental costs of excessive N fertilization rise, there is an increased emphasis on selection of hybrids with greater N use efficiency (NUE; defined as the ratio of the amount of 15N recovered in grain or stover dry matter to the amount of fertilizer 15N applied to the soil in this study). Using an 15N-labelling approach, a field study was conducted on a tile-drained Brandon loam soil (Typic Endoaquoll) on the Central Experimental Farm at Ottawa, Canada (45°22′ N, 75°43′ W) in 1993 and 1994. Fertilizer N uptake and partitioning within the plant in relation to dry matter changes were monitored during development of a current stay-green maize hybrid and an older early-senescing hybrid grown with three fertilizer N levels (0, 100, 200 kg N ha-1). Dry matter, N concentration and15 N atom% enrichment of plant components were determined at five growth stages. The current stay-green hybrid, ‘Pioneer 3902’ had greater NUE than the old early-senescing hybrid, ‘Pride 5’, which was associated with 24% more dry matter production and 20% more N uptake during grain fill for Pioneer 3902. There was no indication of greater allocation of N to the grain in Pioneer 3902. Our data suggest that prolonged maintenance of green leaf area for photosynthate production during grain fill and the ability to take up available soil N later in grain filling are characteristics of maize hybrids with greater NUE.

Effects of N-deficiency and timing of N supply on the recovery and distribution of labeled 15N in contrasting maize hybrids

Little information exists on the pattern of nitrogen (N) uptake, remobilization and N use efficiency (NUE) in Leafy and stay-green (SG) maize (Zea mays L.) genotypes. A pot experiment was conducted under controlled nutrition and growing conditions to determine the response of Leafy and SG maize genotypes to different levels of N-deficiency and timing of N supply. Three contrasting maize hybrids, ‘Pioneer 3905’ (a conventional hybrid with moderate SG characteristics), ‘Pioneer 39F06 Bt’ (with a high score of SG trait) and ‘Maizex LF850-RR’ (with a Leafy trait) were grown in 6 L plastic pots. Five different N treatments [no supply of N until V8 (N1), no supply of N after V8 (N2), no supply of N after silking (N3), no supply of N beyond 3 weeks after silking (N4), and continuous N supply from emergence to physiological maturity (N5; standard check)] were imposed through modified Hoagland solution applied manually. Labeled 15N of 5% 15N2–NH4NO3fertilizer was applied at 3 g per pot at the start of each schedule N treatment. Total amounts of N applied in different treatments were 3.13, 1.32, 1.90, 2.63 and 3.40 g, respectively in N1, N2, N3, N4 and N5. Dry matter, N concentration, 15N (atom% enrichment) and NUE were determined in roots, stalk, leaves and grains at crop maturity. The three contrasting hybrids did not differ in grain yield, total N acquisition, partitioning of 15N and NUE. Restriction of N supply until V8, and from V8 to physiological maturity significantly reduced grain yield and N-uptake in all hybrids. Irrespective of the level of N-deficiency in plant and timing when the labeled fertilizer was applied, the amount of 15N recovered in the matured plant was the same in all N treatments. It has been evident that maize continued to take up N beyond 3 weeks after silking and the later N was applied during the development, the higher proportion of it was partitioned to grains. Of the total 15N uptake, 78% was partitioned to kernels in the N4 treatment compared to only 61% in the control. Our data showed no evidence of differential N uptake, remobilization and NUE in the SG or Leafy hybrids tested, but the timing of N application and level of N-deficiency in plant significantly influenced N uptake, remobilization and N-dynamics in maize.

Crop rotation and nitrogen effects on maize susceptibility to gibberella (Fusarium graminearum) ear rot

An experiment was established in 1992 in eastern Ontario, Canada to determine the effects of crop rotation (continuous maize, soybean-maize and alfalfa-maize) and nitrogen (N) amendment [0, 100 and 200 kg N ha−1 of fertilizer (NH4NO3), and 50 and 100 Mg ha−1 (wet wt.) each of stockpiled and rotted dairy manure] on maize production and soil properties. From 1997 to 1999, an additional study was added to the experiment to investigate treatment effects on the susceptibility of maize hybrids to gibberella ear rot. A moderately resistant and a susceptible hybrid were planted in each plot and inoculated with a macroconidial suspension of Fusarium graminearum by both the silk channel injection and the kernel-wound techniques. At harvest, ears were rated for the severity of disease symptoms and harvested kernels were analyzed for the mycotoxin deoxynivalenol (DON). The greatest number of significant N effects were found in the continuous maize treatments and with the susceptible hybrid. Most N amendments decreased both disease severity and DON accumulation in the susceptible hybrid. The most consistent effect was a decrease in disease severity with 100 kg N ha−1 fertilizer and an increase in disease severity with the higher rate of 200 kg N ha−1. This study is the first to report on the effects of soil N amendments on gibberella ear rot susceptibility.

A review of the system of rice intensification in China

BackgroundContinually increasing food demand from a still–growing human population and the need for environmentally–friendly strategies for sustainable agricultural development require innovation and further enhancement of cropping systems’ factor productivity. The system of rice intensification (SRI) has been proposed as a suitable strategy to improve rice yields with reduced input requirements, most notably water and seed, while enhancing soil and water quality because agrochemical applications can be cut back.Scope and conclusionsThis review examines the performance of SRI methods in China since first introduced in 1999 and considers their implications for further agricultural systems development. A meta–analysis of studies conducted over the past decade in China indicates that SRI methods have been increasing rice yield in comparison trials with current improved practices by more than 10xa0%. These higher yields are being attained with reduced field requirements for irrigation water and with much–reduced seed rates. This can lower farmers’ costs of production and enhance their net income from rice. Such benefits are accompanied by other advantages reported by various researchers in China and elsewhere, such as greater disease resistance, higher nitrogen use efficiency, enhanced photosynthetic rates, and improved physiological traits.With appropriate modifications for local conditions, there is increasing evidence that SRI principles and practices can offer an environment–friendly strategy for sustainable agriculture in China and elsewhere. This review considers Chinese and other research on opportunities for improving agricultural production and food security with less strain on environmental resources, and for helping farmers cope with increasing climatic stresses now and in the future.

Timing and method of 15nitrogen-labeled fertilizer application on grain protein and nitrogen use efficiency of spring wheat

ABSTRACT Grain protein content is one of the most important quality constraints for bread wheat (Triticum aestivum L.) production in eastern Canada. A field experiment was conducted for two years (1999 and 2000) on the Central Experimental Farm, Ottawa, Canada, to study whether split application of nitrogen (N) fertilizer improved grain protein content and nitrogen-use efficiency (NUE). Two cultivars (‘Celtic,’ as N-responsive and ‘Grandin’, as N-non-responsive) were grown using three different N doses and application methods: (1) 100 kg N ha−1 as NH4NO3, soil-applied at seeding with 15N2-labeled NH4NO3 to microplots, (2) 60 kg N ha−1 soil-applied at seeding plus 40 kg N ha−1 foliar-applied at the boot stage with 15N2-labeled urea to microplots, and (3) 90 kg N ha−1 as soil-applied at seeding plus 10 kg N ha−1 foliar-applied at the boot stage with 15N2-labeled urea to microplots. Plants were sampled at heading and maturity. While dry-matter production and grain yields were not affected by the treatments in either year, N application methods influenced tissue N concentration and NUE. In 1999, extended drought stress led to significant yield reduction; in 2000, foliar application of 10 kg N ha−1 at the boot stage significantly increased grain N concentration when grain protein was under the limit for bread quality, suggesting that later-applied N can contribute to grain protein content. At maturity, the average NUE was 22.3% in 1999 and 34.5% in 2000, but was always greater when all N was applied at seeding (42.5%) than when N was foliar-applied at the boot stage (18.5% to 24.5%). We conclude that application of a small amount of fertilizer N at the boot stage can improve the bread-making quality of spring wheat by increasing grain protein concentration.

Photoperiod Effect on Phytochrome and Abscisic Acid in Alfalfa Varieties Differing in Fall Dormancy

ABSTRACT Short daylength (SD) is the main environment-induced factor leading to fall dormancy (FD) in alfalfa (Medicago sativa L.). However, the physiological mechanisms causing varietal differences in shoot growth and fall dormancy of alfalfa crop are not fully understood. The objective of this research was to explore the physiological principles regulating FD in alfalfa by examining phytochrome B (PhyB) and abscisic acid (ABA) contents in response to photoperiodic reaction and fall dormancy. Three alfalfa varieties having different levels of fall dormancy were examined for ABA and PhyB concentrations under three photoperiod conditions (8, 12, and 16 h photoperiod). Our results showed that the leaf PhyB concentration was the greatest in the highly dormant variety, intermediate in semi-dormant, and the lowest in non-dormant varieties. Across all the varieties, PhyB concentration under 8-h photoperiod was 9.2% and 37.4% higher than those under 12-h and 16-h photoperiod (LD), respectively. Accordingly, the ABA concentration was also greater in highly dormant varieties. When subjected to LD conditions, all varieties reached flowering although it took additional 2–4 d for dormant varieties to blossom than non-dormant ones. It was evident that SD treatment induced the biosynthesis of PhyB and ABA. Our data indicate that large differences in PhyB and ABA concentrations exist among alfalfa varieties differing in fall dormancy.

NITROGEN NUTRITION ON LEAF CHLOROPHYLL, CANOPY REFLECTANCE, GRAIN PROTEIN AND GRAIN YIELD OF WHEAT VARIETIES WITH CONTRASTING GRAIN PROTEIN CONCENTRATION

Wheat cultivars (‘AC Barrie’, ‘Brook Field’, ‘Hoffman’, and ‘Norwell’) with different protein concentrations were compared under four nitrogen (N) levels (0, 50, 100 and 150 kg ha−1) in an environment-controlled greenhouse, and the same experiment with an additional N level (200 kg N ha−1) was repeated in the field in 2007. In the greenhouse experiment, application of 100 kg N ha−1 resulted in significantly greater grain yield due mainly to higher number of grains per spike and heavier mean grain weight; in the field study, the 150 kg N ha−1 treatment produced the greatest yield (P<0.01) primarily due to more number of grains per spike. Crude grain protein percentage was increased significantly with each increment of N up to the highest level; however, protein yield (kg ha−1) increased significantly with fertilizer up to 150 kg N ha−1. Leaf chlorophyll contents were increased linearly with increment of N levels up to 150 kg ha−1 both in the greenhouse and field trials while leaf area indices continued to increase up to the highest application rate (200 kg N ha−1). Canopy reflectance, expressed as normalized difference vegetation index (NDVI), attained maximum value with 150 kg N ha−1 in the field experiment. Among the varieties tested, “Hoffman” out-yielded other three varieties due to heavier grain weight. Although highest grain and/or plant crude protein content were recorded in ‘AC Barrie’, it was the variety ‘Hoffman’ that produced the highest total protein (kg ha−1) with largest NDVI and leaf area index (LAI) values.

Salinity Effects on Yield and Yield Components of Contrasting Naked Oat Genotypes

ABSTRACT Global crop production systems are challenged by the increasing areas of saline soil in arid and semi-arid regions. Two naked oat (Avena sativa L.) lines (‘VAO-7’ and ‘VAO-24’) with distinct seedling tolerance to salinity were subjected to six levels of salt concentrations in a controlled greenhouse, and the response of yield and yield components to salinity stress was determined. The salt treatments 50, 100, 150, 200, and 250 mM sodium chloride (NaCl) (corresponding to EC: 3.42, 6.74, 9.66, 12.40, 15.04 dS m−1) imposed through modified Hoagland solution. Plain Hoagland was used as control. Complete nutrient elements were provided during the entire growth period. At maturity, the number of tillers with emerged heads was counted; the plant was then harvested and separated into shoots, seeds, and roots. Both plant height and days to maturity were shortened with increasing salt stress. Among the yield components, spikelet, tiller number, and grain dry weight per plant were significantly reduced by increasing salt concentration. Number of spikelets and grain weight per plant were the most salt-sensitive yield components. Thousand grain weight also varied as salinity stress increased. Harvest index remained relatively unchanged until the salinity reached 150 mM and higher. Our data indicate that grain yield reduction in oat due to salinity stress is associated with reduced number of grains per plant and mean grain weight.

LEAF PHOTOSYNTHESIS, BIOMASS PRODUCTION AND WATER AND NITROGEN USE EFFICIENCIES OF TWO CONTRASTING NAKED VS. HULLED OAT GENOTYPES SUBJECTED TO WATER AND NITROGEN STRESSES

Water and nitrogen (N) are the two most important factors influencing the growth and yield of oat (Avena sativa). A pot culture study was conducted to determine the physiological and biomass production of contrasting oat genotypes to water and N supply conditions. With sufficient water, biomass yield of the naked ‘Shadow’ was 12.4% and 10.0% greater than ‘Bia’ in the treatments 750 and 1250 mg N pot−1, respectively, but ‘Bia’ produced greater grain yield than ‘Shadow’. Under severe water stress conditions, increasing N supply decreased PN mainly due to the reduction of gs and E. ‘Shadow’ had higher chlorophyll and leaf N than ‘Bia’, while there were no differences in plant total N, NuptE and NUE. With increasing N application and water stress, WUEL and WUEP both increased. NUE was inversely related with increasing N rates and water stress levels, resulting in a trade-off relationship between WUEP and NUE.

NITROGEN, PHOSPHORUS, AND POTASSIUM NUTRIENT EFFECTS ON GRAIN FILLING AND YIELD OF HIGH-YIELDING SUMMER CORN

A three-site-year field experiment was conducted to determine nitrogen (N), phosphorus (P), and potassium (K) fertilizer effects on grain filling dynamics and yield formation of high-yielding summer corn (Zea mays L.) in a wheat (Triticum aestivum L.)-corn double crop cropping system. Application of combined NPK fertilizers resulted in the greatest grain yield, largest grain number and grain weight when compared with the treatments receiving N, NP, or NK. Grain filling rate and duration, grain volume, and grain yield increased with NPK rates; however, doubling the rate of 180 kg N ha−1, 40 kg P ha−1, and 75 kg K ha−1 fertilizer only led to minimal increases in grain filling rate (0.8%), grain filling duration (1.6%), grain volume (1.3%) and grain yield (0.4%). Our results suggested that for the high-yielding summer corn, a combined NPK fertilization is required to enhance grain filling and yield, and that under well-fertilized circumstances, limited increases in both grain filling and sink capacity might be the main factor restricting further yield improvement.