Crop residue chemistry,decomposition rates,and CO<Subscript>2</Subscript> evolution in Bt and non-Bt corn agroecosystems in North America: a review

Corn (Zea mays L.) is a major cereal crop, with production on more than one-fifth of the agricultural land worldwide. In North America, about 50% of corn acreage is planted with transgenic corn hybrids such as those with the gene from Bacillus thuringiensis (Bt) that express the insecticidal crystalline protein (Cry1Ab) for the control of European corn borer (ECB, Ostrinia nubilalis Hubner). Widespread production of Bt corn could affect soil organic carbon (SOC) storage in agroecosystems if transgenic corn differs from conventional corn in yield and chemical composition. Generally, the yield of Bt corn is greater than non-Bt corn in years when there is severe infestation of corn insect pests. Some authors report that Bt corn has higher lignin content than non-Bt corn, whereas others found no difference in the chemical composition of near isolines. Residues with higher lignin content are expected to have a slower decomposition rate and release less CO₂ to the atmosphere; however, this is not supported by the literature. A few studies have examined decomposition of Bt corn residues in this context, and the findings to date have been inconclusive, perhaps due to the variety of experimental approaches used to study this question. Generally, the literature supports the view that decomposition rates in Bt corn- and non-Bt corn-amended soils are similar. Whether Bt corn has greater lignin content or slower decomposition rates, the relevant question is whether this will affect the amount of C storage in the soil. A significant gain in SOC requires crop residue inputs with higher lignin content than what is realistically expected from Bt corn residue.     

Differences in Yields,Residue Composition and N Mineralization Dynamics of Bt and Non-Bt Maize

Cultivation of genetically modified crops may have several direct and indirect effects on soil ecosystem processes, such as soil nitrogen (N) transformations. Field studies were initiated in Northeast Missouri in 2002 and 2003 to determine grain and biomass yields and the effects of application of crop residues from five Bt maize hybrids and their respective non-Bt isolines on soil inorganic N under tilled and no-till conditions in a maize-soybean rotation. A separate aerobic incubation study examined soil N mineralization from residue components (leaves, stems, roots) of one Bt maize hybrid and its non-Bt isoline in soils of varying soil textural class. Three Bt maize hybrids produced 13–23% greater grain yields than the non-Bt isolines. Generally no differences in leaf and stem tissues composition and biomass was observed between Bt and non-Bt maize varieties. Additionally, no differences were observed in cumulative N mineralization from Bt and non-Bt maize residues, except for non-Bt maize roots that mineralized 2.7 times more N than Bt maize roots in silt loam soil. Incorporation of Bt residues in the field did not significantly affect soil inorganic N under tilled or no-till conditions. Overall Bt and non-Bt maize residues did not differ in their effect on N dynamics in laboratory and field studies.     

Effects of Genetic Modification on Herbivore-Induced Volatiles from Maize

Large-scale implementation of transgenic crop varieties raises concerns about possible nontarget effects on other organisms. This study examines the effects of genetic modification on plant volatile production and its potential impact on arthropod population dynamics. We compared herbivore-induced volatile emissions from Bacillus thuringiensis Berliner (Bt) maize plants to those from a nontransformed isoline following exposure to various types of leaf damage. When equal numbers of Helicoverpa zea Boddie (Lepidoptera: Noctuidae) larvae fed on Bt and non-Bt maize, volatile emissions were significantly lower in the transgenic plants, which also exhibited less leaf damage. When damage levels were controlled by adding more larvae to Bt plants, the plants' volatile emissions increased but displayed significant differences from those of nontransgenic plants. Significantly higher amounts of linalool, β-myrcene, and geranyl acetate were released from transgenic maize than from non-Bt plants. Manipulating the duration of feeding by individual larvae to produce similar damage patterns resulted in similar volatile profiles for Bt and non-Bt plants. Controlling damage levels more precisely by mechanically wounding leaves and applying larval regurgitant likewise resulted in similar emission patterns for Bt and non-Bt maize. Overall, changes in the herbivore-induced volatile profiles of Bt maize appeared to be a consequence of altered larval feeding behavior rather than of changes in biochemical plant defense pathways. The implications of these findings for understanding the impacts of plant-mediated cues on pest and natural enemy behavior in transgenic crop systems are discussed.     

Densification characteristics of corn cobs

Corn cobs are potential feedstocks for producing heat, power, fuels, and chemicals. Densification of corn cobs into briquettes/pellets would improve their bulk handling, transportation, and storage properties. In this study, densification characteristics of corn cobs were studied using a uniaxial piston-cylinder densification apparatus. With a maximum compression pressure of 150 MPa, effects of particle size (0.85 and 2.81 mm), moisture content (10 and 20% w.b.), and preheating temperature (25 and 85 °C) on the density and durability of the corn cob briquettes (with diameter of about 19.0 mm) were studied. It was found that the durability (measured using ASABE tumbling can method) of corn cob briquettes made at 25 °C was 0%. At both particle sizes, preheating of corn cob grinds with about 10% (w.b.) moisture content to 85 °C produced briquettes with a unit density of > 1100 kg m^-3 and durability of about 90%.     

木质纤维素甲酸预处理及其组分分离

以玉米芯为研究对象,提出了常压中温条件下甲酸预处理木质纤维素组分分离的工艺. 在该体系中半纤维素迅速发生水解,大部分木质素被溶解,而纤维素基本不发生水解,经固液分离和甲酸回收实现了玉米芯全组分分离. 考察了预处理温度、时间和甲酸浓度对玉米芯各组分分离效果及水解产物(可溶性糖)含量的影响规律,结果表明,随着反应的进行,甲酸溶液中可溶性糖和木质素量先迅速增大,随后趋于平衡;在50~75℃间对各组分分离的影响不明显. 综合考虑分离效果和成本,选择最佳反应温度为60℃,处理时间为3 h,甲酸浓度为88%(w). 在该条件下,纤维素、半纤维素和木质素回收率分别可达91.4%, 88.5%和63.7%.     

Nitrogen contributions from decomposing cover crop residues to maize in a tropical derived savanna

In cover cropping systems in the tropics with herbaceous legumes, plant residues are expected to supply nitrogen (N) to non-legume crops during decomposition. Field experiments were carried out to (i) determine the effects of residue quality on decomposition and N release patterns of selected plants in cover cropping systems, (ii) relate the pattern of residue N release to N uptake by maize in cover cropping systems. To study decomposition, litter bags were used and monitored over two maize growing seasons. The residues studied were mucuna (Mucuna pruriens (L.) DC. var. utilis (Wright) Bruck), lablab (Lablab purpureus (L.) Sweet), and leaves and rhizomes of imperata (Imperata cylindrica (L.) Raueschel). Mucuna and lablab decomposed rapidly losing more than 60% of their dry weight within 28 days. In contrast, imperata decomposed slowly with only 25% of its dry matter lost in 56 days. At 28 days, mucuna had released 154 kg N ha^-1 in in-situ mulch systems and 87 kg N ha^-1 in live- mulch systems representing more than 50% of its N. More than 64% of N in lablab was released within 28 days amounting to 21 to 174 kg N ha^-1. Imperata rhizomes mineralized 4 to 14 kg N ha^-1 within 14 days, and subsequently immobilized N until 112 days whereas imperata leaves immobilized N throughout the study period. Decomposition and N release rates from the plant residues were most strongly correlated with the (lignin+polyphenol)/N ratio, N content, lignin/N ratio, polyphenol/N ratio, C/N ratio and lignin content of the residues. Relative to the controls, herbaceous legume residues increased maize dry matter yield and N uptake during the two cropping seasons. At 84 days, the maize crop had utilized 13 to 63 kg N ha^-1from mucuna representing 13 to 36% of N released, whereas 16 to 25% of N released from mucuna was recovered by the maize crop at 168 days. The first maize crop recovered 9 to 62 kg N ha^-1 or 28 to 35% of N released from lablab. However, at 168 days, N uptake by maize in antecedent live-mulched lablab was 32% higher than the quantity of N released, whereas imperata residues generally, resulted in net reduction of maize N uptake.     

Super sweet corn hybrids adaptability for industrial processing. I freezing

With the purpose of evaluating adaptability to the freezing process of super sweet corn sh2 hybrids Krispy King, Victor and 324, 100 cobs of each type were frozen at -18 degrees C. After 120 days of storage, their chemical, microbiological and sensorial characteristics were compared with a sweet corn su. Industrial quality of the process of freezing and length and number of rows in cobs were also determined. Results revealed yields above 60% in frozen corns. Length and number of rows in cobs were acceptable. Most of the chemical characteristics of super sweet hybrids were not different from the sweet corn assayed at the 5% significance level. Moisture content and soluble solids of hybrid Victor, as well as total sugars of hybrid 324 were statistically different. All sh2 corns had higher pH values. During freezing, soluble solids concentration, sugars and acids decreased whereas pH increased. Frozen cobs exhibited acceptable microbiological rank, with low activities of mesophiles and total coliforms, absence of psychrophiles and fecal coliforms, and an appreciable amount of molds. In conclusion, sh2 hybrids adapted with no problems to the freezing process, they had lower contents of soluble solids and higher contents of total sugars, which almost doubled the amount of su corn; flavor, texture, sweetness and appearance of kernels were also better. Hybrid Victor was preferred by the evaluating panel and had an outstanding performance due to its yield and sensorial characteristics.     

Potential use of different agroindustrial by-products as supports for fungal ellagitannase production under solid-state fermentation

Ellagitannase is a novel enzyme responsible for biodegradation of ellagitannins and ellagic acid production. Ellagic acid is a bioactive compound with great potential in food, pharmaceutical and cosmetic industries. This work describes the ellagitannase enzyme production from partial purified ellagitannins as inducers by Aspergillus niger GH1 grown on solid-state fermentation. Solid-state fermentation was carried out on four different lignocellulosic materials (sugarcane bagasse, corn cobs, coconut husks and candelilla stalks) as matrix support and production of ellagitannase enzyme was evaluated. All lignocellulosic materials were characterized in terms of water absorption index and critical humidity point. The best lignocellulosic materials for ellagitannase production were sugarcane bagasse and corn cobs (1400 U L⁻¹ and 1200 U L⁻¹, respectively). The lowest values were obtained with candelilla stalks (500 UL-1). The highest specific productivity was obtained with corn cobs (2.5 U mg⁻¹ h⁻¹) which enable increase ellagitannase productivity up to 140 times. Corn cobs have great potential as support matrix for production of fungal ellagitannase in SSF.     

Production and in vitro evaluation of xylooligosaccharides generated from corn cobs

Corn cobs are major byproduct of maize processing industries. For value addition of maize byproducts, the present paper aims at extracting xylan from corn cobs and subsequent production of xylooligosaccharides (XOS). Compositional determination of corn cobs revealed 38.78% hemicellulose, 27.71% cellulose and 9.4% lignin. Recovery of xylan increased with increasing concentration of alkali during extraction. The extracted xylan was subjected to acidic hydrolysis to yield XOS. HPLC analysis of hydrolysate revealed increased production of XOS with time, but prolonged incubation resulted in higher amount of xylose. Four probiotic strains were used for undertaking in vitro evaluation of the prebiotic efficacy of XOS. XOS ensured higher growth rate for Enterococcus faecium as compared to other probionts, while fructooligosaccharides (FOS) supported higher proliferation of Lactobacillus viridiscens. This method of xylan extraction and production of XOS offers scope for value addition to the corn byproducts.     

How does plant leaf senescence of grassland species influence decomposition kinetics and litter compounds dynamics?

The influence of litter quality on plant litter decomposition rates is a crucial aspect of the soils C cycle. In grassland ecosystems, leaf litter, which is not removed either by herbivores or by mowing, returns to soil after the senescence process (brown litter). In grassland managed by mowing, another significant proportion of litter returns to the soil before senescence through harvesting losses (green litter). We hypothesized that changes in leaf tissue quality due to the senescence process would lead to contrasting decomposition dynamics of brown litter compared to green litter. Our conceptual approach included the monitoring of decomposition of green (fresh leaves) and brown litter (dead leaves, still attached to the plant) of three different grassland species (Lolium perenne, Festuca arundinacea and Dactylis glomerata) during a 1 year field incubation. After 0, 2, 4, 20 and 44 weeks, we retrieved the litterbags and analysed the remaining material for carbon and nitrogen content and stable isotope composition. Additionally, we determined the lignin content and composition by CuO oxidation and the non-cellulosic neutral carbohydrate content and composition after TFA hydrolysis. As expected, green litter, being higher in N and soluble compounds, while showing a lower C:N ratio and lower lignin contents compared to brown litter, was degraded at a higher rate. Carbon decomposition kinetics suggests that both leaf litter types consist of two pools with contrasting turnover times. The size of the active pool was related to the initial content of soluble plant litter compounds and the size of the recalcitrant pool was related to the lignin to N ratio of initial plant material. More lignin was lost from green litter compared to brown litter. P-coumaryl-type lignin units were decomposed at a higher rate than vanillyl and syringyl units. Total non cellulosic polysaccharide content showed little changes for both litter types. In contrast, the ratios of hexoses/pentoses (C6/C5) and desoxy sugars/pentoses (desoxy/C5) increased during decomposition of green litter only. This is an indication for an increasing contribution of microbial derived compounds being consistant with the higher decomposition rate of this material. Our results showed that grassland management (grazing versus mowing) could influence soil carbon sequestration through different proportions of green and brown litter returned to soil.     

Characterization of protein extracted from flaked,defatted, whole corn by the sequential extraction process

An investigation was conducted to identify and characterize protein extracted by 45% ethanol:55% 0.1 M NaOH from flaked, defatted, undegermed corn (Zea mays L.) during Sequential Extraction Processing (SEP). This new approach to corn milling, SEP, recycles the ethanol produced from the fermentation of cornstarch to upstream steps of protein extraction and the simultaneous extraction of corn oil and dehydration of the ethanol. About 10% of the protein was extracted by ethanol during counter-current-percolation oil extraction. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and amino acid analysis identified this protein as zein. Nearly 65% of the total protein was recovered by the process in the protein extraction step from soft dent corn (Pioneer 3377), medium-hard dent corn (Pioneer 3732) and high-lysine corn. The freeze-dried solids of the ethanol/alkali extracts from these corn hybrids contained about 80% crude protein (db). The amino acids were present in quantities similar to those in whole corn and markedly higher than those in corn gluten meal. These results indicate that SEP produces high-quality protein suitable for food and industrial uses. Paper presented at the Symposium on Oilseed Processing for Edible Food and Feed Products, 82nd Annual Meeting of the AOCS, May 12–15, 1991. Research Associate, Assistant Professor, and Professor, respectively.     

Adsorption of methane on corn cobs based activated carbon

Activated carbon was prepared with corn cobs and potassium hydroxide under optimized variables. Due to their botanical origin, corn cobs can be an excellent starting material to produce nanoporous carbon for natural gas storage. Samples with different BET surface areas were chosen to perform methane adsorption experiments. Methane adsorptions on corn cob based activated carbon were studied at four different pressures (500, 1000, 1500 and 2000 psi) and two different temperatures (298 K and 323 K) in a volumetric adsorption apparatus. The volume based methane adsorption results specified an ‘increase in the methane adsorption capacities of activated carbon with increasing surface area and showed that adsorption capacity of methane depends on pressure and temperature. The highest methane storage capacity was found to be 160 (v/v) at 298 K and 1500 psi. The applications include use in the transportation of natural gas, natural gas based vehicles, and adsorption of gas from landfills.     

Impact of lignin extraction methods on microstructure and mechanical properties of lignin‐based carbon fibers

In order to optimize the use of residues of enzymatic hydrolysis of corn stalk (REHCS) and explore the low‐cost and sustainable raw material substitute for carbon fibers, three types of lignin samples were extracted from REHCS by various extraction methods, and then they were converted into carbon fibers (CFs) by electrospinning, thermostabilization, and carbonization under the same process conditions. The microstructure and mechanical properties of the three types of carbonized fibers were different. The CFs from the ethanol organosolv lignin were actually smooth and brittle carbon films. The CFs from the formic acid/acetic acid organosolv lignin had microscopic pores, causing poor mechanical properties. Comparatively, the CFs from the alkaline lignin demonstrated preferable microstructure and mechanical properties. The reasons for the differences were analyzed by characterizing the lignin samples, precursor fibers, and resultant CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45580.     

EFFECTS OF HYBRID AND DAMAGE ON MOLD DEVELOPMENT DURING LOW TEMPERATURE DRYING AND STORAGE OF HIGH MOISTURE SHELLED CORN

Several corn hybrids either resistant or susceptible to storage mold were harvested with a combine and stored at high moistures (19 to 24% moisture, wet basis) in 0.81 m³ (23 bu) bins nd in “mini-bins” containing 1200 g (2.6 lbs). For several hybrids, two damage levels were achieved by adjusting combine cylinder speed. Storage conditions were the same as those found in a low temperature drying bin. Mold growth in the bins and “mini-bins” was monitored by determining number of propagules, percent seeds fine material was removed from all hybrids tested in 1986, whereas in 1985 it was not removed. This probably improved the storability of the 198 6 corn and reduced the differences in mold invasion. Furthermore, the sporulation and growth of mold were lower and differences may not have had time to develop.

Bin and small scale tests were consistent in differentiating the relative resistance of hybrids and they agreed with results of laboratory studies (Friday, 19,87). Some of the observed differences can be attributed to physical damage. However, there was an incremental decrease in storability above that which could be explained by damage, which the authors believe was caused by the hybrid effect. FRB73 × Mol7 was consistently more resistant to storage molds than the other hybrids tested. FRB73 × Mol7 and FR35 × FR20 displayed a higher level of mold resistance in all storage tests while P3707 and P3377 were consistently more susceptible. (Authors note: not all Pioneer hybrids are more susceptible to storage molds as some Pioneer hybrids have been found to store well in laboratory tests.)

The agreement of the bin, small scale, and laboratory studies suggests that hybrids can be screened for mold resistance in the laboratory. Hopefully, this will encourage plant breeders to begin such screening. This would be even more feasible if the laboratory procedures could be simplified and if the incubation time prior to evaluation for mold invasion could be reduced.     

Parametric studies on catalytic pyrolysis of coal-biomass mixture in a circulating fluidized bed

Pyrolysis is an efficient way of thermally converting biomass into fuel gas, liquid product and char. In this research, pyrolysis experiments were carried out in a circulating fluidized bed reactor with a riser diameter of 25 mm and height 1.65 m. The biomass used was corn cobs. The experiments were conducted systematically using two level factorial design with temperature ranging from 650 to 850 degree Celsius, corn cobs and catalyst contents in feed ranging from 0 to 100%, and from 1 to 5 wt%, respectively, and Ni loaded on catalyst ranging from 5 to 9 wt%. The results showed that when temperature and catalyst contents in feed and Ni loaded on catalyst increased, the percent of hydrogen and carbon monoxide increased. The amount of corn cobs was found to have an effect only on the composition of hydrogen. Carbon dioxide was also observed to increase slightly. On the other hand, the percent of methane was considerably decreased. The optimum conditions were 850 degree Celsius, corn cob content in feed of 100%, catalyst content in feed of 5% and Ni loaded on catalyst of 9%. At this condition the percentages of hydrogen and carbon monoxide were 52.0 and 18.0, respectively.     

EFFECTS OF HYBRID AND DAMAGE ON MOLD DEVELOPMENT DURING LOW TEMPERATURE DRYING AND STORAGE OF HIGH MOISTURE SHELLED CORN

Several corn hybrids either resistant or susceptible to storage mold were harvested with a combine and stored at high moistures (19 to 24% moisture, wet basis) in 0.81 m³ (23 bu) bins nd in “mini-bins” containing 1200 g (2.6 lbs). For several hybrids, two damage levels were achieved by adjusting combine cylinder speed. Storage conditions were the same as those found in a low temperature drying bin. Mold growth in the bins and “mini-bins” was monitored by determining number of propagules, percent seeds fine material was removed from all hybrids tested in 1986, whereas in 1985 it was not removed. This probably improved the storability of the 198 6 corn and reduced the differences in mold invasion. Furthermore, the sporulation and growth of mold were lower and differences may not have had time to develop.

Bin and small scale tests were consistent in differentiating the relative resistance of hybrids and they agreed with results of laboratory studies (Friday, 19,87). Some of the observed differences can be attributed to physical damage. However, there was an incremental decrease in storability above that which could be explained by damage, which the authors believe was caused by the hybrid effect. FRB73 × Mol7 was consistently more resistant to storage molds than the other hybrids tested. FRB73 × Mol7 and FR35 × FR20 displayed a higher level of mold resistance in all storage tests while P3707 and P3377 were consistently more susceptible. (Authors note: not all Pioneer hybrids are more susceptible to storage molds as some Pioneer hybrids have been found to store well in laboratory tests.)

The agreement of the bin, small scale, and laboratory studies suggests that hybrids can be screened for mold resistance in the laboratory. Hopefully, this will encourage plant breeders to begin such screening. This would be even more feasible if the laboratory procedures could be simplified and if the incubation time prior to evaluation for mold invasion could be reduced.     

蒸汽爆破膨化改性对玉米秸秆结构及复合板机械性能的影响

将玉米秸秆通过单螺杆式蒸汽爆破的方式进行膨化,得到不同类型膨化玉米秸秆,再与聚丙烯树脂（PP）复合制备复合板材。通过扫描电子显微镜（SEM）、反射红外（ATR-FTIR）、热重分析（TGA）、差式扫描量热（DSC）及鲍尔纤维筛分等测试,分析了秸秆膨化前后的纤维变化情况等。分析结果表明：SEM显示通过蒸汽爆破膨化机处理过的玉米秸秆能够有效进行"三素分离",使得玉米秸秆表面结构由规整变成纤维状和粉末碎片,并且TGA、DSC和ATR-FTIR测试结果显示：在膨化过程中纤维素结构无变化,而半纤维素和木质素发生了部分的热分解。对膨化玉米秸秆与PP复合制备的复合板材的力学性能测试发现：与未膨化玉米秸秆（CS）制备的板材相比,膨化玉米秸秆（SECS）制备的板材的冲击韧性强度和拉伸强度分别增加15.69%和17.24%,而与SECS制备的复合板材的性能相比,分别经苯乙烯-丙烯酸共聚物和乙烯-醋酸乙烯共聚物修饰的膨化玉米秸秆制备的复合板材的冲击韧性强度分别增加了156.74%和100.98%,拉伸强度分别提高了83.42%和12.03%。     

Decomposition and nutrient release from pruning residues of two indigenous agroforestry species during the wet and dry seasons

The decomposition of leaves from Cordia africana Lam. and Albizia gummifera G. F.Gmel was investigated during the wet and dry seasons at Wondo Genet (Ethiopia). Litterbags of leaves were buried in soils under farmland and shaded-coffee agroforestry systems. Residual matter was recovered after 4, 8, 12, and 16 weeks and analysed for nitrogen (N), phosphorus (P), potassium (K), cellulose, lignin, soluble polyphenol and condensed tannin content. Mass-loss and release of N, polyphenols and condensed tannins were greater from Albizia leaves than from Cordia leaves, suggesting that a high polyphenol content does not necessarily retard decomposition. The rates of mass loss and release of the majority of leaf constituents were considerably faster during the wet season than during the dry season. Lignin decomposition, however, proceeded more rapidly during the dry season, and no significant seasonal differences were observed for polyphenol decomposition. The decomposition kinetics of most leaf components during the wet season were best described by a single-exponential model, but a quadratic model provided the best fit during the dry season. Initial leaf chemistry and season were important decomposition factors, while land-use effects were negligible. However, land-use effects showed distinct seasonal differences, with leaf litter decomposing more rapidly in soil under shaded-coffee than under farmland management, especially during the wet season. This study also demonstrated that polyphenol content does not show the predictive effects it has been attributed to have and that other constituents, such as condensed tannins, would be better suited for this purpose.     

Relationship between residue quality,decomposition patterns,and soil organic matter accumulation in a tropical sandy soil after 13 years

The objectives of this study were to investigate decomposition patterns and soil organic matter (SOM) accumulation of incorporated residues (10 Mg ha⁻¹ year⁻¹) of different quality, and identify microbiological parameters sensitive to changes in SOM dynamics, in a 13-year-old field experiment on a sandy soil in Northeast Thailand. Mass loss was fastest in groundnut stover (high N), followed by rice straw (high cellulose) and tamarind (intermediate quality), and slowest in dipterocarp (high lignin and polyphenol) following a double exponential pattern. The decomposition rate k ₁ (fast pool) was positively correlated with cellulose (r = 0.70*) while k ₂ (slow pool) was negatively related to lignin (r = −0.85***) and polyphenol (r = −0.81**) contents of residues. Residue decomposition was sensitive to indigenous soil organic nitrogen (SON), particularly during later stages (R ² = 0.782**). Thirteen years’ addition of tamarind residues led to largest soil organic carbon (SOC) (8.41 Mg ha⁻¹) accumulation in topsoil (0–20 cm), while rice straw yielded only 5.54 Mg ha⁻¹ followed by the control (2.72 Mg ha⁻¹). The highest SON (0.78 Mg N ha⁻¹) was observed in the groundnut treatment. Increases in SOC were negatively correlated with cellulose content of residues (r = −0.92***) and microbial respiration (CO₂-C) losses, while SON was governed by organic N added. During later decomposition stages, there was a high efficiency of C utilization (low qCO₂) of decomposer communities especially under tamarind with the lowest qCO₂ and CO₂-C evolution loss. This study suggests that N-rich residues with low cellulose and moderate lignin and polyphenol contents are best suited to improve SOM content in tropical sandy soils.     

Root growth and phosphorus and potassium uptake by two corn genotypes in the field

In a field study P and K uptake by two corn (Zea mays L.) genotypes which differed in root growth was investigated. The effect of differences in root growth on P and K uptake was assessed using a mechanistic-mathematical model which describes nutrient uptake by growing plant roots in soil. Nitrogen was applied at 0 and 227 kg ha^–1 to Pioneer 3732 and B73xMo17 corn grown on Raub silt loam (fine-silty, mixed, mesic Aquic Argiudoll) and at 227 kg N ha^–1 to these two genotypes on Chalmers silt loam (finesilty, mixed, mesic, Typic Haplaquoll). Root growth and P and K uptake by the two corn genotypes was measured 31, 47, 75 and 91 d after planting on the Raub and 31, 47, 61 and 75 d after planting on the Chalmers soil.Root growth and P and K uptake by B73xMo17 was greater than that of Pioneer 3732 on N-fertilized Raub soil. On Chalmers soil the difference in root growth between the two genotypes resulted in an increase in K but not P uptake. The higher soil P level of the Chalmers appears to have offset possible differences in P uptake due to root size. There were no differences between the two genotypes in either the percentage of roots with root hairs, or the density or length of root hairs. Phosphorus and K uptake calculated with the simulation models for both corn genotypes on both soils over each of three growth periods agreed with observed P (Y = 0.68X + 1.71; r = 0.944^**) and K (Y = 0.88X + 15.52; r = 0.928^**) uptake. Differences in P and K uptake between B73xMo17 and Pioneer 3732 resulted primarily from the difference in root growth in the topsoil. A high correlation was found between root surface area and P (r = 0.893^**) and K (r = 0.928^**) uptake by both corn genotypes on both the soils.Journal paper No. 10,316 Purdue Univ. Agric. Exp. Stn., W. Lafayette, In 47906. Contribution from the Dep. of Agron. This paper was supported in part by a grant from the Tennessee Valley Authority.