| Whether it is natural ecosystem or farmland ecosystem, root-soil interface dynamics is regarded as a key point to limit nutrient mobilization, availability and uptake by plants. The root growth is one of the most essential drivers to modify rhizosphere processes in association with efficient nutrient acquisition and utilization. It is extremely important to deepen the understanding of root-induced rhizosphere processes for increasing nutrient bioavailabilityand nutrient use efficiency through maximizing root/rhizosphere biological potential rather than heavily depending on the external input of chemical fertilizers. We hypothesized that the target can be achieved through positioningly manipulating root morphological and physiological traits as well as intensifying rhizosphere chemical processes under field conditions, which is critical for sustainable crop production. Numerous studies show that plant roots with an excellent morphological and physiological plasticity, can effectively respond environmental conditions. The response extent depends on the tensity of nutrient supply, nutrient forms, nutrient combination, position, and plant genotype etc. In the intensive system, we want to test whether root and rhizosphere nutrient management can effectively improve root growth, nutrient uptake and yield. In the present study, maize was grown at different treatments with uniform or localized nutrient supplies on a calcareous soil under field or controlled greenhouse conditions. The effect of localized supply of different N form with phosphorus on root growth, nutrient uptake (macronutrients and micronutrients) and yield has been studied through pot or field experiments. The main results and conclusions are as followed:1. Specific nutrient management significantly promoted root growth and nutrient accumulation of maize at seedling. The criticals level of applied P and N were50kg ha-1and70kg N ha-1, respectively. Shoot dry weight would not be improved when the amount of applied P was more than critical level. But, maize shoot or root growth was hampered when the applied N was μp to135or195kg N ha-1.2. Compared with banding Urea+P and the mixing treatments, banding P plus ammonium not only increased the length and density of first-lateral root in the fertiliser-banded layer, but also enhanced shoot N and P uptake rates per root dry weight or root length. Root proliferation and increased uptake rate could be all benefit for the nutrient accumulation in maize.3. Localized supply of NH4-N+P at seeding stage and jointing stage improved maize growth both at seedling and later stages. The average root length density increased by156-173%at the depth of20-30cm and by87-196%at30-40cm in localized NH4-N+P application. Localized supply NH4-N+P at seedling and jointing stages enhanced maize growth at later stage and maize grain.4. The results confirmed that localized NH4-N+P supply on calcareous soil enhanced zinc (Zn) and iron (Fe) accumulation in maize via modifying root traits and rhizosphere acidification. Compared with localized Urea+P, localized NH4-N+P supply may improve the availability of Zn and Fe in the soil and improve root proliferation, leading to improved accumulation of Zn and Fe and grain Zn/Fe concentration.5. The results showed that localized NH4-N+P supply on calcareous soil elicited an ammoniu-dependent enhancement of maize root growth and nutrient uptake. The NH4+-N supply in localized NH4-N+P treatment accounted for over50%of variation in plant growth rate (PGR), shoot dry matter and grain yield at maturity in2012and2013. There was a positive linear correlation between kernel number per ear and PGR. The grain yield and N concentration in grain increased by10-48%and4-27%, respectively, in localized NH4+-N, NH4:NO3(1:1)+P and NH4+-N+P treatments compared with those in CK (no N and P), localized P and NO3-N+P in two years. |
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