Effect of long-term fertilization on soil nitrate distribution

A thirteen years long-term field fertilizer experiment was conducted to monitor the effect of different fertilization on soil nitrate distribution. The results showed: (1) Applying relative excessive N fertilizer could result large quantities of NO3- residue and NO3- movement downward in soil profiles; amending phosphate fertilizer or organic manure with nitrogen fertilizer together could significantly improve the status of NO3- leaching downward due to the balanced uptake of nutrients by crops. ( 2) Appropriate amounts of nitrogen fertilizer which was equal or smaller than the optimal fertilization rate could not result in more NO3- leaching in Northern China. (3) Precipitation influenced the amounts and depth of soil NO3- leaching: NO3- could move to 80 cm depth or below at autumn or at the next spring when rainfall was higher during the rainy season through July to September in North China.

Effects of soil nitrate:ammonium ratio on plant carbon:nitrogen ratio and growth rate of Artemisia sphaerocephala seedlings

Can soil nitrate： ammonium ratios influence plant carbon： nitrogen ratios of the early succession plant？ Can plant carbon： nitrogen ratios limit the plant growth in early succession？ To address these two questions, we performed a two-factor （soil nitrate： ammonium ratio and plant density） randomized block design and a uniform-precision rotatable central composite design pot experiments to examine the relationships between soil nitrate： ammonium ratios, the carbon： nitrogen ratios and growth rate of Artemisia sphaerocephala seedlings. Under adequate nutrient status, both soil nitrate： ammonium ratios and plant density influenced the carbon： nitrogen ratios and growth rate of A. sphaerocephala seedlings. Under the lower soil nitrate： ammonium ratios, with the increase of soil nitrate： ammonium ratios, the growth rates of plant height and shoot biomass of A. sphaerocephala seedlings decreased significantly; with the increase of plant carbon： nitrogen ratios, the growth rates of shoot biomass of A. sphaerocephala seedlings decreased significantly. Soil nitrate： ammonium ratios affected the carbon： nitrogen ratios of A. sphaerocephala seedlings by plant nitrogen but not by plant carbon. Thus, soil nitrate： ammonium ratios influenced the carbon： nitrogen ratios of A. sphaerocephala seedlings, and hence influenced its growth rates. Our results suggest that under adequate nutrient environment, soil nitrate： ammonium ratios can be a limiting factor for the growth of the early succession plant.

The characterization of soil profile distribution for nitrate leached in the paddy soil

Experiment was conducted for five successiveyears under large undisturbed monolith lysime-ters(2m×2m in square,l m in depth).Thesoil was silty clay loam texture and had a con-tent of total N 1.55 g/kg.The soil was flood-ed with penetration rate controlled at approxi-mate 3 mm per day in duration of double-riceseason and laid fallow and natural in winterand spring.Results showed that nitrate was the mainform of nitrogen in percolates.The change of

Effects of irrigation regimes on soil NO_(3)^(-)-N, electrical conductivity and crop yield in plastic greenhouse

Developing water-saving irrigation regimes has important practical significance not only in alleviating the crucial water shortage,but also in controlling soil salinization for the protected cultivation in eastern China.A field study with six treatments was conducted to evaluate the effects of different irrigation regimes with subdrainage systems on the soil nitrate nitrogen,salinity and moisture,also evaluate the effects on tomato growth,fruit yield and irrigation water use efficiency(IWUE).The treatments were distinguished by three different irrigation amounts of 310 mm,360 mm and 410 mm,and two irrigation frequencies of 7 and 11 times.Results showed that the irrigation amount had significant effects on the soil NO_(3)^(-)-N and electric conductivity(EC).A positive correlation was detected between soil NO_(3)^(-)-N(x)and EC(y)at 0-20 m depth after harvest,with a linear equation of y=0.063x-0.670.Soil volumetric moisture at 0.10 m and 0.20 m depth was increased as the irrigation amount increased.Moreover,a higher amount of irrigation increased the fruit yield but reduced the IWUE of tomato.It was also found that smaller irrigation amounts combined with frequent intervals could increase fruit yield and IWUE.However,the fruit quality of tomato had a significant(p<0.05)negative correlation with irrigation amount.Therefore,the parameters of irrigation regime including the irrigation amount and intervals should be considered comprehensively in order to find a compromise between salinity control and irrigation water use efficiency improvement.

Effect of invasion by Hyptis suaveolens on plant diversity and selected soil properties of a constructed tropical grassland

Aims Hyptis suaveolens(L.)Poit is an important invader of the tropical and sub-tropical regions of the world.In our study,it has been inves-tigated that how does the H.suaveolens invasion regulate plant spe-cies diversity across the seasons in the dry tropical grassland.We hypothesized that a shift in soil inorganic-N availability is caused by invasion,and this shift is integral to access the invasion effect on plant diversity.Methods The study was performed in experimental plots at the Botanical Garden of the Banaras Hindu University(25°16′3.3″N and 82°59′22.7″E),Varanasi,Uttar Pradesh,India.Five replicates(each,2×2m)of non-invaded grassland plots(NIG)and five grassland plots invaded with H.suaveolens(IG)were established.These plots were constructed by transplanting indigenous grassland patches from an adjacent native grassland.In the invaded plots,20 indi-viduals of H.suaveolens were transplanted per plot.After 1 year of establishment,diversity attributes and soil properties were recorded from these plots in three seasons as per standard protocol.Important Findings The results indicated that Hyptis invasion negatively affects plant diversity,with relatively higher impact in rainy season as compared to the winter season.IG exhibited lower soil mois-ture content and temperature than NIG in rainy season,whereas soil ammonium-N,nitrate-N,total inorganic-N,N mineralization registered higher values for IG than NIG in both rainy and win-ter season.Diversity indices were negatively correlated with soil inorganic-N pool and N mineralization.However,these indices were positively correlated with microbial biomass carbon(MBC),and the correlation coefficient for this relationship was higher for rainy season as compared to winter.Species richness(r=0.65)and Shannon diversity(r=0.757)were significantly correlated with the ratio of ammonium-N to nitrate-N.The negative effect of invasion by H.suaveolens on the plant diversity is possibly mediated by the effect of invasion on N mineralization processes(mainly nitrification)and the availability of soil inorganic-N pools.The study indicates that Hyptis invasion has an enormous poten-tial to change the structure and composition of plant communities in the dry tropical grasslands.