Spring Maize Response To Soil Nitrogen Supply And Indices Of Nitrogen Recommendation

Nitrogen (N) is one of the most limiting nutrients for maize production in Northeast China Plain, it is necessary to investigate maize response to N application as affected by level of soil nitrogen deficiency and to monitor plant N uptake and soil N supply to ensure an adequate N supply for maize, so as to optimize plant growth, improve N use efficiency, and to reduce N losses. Chlorophyll meters (Soil Plant Analysis Development, SPAD) and soil mineral nitrogen (Nmin) or nitrate N test have been effectively used to nondestructively quantify N status during vegetative and reproductive stages of maize growth. However, little work has been done in relation to maize response to different N application rates as affected by level of soil nitrogen deficiency, and nitrogen recommendation for maize based on leaf SPAD and soil nitrate-N remains unclear in Northeast China Plain. Therefore,four field trials combined with plant analysis and soil determination were carried out to investigate maize response to different N application rates as affected by level of soil nitrogen deficiency, and to probe an appropriate leaf SPAD value and soil nitrate N content for N management in spring maize. The four experimental sites included Liufangzi and Fanjiatun (as representative of the soils with a lower level of Nmin), and Taojia and Yushu (as representative of the soils with a higher level of Nmin). The main findings are as following:1.The dynamic changes of total biomass of maize under different level of soil nitrogen deficiency could be described by Logistic curve equation, The increasing duration and increasing rate of biomass were obviously influenced by different level of soil nitrogen deficiency and different N application rates. The fastest increasing duration was found to be from jointing to tasseling, and from silking to grain-filling, hence top-dressing N at jointing and tasseling would have profound role for biomass as well as yield formation. The highest accumulation rate was found in the treatment of 280 kg N/hm2 and 300 kg N/hm2 in Liufangzi site with a lower Nmin level, while N application in Yushu site with a higher Nmin level decreased the highest accumulation rate compared to control with no N applied. Nitrogen application rates for maximum and optimum yields in soils with a lower Nmin level were found to be higher than those with a higher Nmin level.2. In general, N accumulation in maize increased with enhancing N application rate for four experimental sites, the agronomic efficiency, nitrogen recovery, and partial factor productivity of maize in the soils with a lower Nmin were found to be higher than those with a higher Nmin. The accumulation process of nitrogen in spring maize plants under different N application rates in four experimental sites could be described by Logistic curve equation. The highest N absorption rates (HAR) of N occurred in middle growing season(from jointing to tasseling), indicating that topdressing N at jointing stage is needed to improve N recovery. High HAR and its early occurring could be achieved with the appropriate N application rate for the four experimental soils with different Nmin.3. SPAD value in the youngest fully expanded leaf increased with enhancing nitrogen application rates for both Liufangzi and Fanjiatun sites, while there was no significant increase when over 240 kg N/hm2 was applied. A significant correlation was found between SPAD value and leaf N concentration, leaf N uptake, N application rate, and grain yield at jointing of maize, SPAD value could well reflect plant N status; The optimal SPAD thresholds at jointing stage in maize c.v. Zhengdan958 were 56～58, and it was observed that applying 20 kg N/hm2 could upregulate 1 unit of SPAD value. Therefore, the SPAD thresholds value of 56～58 were recommended for topdressing N at jointing stage for maize c.v. Zhengdan 958.4. Soil nitrate N content and N accumulation tended decreased during early-middle growing season, and then increased in the late growing season for each N supplying treatment. In Fanjiatun site, an satisfactory nitrate N level could be maintained when 240 kg N/hm2 was applied. The maize yield increased linearly increased with enhancing nitrate N accumulation in soil layer of 0-90 cm until a maximum, then kept unchanged in a big range, the relationship between grain yield and nitrate N accumulation could be described by a linear plus plateau model. With maize yield and environmental protection considered comprehensively, the nitrate N content in top 90cm soil layer should be maintained at an appropriate level from 134～145 kg/hm2 during maize growth season.