Study On Nitrogen Nutrient Of Plant-Weeds System In Semi-Humid Farmland

In semi-humid farmland ecosystems, weeds and crop competition at the same time in the soil moisture, nutrients, etc. Therefore this research bases on this point to study the existence of the weeds on the soil mineral nitrogen residual accumulation, crop yield and nitrogen utilization, as well as nitrogen losses on plant nitrogen uptake, and so on. In this thesis, crop density (wheat stage), weed treatments and nitrogen were arranged in a split-plot design with three replications. The experiments are the summer maize/winter wheat continuous cropping, and carry out by using manual loessial soil. In summer maize stage, weeds treatments have four different design, which were weed eradicated at maturing stages (area A), at jointing stages (area B), at trumpeting stage (area C) and at filling stage (area D), treatments for five levels of nitrogen, namely phosphorus in the foundation each hectare to execute nitrogen 0kg (PN₀), 45kg(PN₄₅), 90kg(PN₉₀), 135kg(PN₁₃₅) and 180kg(PN₁₈₀); In winter wheat stage,which were weed eradicated at maturing stages (A area), at over-wintering stage (area B), at reviving stage (area C) and at jointing stages (area D), fertilizer treatment have 7 different fertilizer rates, which were no fertilizer (CK),applying phosphorus (PN₀),applying nitrogen(P0N135), nitrogen and phosphorus mixed (PN45,PN90,PN135,PN180), Winter wheat increase low-density processing, that is, no fertilization (P0N₀), applying phosphorus (PN₀), the single-N (N135) and nitrogen at the same time P (PN135) .Through research come to the following conclusions:1. Not only planting density and fertilization affect the biological characteristics of winter wheat, but also significantly affected crop assimilation capacity. Under conditions that P used, the number of plants tillers and leaf area increase with the increases nitrogen; throughout the winter wheat growing period, leaf area index and transmittance was contrary to the trend of changes, the transmittance of a minimum at the flowering stage, leaf area index also appeared the highest value at flowering stage, the transmittance and the leaf area index related to grain yield closely, they have a significant correlation with grain yield (P <0.01);Under condition that phosphorus used, winter wheat SPAD Grain yield increased with the increase of nitrogen application rates; Low density SPAD were higher than normal density under same treatments; winter wheat SPAD decreased after flowing stage at both normal density and low density ; wheat Pn have no difference among different fertilizer treatments under two different plant density; Compared with normal density, wheat Pn were higher in low density with same fertilizer treatments. Wheat Pn and SPAD had a significant positive correlation. The research also discovered that; Invariable fluorescence (Fv), biggest fluorescence (Fm), foundation fluorescence (F0) and PSII latent activeness (Fv/F0) with grain yield present remarkable or extremely remarkable relationship ; Under two kind of planting densities, the PSII photochemistry efficiency (Fv/Fm) and the PSII latent activeness (Fv/F0) change rule is the same, namely they increases with the period of duration advancement, and they get highest in the flowering time, but decrease after flowering time.2. Farmland weeds species, such as biomass and so on are related with Planting density and fertilization Maize field weed in birth earlier period (jointing stage and trumping stage) main superiority population for cyperus rotundus linn and calystegia hederacea, but gives birth the later period, main dominant species for hairy crabgrass and bristlegrass; only phosphorus used can increase the maize field weed the density; The relationship between nitrogen rates and Weed N uptake reaches the remarkable level (R2=0.811*, n=5); The maize field weed three diversity index processes PN180 to be highest, the diversity index and nitrogen rates does not have certain relevance. The winter wheat field main dominant species are adescurainia sophia; Under the normal density, in phosphorus condition, , the density of weeds and biomass increase as the amount of nitrogen increased, weeds N uptake increased not significant with nitrogen increase; Under the low density, weed density, biomass and nitrogen uptake were higher than those of normal treatments at the same fertilizer treatments; in phosphorus conditions, the diversity index and evenness index with the increase of nitrogen reduced; The experimental study result discovered that three indices have the extremely remarkable linear correlation relations mutually(P<0.01).3. In summer maize season, soil profile NO₃^--N content increases along with increase of nitrogen, NO₃^--N and N content shows a linear correlation; during the growth of maize, soil NO₃^--N accumulation and NH₄⁺-N accumulation are highest in the trumpet-shaped object time, but are lowest in the filling time. In winter wheat season, under two kind of winter wheat planting density, NO₃^--N accumulation in Over-wintering stage reach highest, but after harvest is smallest; The research also indicated that under low wheat planting density, NO₃^--N and the NH₄⁺-N average accumulation is higher than normal planting density with same treatments, Reduces the planting density to have a tend to increases the soil nitrogen residual quantity.4. Grain yield is closely related to planting density and nitrogen rate. Summer maize biomass and nitrogen showed a significant linear correlation (r=0.965 **, n=5); The summer maize grain yield increases along with nitrogen increases, when weed eliminated at jointing stage, the grain average yield is highest, it is 4487.6kg/hm², but the whole period weed does not eliminated, the grain output is lowest, it is 3646.0kg/hm², the grain yield average loss is biggest when the whole period of weed does not eliminated. When weed eliminated at over-winter stage time, the grain average yield is highest, it is 5733.9kg/hm², but weed does not eliminated during the whole stage, the grain output is lowest, it is 4247.7kg/hm², the best elimination weeding time is before over-winter winter; When nitrogen rate is 135kg/hm², the grain average yield reaches the highest yield, it is 6669.3kg/hm². Normal density grain yield was higher than low density yield under the same fertilizer treatments; and normal planting density harvest index was higher low density; plant dry matter under low was higher than normal density, but the difference was not significant; under the low density, average DMT, DMTE and DMTP reduce 0.02g/plant, 3.96% and 4.71% compared to the normal density, so the reasonable planting density is more advantageous to the assimilation product to the grain transportation.5. In farmland ecology, weed N uptake impact assessment of nitrogen loss. The summer maize season, during the stage weed does not eliminated,nitrogen fertilizer use efficiency is lowest, which is 23.75% equally; When weed eliminated at trumpeting stage, nitrogen fertilizer use efficiency is highest, it is 30.77% equally. The winter wheat season, the nitrogen use efficiency presents a increasing tend with nitrogen use, when weed eliminated at over-winter stage, nitrogen fertilizer use efficiency is highest, which is 45.67% equally. After Summer maize harvest, mine nitrogen in the soil of increase as the increase of nitrogen rates, between the two assumes the extremely remarkable linear correlation relations(P<0.01). The winter wheat season, along with nitrogen rates increase, in the soil the residual mine nitrogen also presents the tendency of increase. The summer maize season, when weed nitrogen uptake did not considered, the nitrogen loss of PN₄₅, PN₉₀, PN₁₃₅ and PN₁₈₀ increase7.85%, 6.54%, 4.82% and 6.93% separately compared weed nitrogen uptake considered. Under different weed treatments ,when weed nitrogen uptake did not considered, the nitrogen loss of area A, Area B, Area C and Area D increase 10.54%, 4.97%, 14.27% and 2.99% separately compared weed nitrogen uptake considered; In the winter wheat season, when weed nitrogen uptake did not considered, the nitrogen loss of PN₄₅,PN₉₀,PN₁₃₅å’ŒPN₁₈₀ increase 5.12%,7.49%,9.64% and 18.39%separately compared weed nitrogen uptake considered. When to estimate field ecosystem nitrogen balance, it should consider weeds nitrogen uptake to reduce the nitrogen loss estimator.