Effects of N Forms and Rates on Vegetable Growth and Nitrate Accumulation

Experiments were carried out on a vegetable field with Peking cabbage(Brassica pekinensis (Lour.) Rupr.), cabbage (Brassica, chinensis var. oleifcra Makino and nemoto),green cabbage (Brassica chinensis L.), spinach (Spinacia oleracea L.) and rape(Brassica campestrisL.) to study the effects of N forms and N rates on their growth and nitrate accumulation. Theresults indicated that application of ammonium chloride, ammonium nitrate, sodium nitrate and ureasignificantly increased the yields and nitrate concentrations of Peking cabbage and spinach.Although no significant difference was found in the yields after application of the 4 N forms,nitrate N increased nitrate accumulation in vegetables much more than ammonium N. The vegetableyields were not increased continuously with N rate increase, and oversupply of N reduced the plantgrowth, leading to a yield decline. This trend was also true for nitrate concentrations in somevegetables and at some sampling times. However, as a whole, the nitrate concentrations in vegetableswere positively correlated with N rates. Thus, addition of N fertilizer to soil was the major causefor increases in nitrate concentrations in vegetables. Nitrate concentrations were much higher inroots, stems and petioles than in blades at any N rate.

Effects of Amino Acids Replacing Nitrate on Growth,Nitrate Accumulation,and Macroelement Concentrations in Pak-choi (Brassica chinensis L.)

A hydroponic experiment was carried out to determine the influence of replacing 20% of nitrate-N in nutrient solutions with 20 individual amino acids on growth, nitrate accumulation, and concentrations of nitrogen （N）, phosphorus （P）, and potassium （K） in pak-choi （Brassica chinensis L.） shoots. When 20% of nitrate-N was replaced with arginine （Arg） compared to the full nitrate treatment, pak-choi shoot fresh and dry weights increased significantly （P ≤ 0.05）, but when 20% of nitrate-N was replaced with alanine （Ala）, valine （Val）, leucine （Leu）, isoleucine （Ile）, proline （Pro）, phenylalanine （Phe）, methionine （Met）, aspartic acid （Asp）, glutamic acid （Glu）, lysine （Lys）, glycine （Gly）, serine （Ser）, threonine （Thr）, cysteine （Cys）, and tyrosine （Tyr）, shoot fresh and dry weights decreased significantly （P ≤ 0.05）. After replacing 20% of nitrate-N with asparagine （Asn） and glutamine （Gin）, shoot fresh and dry weights were unaffected. Compared to the full nitrate treatment, amino acid replacement treatments, except for Cys, Gly, histidine （His）, and Arg, significantly reduced （P ≤0.05） nitrate concentrations in plant shoots. Except for Cys, Leu, Pro, and Met, total N concentrations in plant tissues of the other amino acid treatments significantly increased （P ≤ 0.05）. Amino acids also affected total P and K concentrations, but the effects differed depending on individual amino acids. To improve pak-choi shoot quality, Gln and Asn, due to their insignificant effects on pak-choi growth, their significant reduction in nitrate concentrations, and their increase in macroelement content in plants, may be used to partially replace nitrate-N.

Reducing nitrogen fertilization of intensive kiwifruit orchards decreases nitrate accumulation in soil without compromising crop production

Excessive nitrogen （N） fertilization of high value horticultural crops is a common problem that not only increases the cost to farmers, but also negatively affects crop growth and the environment. A three-year field experiment was conducted in an intensive kiwifruit orchard in Shaanxi Province, China to compare the effects of reduced N fertilization applied as urea （U）, and controlled release urea （CRU） on the N nutrition of kiwi vines, fruit yield and quality, and nitrate-N accumulation in the soil profile. The three treatments included a conventional N application rate （CF-U, 900 kg N ha-1 yr-1 as urea）, two reduced N fertilization treatments where the amount of N fertilizer applied as U and CRU was reduced by 25％ in 2013 and 2014, and by 45％ in 2015. The 25 and 45％ reduced N treatments had no adverse effects on the N concentrations in leaves and pruning branches and the fruit yield and quality of kiwi vines. However, they significantly enhanced the partial factor productivity of applied N （PFPN） and the economic benefits, and reduced nitrate accumulation in the 0-200 cm soil profile. The same benefits of reduced N fertilization were observed for both the U and CRU treatments, but the CRU treatment had the added benefit of decreasing the loss of nitrate through leaching. We concluded that the current level of N fertilization in kiwi orchards is very excessive, and reducing the N fertilizer rate by 25-45％ could not only guarantee fruit yield, but also reduce N accumulation and loss.

Response of Nitrate Metabolism in Seedlings of Oilseed Rape(Brassica napus L.) to Low Oxygen Stress

In order to understand the response of nitrate metabolism in seedlings of oilseed rape （Brassica napus L.） to low oxygen stress （LOS）, two cultivars were studied at different light, LOS time and exogenous nitrate concentrations under hydroponic stress. Results show that N-uptake and dry matter of rape seedlings were decreased after LOS stress while nitrate accumulation （NA） under LOS was induced by darkness. Nitrate accumulation peaked at 3 d while root activity （RA, deifned as dehydrogenase activity） decreased with prolonged waterlogging exposure. Exogenous nitrate signiifcantly elevated NA and RA. Tungstate （TS） and LOS inhibited nitrate reductase （NR） activity while NR transcription and activity were enhanced by exogenous nitrate. Low oxygen stress stimulated the activity of superoxide dismutase （SOD） and peroxidase （POD） slightly, but inhibited that of catalase （CAT）. B. napus L. Zhongshuang 10 （ZS10）, a LOS tolerant cultivar, displayed smaller decrease upon dry matter under LOS, higher NA in darkness and lower NA in light than B. napus L. Ganlan CC （GAC）, a LOS sensitive variety. ZS10 had lower NA and higher RA after waterlogging and exogenous nitrate treatment, and higher NR activity under TS inhibition than GAC, but the activity of antioxidant enzymes did not change under LOS. The results indicate that nitrate metabolism involved tolerance of rape seedlings to LOS, with lower accumulation and higher reduction of nitrate being related to higher LOS tolerance of rape seedlings exposed to waterlogging.

Crop Yield,N Uptake and Nitrates in a Fluvo-Aquic Soil Profile

The effects of different chemical fertilizer combinations (N, P and K) oncrop yield, N uptake and nitrate distribution and accumulation to a depth of 100 cm were studied ina cinnamon fluvo-aquic soil profile (Beijing) with a continuous winter wheat-summer maize croppingsystem for nine years. The experiment consisted of 7 treatments: no fertilizer control (CK); Nalone, N in combination with K (NK), P (NP), and P and K (NPK and N1PK); and P and K in combinationwithout N (PK). The rate of N was 150 kg ha^(-1) for the N treatments except Treatment N1PK withhigher N rate (195 kg ha^(-1)), and the rates of P (P_2O_5) and K (K2O) were 75 and 37.5 kg ha^(-1),respectively. The applications of N combined with P and K (NK, NP and NPK) resulted in higher cropyields than a single application of N. The yields followed the order: NPK > NP > N1PK > PK > NK > N> CK for winter wheat, and NPK > N1PK > NP > NK > N > PK > CK for summer maize. Supplement of N withP or K, or both P and K resulted in a higher average N uptake of the two crops, which was in adecreasing order NPK > NP > N1PK > NK > N > PK > CK. The combinations also increased apparent Nrecovery more than N alone and CK. The nitrate content in the profile was thus reduced more in thecombination treatments. The nitrate accumulation in the soil profiles followed the order: N > NK >N1PK > NPK > NP > CK > PK. Higher N uptake by the adequately fertilized crops (Treatment NPK)reduced nitrate accumulation in the profile and thus reduced nitrate leaching. The optimum N:P:Kratio was thus of paramount importance in increasing yields and N uptake of crops and reducingnitrate leaching losses.

Effect of NH_4^+-N/NO_3^--N Ratios on Growth and Some Physiological Parameters of Chinese Cabbage Cultivars

The responses of three cultivars of Chinese cabbage (Brassica chmensis L.), one of the main vegetable crops in China, to different ratios of NH4+-N/NO3--N was investigated to find the optimal ratio of ammonium to nitrate for maximal growth and to explore ways of decreasing the nitrate content, increasing nitrogen use efficiency of Chinese cabbage, and determining distributions of nitrogen and carbon. Three cultivars of Chinese cabbage were hydroponically grown with three different NH4+-N/NO3--N ratios (0:10…

Effects of residue management and nitrogen fertilizer rates on accumulation of soil residual nitrate and wheat yield under no-tillage system in south-west of Iran

Conservation tillage,residue management and optimizing nitrogen(N)fertilization are important stra-tegies for soil and water conservation and sustainability of agricultural systems.In order to evaluate the effects of various residue management methods and N fertilizer rates on some soil quality indicators,accumulation of residual soil nitrate,and wheat yield under no till system,a split-plot experiment was arranged in a randomized complete block design with three replications.Main plots were three residue management methods,including retaining(R.M1),removing(R.M2)and shredding(R.M3)of corn res-idues.The subplots consisted of four N fertilizer rates,100(N1),150(N2),200(N3),and 250(N4)kg N ha^(-1) from urea source.The results showed that soil organic carbon and total N in R.M1 and R.M3 treatments increased at the depth of 0-15 cm as compared to R.M2.The maximum accumulation of soil nitrate was observed in R.M1 x N4 and R.M3 x N4 interactions at the soil depth of 60-cm.The results of this study showed that R.M1 x N3 and R.M3 x N3 interactions had a greater impact on wheat yield than the sole effect of R.M1 or R.M3.According to our findings,application of 200 kg N ha^(-1) in combination with R.M1 which had once less tractor passing for mechanical shredding than R.M3,can contribute effectively to improve soil quality indicators,control soil residual nitrate and subsequently produce more wheat grain yield in the south-west of Iran.

A putative 6-transmembrane nitrate transporter OsNRT1.1b plays a key role in rice under low nitrogen

OsNRT1.1a is a low-affinity nitrate（NO_3^-） transporter gene. In this study, another mRNA splicing product, OsNRT1.1b,putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a-expressing oocytes accumulated ^（15）N levels to about half as compared to OsNRT1.1bexpressing oocytes. The electrophysiological recording of OsNRT1.1b-expressing oocytes treated with 0.25 mM NO_3^- confirmed ^（15）N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen（N） deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild-type（WT）. The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25 mM NH_4NO_3 and 2.5 mM NO_3^- or NH_4~＋ treatments, but not in 0.125 mM NH_4NO_3.However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125 m M NH_4NO_3,suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.

Effects of autumn plowing on the movement and correlation of moisture,heat and nitrate nitrogen in seasonal freeze-thaw soil

A two-year experiment was established in northern Xinjiang to investigate the effects of autumn plowing methods on nitrate nitrogen accumulation,spring-sown soil conditions and cotton emergence rate,and to explore the response relationship between soil water,heat and nitrate nitrogen.The experiment included five autumn plowing treatments,namely,plough tillage(FG),no-tillage(MG),ridge and furrow alternation(LG),plough tillage with straw mulch(FJ)and plough tillage with activated charcoal mulch(FH).The results showed that both FH and FJ treatments were beneficial to promote the nitrate-nitrogen accumulation in topsoil,while FG,MG and LG treatments aggravated the nitrate nitrogen leaching in topsoil.During the freezing period,FH and FJ treatments were beneficial to reduce soil heat loss and facilitate the coordinated upward migration of soil water and nitrate nitrogen.In the thawing period,FH and FJ treatments favored suppressing the synergistic downward transport of soil water and nitrate-nitrogen and motivated the synergistic upward migration of heat and nitrate nitrogen in deep soil.Binary regression analysis suggested that the interaction between water,heat and nitrate nitrogen under FH and FJ treatments showed a highly significant correlation.FH and FJ treatments showed obvious advantages in regulating soil conditions and optimizing soil water,heat and nitrate nitrogen co-transport mechanism.During the spring sowing period,the FH and FJ treatments increased the average soil temperature by 0.99℃and 1.29℃,and the average soil moisture content by 6.01%and 8.70%,and the average soil nitrate content by 10.20 mg/kg and 10.47 mg/kg,in the 0-25 cm soil layer,respectively.FH and FJ treatments significantly grew the emergence rate of cotton,which can be used as the main autumn tillage strategies in arid areas of northern Xinjiang.