Recovery of fertilizer nitrogen from continuous corn soils under contrasting tillage management

Tillage systems influence soil properties and may influence the availability of applied and mineralized soil N. This laboratory study (20°C) compared N cycling in two soils, a Wooster (fine, loamy Typic Fragiudalf) and a Hoytville (fine, illitic Mollic Epiaqualf) under continuous corn (Zea mays) production since at least 1963 with no-tillage (NT), minimum (CT) and plow tillage (PT) management. Fertilizer was added at the rate of 100 mg ¹⁵N kg^–1–1 soil as 99.9% ¹⁵N as NH₄Cl or Ca(NO₃)₂ and the soils were incubated in leaching columns for 1 week at 34 kPa before being leached periodically with 0.05 M CaCl₂ for 26 weeks. As expected, the majority of the ¹⁵NO₃^– additions were removed from both soils with the first leaching. The majority of applied ¹⁵NH₄⁺ additions were recovered as ¹⁵NO₃^– by week 5, with the NT soils demonstrating faster nitrification rates compared with soils under other tillage practices. For the remaining 22 weeks, only low levels of ¹⁵NO₃^– were leached from the soils regardless of tillage management. In the coarser textured Wooster soils (150 g clay kg^–1), mineralization of native soil N in the fertilized soils was related to the total N content (r² 0.99) and amino acid N (r² 0.99), but N mineralization in the finer textured Hoytville (400 g clay kg^–1) was constant across tillage treatments and not significantly related to soil total N or amino acid N content. The release of native soil N was enhanced by NH₄⁺ or NO₃^– addition compared to the values released by the unfertilized control and exceeded possible pool substitution. The results question the use of incubation N mineralization tests conducted with unfertilized soils as a means for predicting soil N availability for crop N needs.     

Faster anaerobic decomposition of a brittle straw rice mutant: Implications for residue management

Rice (Oryza sativa) in Asia is typically grown on submerged soils in intensive cropping systems with only a brief interval between harvest of one crop and planting of the next. Incorporation of crop residues can be challenging because the fallow period between crops is often too short to allow sufficient decomposition. During early stages of anaerobic residue decomposition in flooded soils, plant growth may be inhibited by nutrient immobilization or by the production of potentially toxic organic acids. Straw from a brittle stem mutant of rice (Oryza sativa L. var. IR68) was tested in a 30-d incubation experiment under continuously flooded conditions in a greenhouse to determine if it would decompose more rapidly than the non-brittle phenotype, thereby allowing shorter fallow time between crops. Brittle straw decomposed faster, as indicated by 51% total C loss as CO₂ or CH₄ within 3 weeks of incorporation, compared with 28% for non-brittle straw. However, brittle straw also produced a significantly higher (P<0.0001) amount of formic, acetic, aconitic, propionic, and butyric acids than non-brittle straw. There was no difference in soil N immobilization pattern between the two straw types, or in P or K availability in the soil, perhaps due to the short duration of the experiment. To maximize the potential advantage of faster decomposition of brittle straw in intensive rice cropping systems, it may be helpful to manage water for sufficient soil aeration to mitigate the negative organic acid and methane production effects.     

Changes in mass and chemistry of plant roots during long-term decomposition on a Chihuahuan Desert watershed

We studied the spatial and temporal patterns of decomposition of roots of a desert sub-shrub, a herbaceous annual, and four species of perennial grasses at several locations on nitrogen fertilized and unfertilized transects on a Chihuahuan Desert watershed for 3.5 years. There were few significant differences between the decomposition rates of roots on the NH₄NO₃ fertilized and unfertilized transects. Decomposition of all roots followed a two-phase pattern: early rapid mass loss followed by a long period of low mass loss. Rates of decomposition were negatively correlated with the initial lignin content of the roots (r=0.90). Mass loss rates of the roots of the herbaceous annual, Baileya multiradiata, were significantly higher than those of the grasses and the shrub, probably as a result of subterranean termites feeding on B. multiradiata root material. The only location where mass loss rates were significantly different was the dry lake bed, where mass loss rates were lower than those recorded on the upper watershed. The spatial differences in mass loss rates in the dry lake were attributable to the high clay content of the soils, which reduced water availability, and to the absence of termites. Non-polar substances in decomposing roots decreased rapidly during the first year, then decreased at a low but fairly constant rate. Water-soluble compounds decreased rapidly (50–60% of initial concentration) during the first 3–6 months. Lignin concentrations of roots of perennial grasses were higher than those of herbaceous annual plants and woody shrubs. Lignin concentrations increased in all species during decomposition. The chemical changes in decomposing roots followed the patterns described for decomposing litter in mesic environments. Received: 20 January 1997     

Denitrification and nitrogen immobilization as affected by organic matter and different forms of nitrogen added to an anaerobic water-sediment system

The effects of wheat straw and different forms of N on denitrification and N immobilization were studied in an anaerobic water-sediment system. The water-sediment system was supplemented with various combinations of wheat straw and ¹⁵N-labelled and unlabelled (NH₄)₂SO₄ or KNO₃, and incubated anaerobically at 30°C for 10 days. ¹⁵N-labelled and unlabelled NO _inf3 ^sup- , NO _inf2 ^sup- , NH _inf4 ^sup+ , and organic N were determined in the water-sediment system. The gases evolved (N₂, CO₂, N₂O, and CH₄) were analyzed by gas chromatography at regular intervals. Larger quantities of ¹⁵N₂–N and organic ¹⁵N were formed in wheat straw-amended systems than in non-amended systems. Trends in CO₂ production were similar to those of N₂–N evolution. The evolution of N₂O and CH₄ was negligible. Denitrification processes accounted for about 22 and 71% of the added ¹⁵NO _inf3 ^sup- –N in the absence and presence of wheat straw, respectively. The corresponding denitrification rates were 3.4 and 12.4 g ¹⁵Ng^-1 dry sediment day^-1. In systems amended with ¹⁵NO _inf3 ^sup- –N and ¹⁵NO _inf3 ^sup- +NH _inf4 ^sup+ –N without wheat straw, 1.82 and 1.58%, respectively, of the added ¹⁵NH _inf3 ^sup- –N was immobilized. The corresponding figures for the same systems supplemented with wheat straw were 5.08 and 4.10%, respectively. Immobilization of ¹⁵NO _inf4 ^sup+ –N was higher than that of ¹⁵NO _inf3 ^sup- –N. The presence of NO _inf3 ^sup- –N did not stimulate NH _inf4 ^sup+ –N immobilization.     

Climatic conditions and crop‐residue quality differentially affect N,P, and S mineralization in soils with contrasting P status

The substitution of the widely practiced crop‐residue burning by residue incorporation in the subtropical zone requires a better understanding of factors determining nutrient mineralization. We examined the effect of three temperature (15°C, 30°C, and 45°C) and two moisture regimes (60% and 90% water‐filled pore space (WFPS)) on the mineralization‐immobilization of N, P, and S from groundnut (Arachis hypogae) and rapeseed (Brassica napus) residues (4 t ha^–1) in two soils with contrasting P fertility. Crop‐residue mineralization was differentially affected by incubation temperature, soil aeration status, and residue quality. Only the application of groundnut residues (low C : nutrient ratios) resulted in a positive net N and P mineralization within 30 days of incubation, while net N and P immobilization was observed with rapeseed residues. Highest N and P mineralization and lowest N and P immobilization occurred at 45°C under nearly saturated soil conditions. Especially net P mineralization was significantly higher in nearly saturated than in aerobic soils. In contrast, S mineralization was more from rapeseed than from groundnut residues and higher in aerobic than in nearly saturated soil. The initial soil P content influenced the mineralization of N and P, which was significantly higher in the soil with a high initial P fertility (18 mg P (kg soil)^–1) than in the soil with low P status (8 mg P (kg soil)^–1). Residue‐S mineralization was not affected by soil P fertility. The findings suggest that climatic conditions (temperature and rainfall‐induced changes in soil aeration status) and residue quality determine N‐ and S‐mineralization rates, while the initial soil P content affects the mineralization of added residue N and P. While the application of high‐quality groundnut residues is likely to improve the N supply to a subsequent summer crop (high temperature) under aerobic and the P supply under anaerobic soil condition, low‐quality residues (rapeseed) may show short‐term benefits only for the S nutrition of a following crop grown in aerobic soil.     

Effect of pH on nitrogen mineralization in crop-residue-treated soils

Summary This study compares N mineralization in soils treated with crop residues [corn (Zea mays L.), soybean (Glycine max (L.) Merr.), sorghum (Sorghum vulgare Pers.)] or alfalfa (Medicago sativa L.) at three adjusted soil pH values (4, 6, and 8); pH was adjusted with dilute H₂SO₄ or KOH. A sample of soil (20 g) was treated with 0.448 g plant material (equivalent to 50t ha^–1), mixed with 20 g silica sand adjusted to the pH of the soil, and packed in a leaching tube. The soil-sand mixture was leached with 100 ml 5 mM CaCl₂ adjusted to the same pH as that of the treated soil to remove the initial mineral N, and incubated at 30°C. The leaching procedure was repeated every 2 weeks for 20 weeks. Results from three soils showed that N mineralization increased as the soil pH increased. In one soil (Lester soil), significant amounts of NH ₄ ⁺ -N accumulated at pH 4 during the first 12 weeks. Treatment with corn and soybean residues resulted in a marked reduction in N mineralization, especially at pH 4. The percentage of organic N mineralized from sorghum residue and alfalfa added to soils increased as the soil pH increased; the values ranged from 7.7% to 37.0% for sorghum and from 17.2% to 30.1% for alfalfa.     

果胶酶的固定化方法研究进展

果胶酶在食品、酿酒、环保、医药及纺织工业上应用十分广泛,固定化果胶酶便于运输和贮存,有利于自动化生产.介绍了几种常用的果胶酶固定化方法,包括吸附法、包埋法、交联法和共价键结合法.     

不同洗涤蜂窝煤灰渣对污染土壤中铅的稳定作用研究

蜂窝煤灰渣具有稳定污染土壤中铅的作用,但可增大土壤pH和电导率（EC）。将蜂窝煤灰渣经过水洗和稀盐酸酸洗后加入铅污染土壤（1 000 mg·kg-1 Pb）,研究了不同处理灰渣对铅有效性和土壤性质的影响。结果表明,灰渣经水洗和酸洗后,其pH（分别下降1.94、3.70）和电导率（0.785、0.890 mS·cm-1）明显下降,重金属有效性和全量也有一定程度的下降。水洗和酸洗灰渣加入土壤后,土壤磷有效性有一定的上升。污染土壤在未加磷条件下加入原灰渣、水洗灰渣和酸洗灰渣后,DTPA-Pb含量分别下降67.2、195、117 mg·kg-1,加磷情况下加入这3种灰渣土壤DTPA-Pb含量分别降低102、91.8、86.8 mg·kg-1,各处理与对照的差异均达到0.05的显著水平。连续提取的结果表明,不同处理对土壤铅形态的影响不明显。     

土壤钝化剂对黑土中铜的原位固定作用

采用盆栽试验研究3种钝化剂(粉煤灰、磷灰石和膨润土)对黑土中铜(Cu)的化学形态、生物积累和有效性的影响。结果表明:3种钝化剂能显著降低Cu污染黑土中水提取态(DW)、TCLP提取态和二乙基三胺五乙酸-三乙醇胺(DTPA-TEA)提取态Cu含量,其中以膨润土的效果最为明显;Tessier连续提取测定发现,3种钝化剂显著降低非残留态Cu(水溶态和交换态、碳酸盐结合态、铁锰氧化物结合态和有机结合态)含量(p<0.01),增加残留态Cu含量,表明3种钝化剂通过改变黑土中Cu的化学形态,降低了黑土中Cu的可淋失性和生物有效性;与对照相比,添加钝化剂能显著降低水稻地上部分的Cu含量(p<0.01),如在400Cu mg/kg处理的土壤上,添加2.5%的粉煤灰、磷灰石和膨润土使米粉中的Cu含量分别降低21.8%,22.7%和31.9%。土壤中可淋失态和生物有效态Cu的分析表明,钝化剂主要是通过改变土壤中Cu的化学形态,降低土壤中Cu的生物有效性,以降低Cu在水稻中的积累;试验表明,Cu污染土壤中施用钝化剂可以修复Cu污染,降低水稻Cu污染风险。     

胰蛋白酶在环氧氯丙烷活化的2%珠状琼脂糖凝胶上固定化条件的研究

用环氧氯丙烷活化 2 %的珠状琼脂糖凝胶 ,并与胰蛋白酶进行偶联反应制备固定化酶。实验结果表明 ,固定化胰蛋白酶的活力受环氧氯丙烷量 ,活化反应的碱浓度及给酶量的影响。每 1.0 g的 2 %珠状琼脂糖凝胶 ,当活化剂量为 5 74 2 μmol,NaOH浓度为 0 .5mol·L-1,活化时间 3h ,给酶量为 5mg·ml-1,偶联 12h时 ,固定化酶活力最大