Nitrogen Rates, Sources And Management Effects On Physiological And Harvest Attributes Of Wheat And Corn

Nitrogen (N) is one of the most important nutrients influencing both yield and grain quality, and N supply is one of the few production factors that can be controlled and which is known to effectively influence crop performance. However, current N management systems for corn have resulted in low nitrogen use efficiency (NUE). Nitrogen leaching and environmental pollution have attracted the attention of the worldwide researchers. With good management of N fertilizer, N losses and economic loss can be kept to a minimum and improve protection of water quality and crop grain yield. The objectives of this study were to evaluate N application rates, N sources and management effects on physiological characteristics and grain yield of wheat at the filling stage and corn at vegetable stage and after silking stage. The results can provide theoretical proof for high quality and high yield of crop and good management of N fertilization; implement the development of precision agriculture. It got the following main conclusions:1. The chlorophyll content, peroxidase (POD) activities and catalase (CAT) activities of leaf decreased during the filling stage of wheat, the malondialdehyde (MDA) content increased during the filling stage of wheat. The chlorophyll content, POD activities and CAT activities of different leaf position appeared to decline in the order of the flag leaves, the second leaves from top and the third leaves from top in wheat. The MDA content of different leaf position appeared to increase in the order of the flag leaves, the second leaves from top and the third leaves from top of wheat during the filling stage of wheat. Different farming modes and N application rate significantly influenced the chlorophyll content, POD activities, CAT activities and MDA content of leaves in wheat. Straw multh cultivation modes with 120 kg N ha-1, the chlorophyll content of leaf was the highest, the speed of flag leaf aging was slow, the extent of declining metabolizability was slow too. And it was of great benefit to growth and filling at the late filling stage of wheat.2. The trend of starch content was opposite to the trend of total soluble sugar content and sucrose content in wheat grains during the filling stage of wheat. The soluble sugar content and sucrose content of grains decreased, and the starch content increased during the filling stage of wheat. Different farming modes and N application rate significantly influenced the soluble sugar content, sucrose content and starch content. Compared with flat farming, the total soluble sugar contents and sucrose contents in straw mulching and plastic film-mulching were higher than that in flat farming, the starch contents in straw mulching and plastic film-mulching were higher than that in flat farming during the filling stage, and satiety index of wheat grain and the yield were all higher than that in flat farming. Nitrogen enhanced the total soluble sugar contents and sucrose contents during the early filling stage, decrease the total soluble sugar contents and sucrose contents during the lately filling stage. Nitrogen promoted the ability supplying utilizing assimilate and the starch accumulation of grain in wheat. However, excess N didn't enhance the anabolism of total soluble sugar and sucrose of grain and the ability supplying utilizing assimilate in wheat. Straw multh cultivation modes and plastic film-mulching with 120 kg N ha-1, the total soluble sugar and sucrose were higher in the early filling stage, the ability supplying utilizing assimilate were strong and increased the starch accumulation of grain in wheat during grain filling stage. That was of great benefit to growth and filling at the late filling stage of wheat with straw multh or plastic film-mulching and 120 kg N ha-1.3. SPAD reading, net photosynthetic rate (PN), leaf area index (LAI), aboveground dry biomass, canopy chlorophyll density (SPAD×LAI) and canopy photosynthetic capacity (PN×LAI) of the uppermost fully developed leaves of the corn increased with basal N rates increasing before side-dressing. However, Dualex reading showed an opposite trend in response to basal N rates. Split N application significantly increased SPAD reading, however, no significant influence on Dualex reading and PN of leaf. Split N application significantly increased corn grain yield compared to only one application at sowing, and 45 kg N ha-1 was better than 20 kg N ha-1. Under our experimental condition, a total N application with 113 kg N ha-1 did not produce the same corn grain yield as saturated N rate plot (SAT225). Both SPAD and Dualex readings showed significant correlation with corn plant N concentration, and then can be used as an instant and non-destructive diagnostic tools for corn N status evaluation.4. SPAD reading of ear leaf, aboveground dry biomass and corn grain yield increased with increasing side-dressing N rates, Dualex reading decreased with increasing side-dressing N rates after silking. The SPAD-N sufficiency index (SPAD-NSI) of side-dressing N with 101, 135, 169 and 203 kg N ha-1 were always higher than 0.95 at all samplings dates. The Dualex-N sufficiency index (Dualex-NSI) of side-dressing N with 101 kg N ha-1 were higher than 0.95 from 18 d to 46 d; the Dualex-N NSI of side-dressing N with 135, 169 and 203 kg N ha-1 were also higher than 0.95 at all samplings dates. SPAD reading, Dualex reading, SPAD-NSI and Dualex-NSI were strongly related to side-dressing N rates. The maximum yield has been reached when side-dressing N with 101 or 135 kg N ha-1 at jointing stage. When maximum yield has been reached, any additional N has no significant effect on SPAD reading, Dualex reading, aboveground dry biomass and corn grain yield. There was no significant difference between splitting the N into two applications and put all N at sowing on grain yield, however, splitting the N into two applications significantly decreased the N application rate and growers'inputs.5. When established the N saturated reference plot in corn, water status and N application methods have no influence on N saturated reference plot establishment. Based on this study, growers can either broadcast at sowing or band along the rows at a later time when corn is emerged, which will give flexibility to N saturated reference plots establishment. All N sources (calcium ammonium nitrate (CAN), urea ammonium nitrate (UAN), urea (URE), polymer-coated urea (PCU), and environmentally smart N (ESN)) had the equivalence performance on N saturated reference plot establishment in our experimental conditions. However, when consider the environmental and economic factors, URE and UAN were recommended as adequate and affordable N sources for reference plot establishment. PN or relative photosynthetic capacity (RPC) was found to be a better indicator of photosynthetic performance under contrasting N supply than Fv/Fm (or Fv'/Fm') or relative chlorophyll fluorescence capacity (RCFC).6. The instant, non-destructive and sensitive parameters for N diagnostic criteria were compared: chlorophyll meter (SPAD), normalized difference vegetation index (NDVI), Dualex and combined SPAD and Dualex measurements in the form of the ratio Chl/DUAD in this study. SPAD readings and Chl/DUAD were the earliest and most stable indicators when expressed in the form N sufficiency index (NSI). NDVI was measured with Greenseeker could evaluate the N status in crop population, so, NDVI was also a suitable indicators for evaluation N status when expressed in the form NSI. Dualex reading varied and was instability among years when expressed in the form NSI, therefore, Dualex reading was not a suitable indicator for calculationg NSI in corn. Water status and N application methods have no significant influence on SPAD reading, Dualex, NDVI and Chl/DUAD when expressed in the form NSI.7. In the soil or terrain properties including soil electrical conductivity (ECa), elevation, slope, curvature of the terrain, and aspect of the terrain, ECa and elevation were the dominant factors influencing the NDVI both in null N and saturated N rate (250 kg N ha-1). When using NDVI_N sufficiency index (NDVI_NSI) evaluated the N status in corn, none of soil or topographic properties was the important factor influencing NDVI_NSI of corn. Hence, using NDVI_NSI for site-specific N management can eliminate the soil or topographic properties on corn growth, decreased the economic input of growers, decreased the N loss and environmental pollution, and improved the grain yield of corn.