复合肥的合理选用

复合肥上市已有多年,很多农友们在选择购买时,依然存在一些误区,主要表现在对复合肥的特性及合理选用上。复合肥有许多优点,比如养分种类多,能同时供给作物所需要的多种养分,充分发挥营养元素间相互促进的作用;有效养分高,经济效益明显,在高浓度复合肥料中,有效成分含量至少占30%以上,多数超过40%,有的高达60%。目前我国生产的单质化肥的有效养分平均占20%左右。

Variation of SPAD values in uneven-aged leaves of different dominant species in Castanopsis carlessi forest in Lingshishan National Forest Park

The greenness （SPAD） of uneven-aged leaves of dominant species in the Castanopsis carlessi forest at different altitude gradients in Lingshishan National Forest Park, Fujian Province, China were measured by using portable chlorophyll meter SPAD-502. In addition, the correlation between SPAD value and the concentration of chlorophyll and foliar nitrogen was also investigated. Significant variations in SPAD values were found between the uneven-aged leaves of different dominant species and different altitude gradients. Regression analysis showed that SPAD value was significantly correlated with the concentration of chlorophyll and the content of foliar nitrogen, indicating that SPAD value could be indicators for foliar chlorophyll and nitrogen. It is suggested that SPAD meter is a useful tool for forest assessments in decision-making and operational nutrient management programs.

Effect of Nitrogen on Growth and Yield of Pineapple Grown on BRIS Soil

The physical and chemical properties of BRIS （beach ridges interspersed with swales） soil are unsuitable for agricultural purposes. A proper fertilizer and crop management practices are required. The relationship between different level of nitrogen fertilizer, growth and pineapple fruit yield vary N36 were studied. The experiment was conducted using randomized complete block design of seven treatments with four replicates, Prior to artificial flower induction, seven different rates of nitrogen fertilizer at 0, 200, 400, 600, 800, 1,000 and 1,200 kg-ha^-1 were applied in four equal split doses. As the level of nitrogen fertilizer was increased, a decrease in acidity of fruits and an increase in crown weight were observed. However an increase in mean length of D leaf, mean fruit length, mean fruit weight, mean fruit to crown ratio were obtained as the rate of nitrogen fertilizer was increased from 0-600 kg.N-ha^-1. Further increase however led to a decrease in the same parameters.

Maize （Zea mays L.） Growth and Grain Yield under Conventional and Site-Specific Nitrogen Management in a Dryland Farming System

Large amount of pre-plant nitrogen （N） fertilizer results in low N use efficiency due to poor synchrony between soil N supply and maize N demand, especially during N sensitive growth stages. The objectives of the study were to compare growth and yield of maize （Zea rnays L.） under conventional and site-specific N management in a dryland farming system. The study, which was designed as randomized complete block design was conducted over three site-years under continuous maize cropping system in the semi-arid regions of the Limpopo Province in South Africa. Treatments of the study consisted of three N management strategies on a maize field planted to drought resistant SNK 2147 hybrid maize cultivar. Treatments were： （i） no N application （NO）, （ii） site-specific N at variable rates ranging between 18 kg N/ha and 33 kg N/ha based on soil analysis results （N l） and （iii） conventional and uniform N application broadcasted during planting at 58 kg N/ha （N2）. Sufficiency index as indication of N deficiency was determined using CCM-200 on maize leaves based on leaf numbers during maize vegetative growth stages V6, V10 and Vl4, and thereafter N was applied only when needed. The highest maize grain yield of 5.2 Mg/ha for N 1 was significantly higher （P 〈 0.05） than 3.2 Mg/ha and 4.0 Mg/ha of N0 and N2 in site-year I, respectively. Maize grain yield of 2.2 Mg/ha （Nl） at site-year ll was significantly higher （P _〈 0.05） than 1.7 Mg/ha of the NO. The maize growth and yield under N2 and N1 was compared, N1 required between 43% and 69% lesser N fertilizer as compared to N2 over site-years, and resulted in higher maize height, number of leaves per plant, leaf length, and leaf area than that of conventional N management strategy. Therefore, site-specific N management strategy sustains and improves growth and yield of maize using minimal N fertilizer as compared to conventional approach in low fertility soils of semi-arid regions in dryland farming systems. In examining the results of this study, there was a consistent benefit of site-specific N management strategy on improving growth and yield of maize while saving fertilizer use in small-scale dryland maize farming system.

Oral arginine improves linear growth of long bones and the neuroendocrine mechanism

Objective To investigate the effect of oral administration of arginine on linear growth of long bones in male pubertal rats and the underlying mechanisms, focusing on expression of genes related to the hypothalamus-pituitary growth axis and the nitric oxide （NO）-cyclic guanosine monophosphate （cGMP） pathway. Methods Rats were randomly divided into control and intervention groups. In the intervention group, arginine was solved in water （0.045 g L-arginine was mixed with 1 mL water） and administered in rats （10 mL/kg） through gastric perfusion once per day, for totally 28 d. Rats in the control group received normal saline treatment. Bone histomorphometry analysis was used to measure growth plate width and mineral apposition rate of the tibia, as well as trabecular bone volume fraction, osteoblast surface and osteo- clast surface of the femur. Serum growth hormone （GH） concentration was determined by radioimmunoassay. Real-time PCR was used to measure the expression of neuronal nitric oxide synthase （nNOS）, soluble guanylyl cyclases （sGCal and sGCfll）, growth hormone-releasing hormone （Ghrh） and somatostatin （SS） in hypothalamus, as well as Gh in pituitary. Western blot was used to detect the protein levels ofnNOS, sGCα1 and sGCβ1 in hypothalamus. Results After treat- ment with arginine, the growth plate width of tibia and osteoblast surface of femur were increased （P 〈 0.05）, and serum GH concentration was elevated （P 〈 0.05）. Besides, mRNA and protein levels ofnNOS and sGCα1 （P 〈 0.05）, as well as the expression of Gh mRNA （P 〈 0.01）, were significantly up-regulated, while the expression of SS mRNA was down- regulated （P 〈 0.05）. Conclusion Oral administration ofarginine could improve linear growth of long bones by regulating mRNA expression of SS and Gh and inducing GH secretion, possibly via nNOS-NO-sGC-cGMP signal transduction pathway.

Nutrient resorption and stoichiometric responses of poplar(Populus deltoids)plantations to N addition in a coastal region of eastern China

Aims Leaf nutrient resorption is sensitive to changes in soil nutrients.However,the effects of N deposition on nutrient resorption efficiency(NuRE)in plant macro-nutrients remain unclear.Poplar(Populus deltoids)is one of the most extensively cultivated hardwood species worldwide.We explored general patterns and dominant drivers of NuRE and stoichiometry of poplar plantations in response to N addition.Methods We conducted a 4-year N-addition experiment to explore NuRE and stoichiometric responses to N addition in two poplar(P.deltoids)plantations(8-and 12-year-old stands)in a coastal region of eastern China.We measured soil and foliar(green and senesced leaves)concentrations of nitrogen(N),phosphorus(P),potassium(K),calcium(Ca)and magnesium(Mg)for a series of N addition treatments including N_(0)(0 kg N ha^(−1)yr^(−1)),N_(1)(50 kg N ha^(−1)yr^(−1)),N_(2)(100 kg N ha^(−1)yr^(−1)),N_(3)(150 kg N ha^(−1)yr^(−1))and N_(4)(300 kg N ha^(−1)yr^(−1)).Important Findings Consistent for(both)8-and 12-year-old stands,N addition did not affect the NuRE and stoichiometry(with the exception of CaRE and CaRE:MgRE ratio).N resorption efficiency–P resorption efficiency(NRE–PRE)scaling slopes were consistently less than 1.0 under N addition.These results suggest that NRE generally decouples from PRE within each N treatment.Moreover,these results point to robust control of green leaf nutritional status on nutrient resorption processes as indicated by the positive relationships between NuRE and green leaf nutrient concentrations.Our findings provided a direct evidence that growth in 12-year-old poplar plantations was N-limited in the coastal region of eastern China.

Site-Specific Nitrogen Management in Dry Direct-Seeded Rice Using Chlorophyll Meter and Leaf Colour Chart

The need to maintain high rice yields and improve fertilizer nitrogen(N)-use efficiency has fueled the use of tools such as leaf colour chart(LCC) and chlorophyll meter(SPAD meter) in managing fertilizer N based on colour of the leaf. Field experiments were conducted during 2011 to 2013 at Ludhiana, India to assess the need for basal N application and to establish critical threshold values of leaf greenness as measured by LCC and SPAD meter for formulating strategies for in-season management of fertilizer N in dry direct-seeded rice(DDSR). Avoiding application of N at sowing did not adversely affect rice grain yield, indicating that basal N application in DDSR was not necessary and might lead to reduced N-use efficiency. Monitoring N uptake rate during the growing season of DDSR suggested that N uptake rate peaked at the two growth stages: maximum tillering(42 to 56 days after sowing(DAS))and panicle initiation stages(70 to 84 DAS). Using the Cate-Nelson procedure, critical LCC and SPAD meter values for fertilizer N application worked out to be 4 and 37, respectively. Real-time fertilizer N management strategy based on applying 30 kg N ha-1whenever SPAD meter or LCC readings fell below the critical values maintained optimum rice yields along with higher N-use efficiency than that observed by following blanket recommendation for fertilizer N in the region. The fixed-time variable-dose strategy consisted of applying prescriptive doses of 20 kg N ha-1at 14 DAS and 30 kg N ha-1at 28 DAS and corrective doses of 30, 40 or 50 kg N ha-1at 49 and 70 DAS depending upon LCC shade to be ≥ 4, 4–3.5, or < 3.5 and SPAD meter readings to be ≥ 40, 40–35, or< 35, respectively. This strategy also resulted in optimal rice yield along with higher N-use efficiency as compared to the blanket recommendation. This study revealed that in DDSR, fertilizer N could be managed more efficiently using the tools of LCC and SPAD meter than the current blanket recommendation.