Nitrogen behavior in tropical wetland rice soils. 2. The efficiency of fertilizer nitrogen,priming effect and A-values

Results of tracer pot experiments show that in tropical wetland rice soils, rice plants recovered 50–69% of applied fertilizer N in the first cropping, 7–12% in the second cropping and 1–4% in the third cropping. Recovery of fertilizer N in the presence of incorporated rice straw was decreased to 45–53% (first cropping), 9–12% (second cropping), and 3–5% (third cropping), respectively. Application of fertilizer N resulted in the increase in plant uptake of native soil nitrogen due to priming effect which valued 3–29% of total N uptake by the rice plants. A-values calculated show overestimated amounts of available soil N in relation to plant uptake of native soil N. Perhaps their use in assessing fertilizer requirement in tropical wetland rice soils would be of limited meaning.     

Genotypic differences and some associated plant traits in potassium internal use efficiency of lowland rice (Oryza sativa L.)

As potassium (K) deficiency in paddy soils is becoming one of the limiting factors for increasing rice yield in Asia, it is important to identify genotypic differences and exploit genetic potential for K use efficiency in lowland rice. Successful identification of K-efficient genotypes and genetic improvement largely depend on development of accurate and feasible screening parameters and methods. In this study, over 134 rice (Oryza sativa L.) genotypes were tested under nutrient solution and field conditions at low and adequate K levels to examine genotypic differences in K internal use efficiency (KIUE) and identify the associated plant traits. Marked differences in K internal use efficiency for biomass production (KIUE-B) and for grain production (KIUE-G) were observed among the rice genotypes. The KIUE-B at the seedling stage (g DW g^–1 K taken up) differed sixfold among the 134 rice genotypes under low K. A positive and close correlation was observed between the relative shoot and root dry matter yields, relative root K accumulation and the KIUE-B at the seedling stage, respectively. However, a negative and significant correlation was found between the KIUE-B and the relative K concentrations in shoots and roots, and the relative K accumulation in shoots, respectively. The results from the two years of field experiments showed that rice genotypes with greater KIUE-B at the seedling stage had higher KIUE-B at the tillering stage and higher KIUE-G at physiological maturity. Both KIUE-B at the tillering stage and KIUE-G at physiological maturity were closely and positively correlated with the relative shoot dry matter yield in shoots at the tillering stage and harvest index under low K, and had a highly significant and negative correlation with the shoot K concentration and accumulation at low K among the nine rice genotypes. Therefore, the K internal use efficiency could be used as an index for selecting K-efficient genotypes. The relative shoot biomass, relative root length, K concentration and accumulation in shoots as well as harvest index are among the most important plant traits for identifying K-efficient genotypes in lowland rice.     

复混肥料中总氮含量检验技术及常见问题解析

通过对复混肥料中不同形态氮的化学性质的分析,解答了复混肥料总氮含量检验中的常见问题。提出了氮形态的定性鉴定法和检验关键点,旨在对复混肥的检验工作有所帮助。     

Influence of straw mulching on fertilizer nitrogen use efficiency,moisture conservation and herb and essential oil yield in Japanese mint (Mentha arvensis L.)

In a field study, the influence of organic mulches viz. paddy straw and citronella (Cymbopogon winterianus Jowitt) distillation waste on herb and essential oil yield and fertilizer N use efficiency in Japanese mint (Mentha arvensis L.) were examined for two years. Herb yield (dry weight) increased by 17 and 31% with paddy straw and citronella distillation waste, respectively over the use of no mulch. Essential oil yield also significantly increased due to mulching. A significant response to N was observed with 200 kg N ha^–1 in unmulched plots as against 150 kg N ha^–1 in mulched plots. Mulched soils have been observed to contain 2 to 4% higher moisture as compared to unmulched soils. Nitrogen uptake by plants increased by 18 and 25% over no mulch with using paddy straw and citronella distillation waste, respectively.     

Effect of irrigation and nitrogen fertilizer on yield,oil content,nitrogen accumulation and water use of canola (Brassica napus L.)

Effects of N application and water supply on yield, oil content and N accumulation by canola, cultivar Marnoo, grown on a heavy clay soil in the Goulburn Murray Irrigation Region were investigated. Treatments were rainfed (R_f) or watered at a deficit of 50 mm (40–60 mm, I₅₀) beginning in the spring. N treatments were 0, 50, 100 or 200 kg N ha^–1 at sowing or as split applications of 20/80, and 50/50 kg N ha^–1 at sowing and rosette, respectively.Yield (Y_g) ranged from 170 to 520 g m^–2. Irrigation and N increased yield in both years. Grain yields were increased by N application on the irrigated treatments when 100 or 200 kg N ha^–1 was applied. Oil concentrations ranged from a maximum of 46.4% in treatment N₀ to a minimum of 40.6% in treatment N₂₀₀ and was inversely related to seed N concentration. Although fertilizer N decreased oil concentration, it increased the yield of oil.Nitrogen accumulation (N_b) limited yield of all treatments and was described by the equation, Y_g = 806[1-EXP(–0.039*N_b)]. This implied a decrease in yield per unit of N_b at the higher rates of fertilizer addition with consequent increases in grain N concentration.The efficiency of water use in the production of grain (WUE_g) and biomass (WUE_b) were 7.5 and 23 kg ha^–1 mm^–1 respectively. Nitrogen additions increased WUE_g and WUE_b in both seasons. Maximum values of 8.9 (WUE_g 1986) and 26.8 (WUE_b 1987) were measured from treatment N₂₀₀. These data suggest that the crops made efficient use of the applied water.     

Effect of fertilization on organic and microbial biomass nitrogen using15N under corn (Zea mays L.) in two Quebec soils

Changes in soil organic N following fertilizer N applications are related to soil quality and subsequent N uptake by plants. Recovery of fertilizer N as organic N and soil microbial biomass N within two corn (Zea mays L.) fertilization systems was studied using¹⁵N on a Chicot soil (fine-loamy, mixed, frigid, Typic Hapludalf) and a Ste. Rosalie soil (fine, mixed, frigid, Typic Humanquept) in southwestern Quebec in 1989 and 1990. The two fertilization systems studied received a recommended rate of 170-44-131 kg (normal rate) and a high rate of 400-132-332 kg of N-P-K per hectare. Increasing fertilization rates above normal increased microbial biomass N immobilization with a subsequent greater N release. Higher fertilization rates significantly increased both the magnitude of soil microbial biomass N and microbial fertilizer N recovery in the soil microbial biomass.     

The influence of rate and time of nitrate supply on nitrogen fixation and yield in pea (Pisum sativum L.)

The influence of nitrate N supply on dry matter production, N content and symbiotic nitrogen fixation in soil-grown pea (Pisum sativum L.) was studied in a pot experiment by means of¹⁵N fertilizer dilution. In pea receiving no fertilizer N symbiotic nitrogen fixation, soil and seed-borne N contributed with 82, 13 and 5% of total plant N, respectively. The supply of low rates of nitrate fertilizer at sowing (starter N) increased the vegetative dry matter production, but not the seed yield significantly. Nitrogen fixation was not significantly decreased by the lower rates of nitrate but higher rates supplied at sowing reduced the nitrogen fixation considerably. Applying nitrate N at the flat pod growth stage increased the yield of seed dry matter and N about 30% compared to pea receiving no nitrate fertilizer. Symbiotic nitrogen fixation was reduced only about 11%, compared with unfertilized pea, by the lowest rate of nitrate at this application time. The pea very efficiently took up and assimilated the nitrate N supplied. The average fertilizer N recovery was 82%. The later the N was supplied the more efficiently it was recovered. When nitrate was supplied at the flat pod growth stage 88% was recovered, and 90% of this N was located in the seeds.     

Response of rainfed bread and durum wheat to source,level and timing of nitrogen fertilizer on two Ethiopian Vertisols: II. N uptake,recovery and efficiency

In trials conducted at 2 highland Vertisol sites in Ethiopia in 1990 and 1991, 2 locally popular wheat cultivars, 1 spring bread wheat (Triticum aestivum L.) and 1 durum wheat (T. durum Desf.), were supplied with nitrogen (N) fertilizer at 0, 60 and 120 kg N ha^–1 in the form of large granular urea (LGU), standard urea prills or ammonium sulfate. N was applied all at sowing, all at mid-tillering or split-applied between these two stages (1/3:2/3). While durum wheat exhibited the highest N concentration in grain and straw, bread wheat, because of its higher productivity, resulted in a greater grain and total N uptake. In general, split application of N and use of LGU as N source enhanced grain and total N uptake, apparent N recovery and agronomic efficiency of N, particularly under severe water-logging stress. Where significant, the interactions among the experimental factors substantiated the superior responsiveness of the bread wheat cultivar to fertilizer N, and the beneficial effects of split N application and LGU as an N source. Split application of N tended to nullify the positive effects of LGU, presumably by approximating the delayed release of N achieved with LGU. Considering the potential benefits to Ethiopian peasant farmers and consumers, split application of N should be advocated, particularly on water-logged Vertisols; LGU could be an advantageous N source assuming a cost comparable to the conventional N source urea.     

The effect of nitrogen,phosphorus and potassium fertilizer applications on the seed yield of sunflower (Helianthus annuus L.) grown on sandy soils and the prediction of phosphorus and potassium responses by soil tests

The nitrogen, phosphorus and potassium requirement of sunflower was evaluated when the crop was grown on siliceous sands overlying clay in the south east of South Australia. Of the seven sites used in the investigation, significant seed yield responses to phosphorus were recorded at two, while at a further two sites seed yields were increased by potassium additions. Nitrogen applications did not significantly increase seed yields at any site but decreased seed yields at two. This lack of nitrogen response was attributed to the sites having been long term legume pastures prior to the sunflower crops.Oil concentrations of sunflower seed ranged from 40.6% to 45.3% between sites, but fertilizer treatment had no significant effect.Critical nutrient ranges for both soil (Colwell) extractable phosphorus and potassium were derived at maximum seed yield. These were 16–20 mg kg^–1 for extractable phosphorus and 70–80 mg kg^–1 for extractable potassium.     

Effect of nitrogen,phosphorus and soil and crop residues management practices on maize (Zea mays L.) yield in ultisol of eastern Cameroon

The shortening of fallow period in several areas in tropical Africa has reduced soil fertility and exposed soils to erosion and run-off. Fertilizer application and crop conservation practices are needeed to sustain high crop yield and to conserve the natural resource base for upland crop production in the continent. Field trials were carried out to evaluate the effect of fertilizer application and soil and crop residues management practices on yield of maize (Zea mays L.) planted on a Plinthudult soil at Bertoua, Eastern Cameroon. Maize yields increased significantly with nitrogen and phosphorus fertilizer application. Under the rainfall pattern prevailing in the area, the amount of nitrogen required for maximum yield was higher in the second season. On the other hand, the amount of phosphorus required for maximum yield appeared to decrease with time. The burning of crop residues and weeds prior to planting together with no-till practive gave higher yield of maize than other soil and crop residues management practices.     

The influence of potassium supply on nodulation,nitrogenase activity and nitrogen accumulation of soybean (Glycine max L. Merrill) grown in nutrient solution

The influence of potassium nutrition on dry matter yield, nodulation, N accumulation and nitrogenase activity of soybean were studied under controlled conditions in hydrophonic and sand culture at 4 levels of K in a nutrient medium (1.0, 5.0, 10.0 and 20.0 mM). The dry matter yield, nodule parameters (nodule number and fresh weight of nodule per plant, average weight of nodule) and total nitrogen accumulation in the plant increased with increasing K-supply. The lowest potassium level, 1.0 mM was suboptimal for normal growth, nodulation and N -accumulation, whereas 5.0 mM K was found to be an optimal level for these same parameters. However, the nitrogenase activity, which was determined non-destructively, was not affected by an increased supply of K.     

Presence of a hydroxamic acid glucoside in wheat phloem sap,and its consequences for performance ofRhopalosiphum padi (L.) (Homoptera: Aphididae)

Phloem sap of wheat seedlings differing in whole leaf hydroxamic acid (Hx) concentrations was collected by cutting stylets of feeding aphids. DIMBOA-glucoside was the only Hx-related product found. Concentration of DIMBOA-glucoside in phloem sap showed a tendency to be negatively correlated with aphid performance.     

Phosphorus seed coating increases phosphorus uptake,early growth and yield of pearl millet (Pennisetum glaucum (L.) R. Br.) grown on an acid sandy soil in Niger,West Africa

In pot and field experiments conducted in 1990 and 1991 on an acid sandy, phosphorus (P) deficient soil in Niger, West Africa, the effect of seed coating on seedling emergence, early growth and grain yield of pearl millet (Pennisetum glaucum (L.) R. Br.) was studied. Seeds of pearl millet were coated with different rates (0; 0.5; 1.0; 2.0; 5.0; 10.0 mg P seed^–1) and types of P fertilizers (single superphosphate, ammonium dihydrogen phosphate; monocalcium phosphate, sodium dihydrogen phosphate and sodium triphosphate). Seedling emergence was generally reduced at coating rates higher than 0.5 mg P seed^–1 and prevented with single superphosphate and sodium triphosphate at rates higher than 5 mg P seed^–1. No correlation was found between the pH and osmomolity of the coatings and final emergence of millet seedlings. The most favourable effect on plant growth and P content was achieved with ammonium dihydrogen phosphate (AHP) as seed coating. This was attributed to the enhancement effect of ammonium on P uptake. Compared to the untreated control dry matter production at 20 days after planting (DAP) was increased by 280%, P content per plant by 330%, total biomass at maturity by 30% and grain yield by 45%. Although seed coating with AHP may be harmful to seedlings emergence, it represents a suitable method to enhance early growth and increase yield of pearl millet.