Shoot Residues Research Articles

Fluxes of nitrogen derived from plant residues and fertiliser on a cracking clay in a semi-arid environment.

The feasibility of using legume leys to redress declining levels of soil nitrogen (N) fertility on the heavy clay Vertisols of the northern Australian grain belt depends partly on the ability of plant residues to supply N directly to subsequent cereal crops. An alternative is the use of fertiliser N in continuous cereal cropping. Two experiments were conducted (one in the field, the other under polyhouse conditions) to compare the uptake of N from either plant residues or ammonium sulfate fertiliser that had been labelled with 15N. In a field trial, 15N-labelled shoots of grain sorghum and Desmanthus virgatus and ammonium sulfate were applied to micro-plots and the flux of the added N between different soil pools and a wheat crop was followed over 219 days. Only small amounts of residue-derived N (<5%) were recovered in the mineral N of the soil at a depth of 0-10 cm, whereas over 88% of the fertiliser N was present as mineral N soon after adding the fertiliser. Soil microbial biomass-N was increased following addition of residues. Recovery of added 15N in the wheat crop was much higher from the fertiliser (35%) than from the 2 residue sources (<5%). The pot trial compared a wider range of 15N-labelled residues (shoot and root residues of Desmanthus virgatus, Lablab purpureus, and sorghum) with several rates of ammonium sulfate, applied in the presence and absence of non-labelled grain sorghum residues, over 4 cropping cycles. Dry matter production and N uptake were increased by application of fertiliser N, although the response was reduced in the presence of non-labelled sorghum residues; responses to residue N were much smaller than those to fertiliser N. In the first crop following residue application <7% of residue N was recovered, increasing to 12-23% over the 4 crops. Recovery of fertiliser N by the crops increased with the rate of application, and also depended on whether it was applied together with residues. A feature of the results, in both the field and pot experiments, was the large proportion of applied 15N that could not be accounted for in either the soil or the crops, and these losses have been attributed to denitrification.

Variation in 15 N natural abundance of soil, humic fractions and plant materials in a disturbed and an undisturbed grassland

The natural abundance of δ15N in disturbed and undisturbed pasture soils was examined. From the disturbed soil, the top 10 cm of the profile was examined and the soil split into fractions based on particle size. Plant shoot and root material contained similar low enrichments in 15N, whereas recently deposited shoot residues were highly enriched. Differences between the soil fractions in observed total N did not reflect similar 15N variation. However, the enrichment of humic material extracted from the largest soil fraction was considerably lower in 15N relative to that from the smaller fractions. The complexity of the humic material from the larger fractions was less according to the E 4 /E 6 ratio. Analysis of the profile from the undisturbed soil showed increasing 15N enrichment with depth which corresponded well with visible soil horizons and showed an inverse relationship with total soil N. This 15N enrichment was mirrored by the enrichment in humic materials down the profile and also corresponded with an increasing chemical complexity as shown by the E 4 /E 6 ratio.

Spatial Relations between Oat Residue and Ceramic Spheres when Incorporated Sequentially by Tillage

AbstractSpatial characterization of crop residues and agrichemicals incorporated by tillage is needed to interpret biomass‐related soil processes. This study presents such a characterization. We first described oat residue (Avena sativa L.) and green‐sphere distributions produced by chisel plow (CP) and moldboard plow (MP) tillage and then described red‐sphere distributions when incorporated during secondary tillage. Finally the co‐location of incorporated oat residue and colored spheres was characterized. Green and red ceramic spheres were surrogates for shoot residue and incorporated agrichemical, respectively. Characterizations were derived from weights of soil and residue and counts of spheres in soil cores (1.84 cm diam. by 30 cm long, sectioned into 15 sublengths each 2 cm long). Penetration with MP was 25 cm, CP was 15 cm, and cultivator was 17 cm. The MP incorporated 67% of residue in the 10‐ to 20‐cm depth, while more that 90% of the incorporated residue in the CP was between 1 and 11 cm deep. Secondary tillage had negligible influence on these depth distributions. Green‐sphere distributions were related more closely to tool penetration than those of oat residue because root and shoot tissue were not distinguished. Fractional porosity of the 5.32‐cm3 volumes, adjusted to account for oat residue and sphere volumes, was increased ≈12% due to these materials. Many 5.32‐cm3 volumes contained no oat residue, whereas only a few volumes had concentrations ≥4 times the mean residue concentration. Although oat residue was incorporated with primary tillage, residue and herbicide surrogates were co‐located in 35% of the volumes, many of which contained large concentrations of residue. Exclusive use of either primary tillage with the same secondary tillage produces an environment for characteristically different bioactivity in the upper 10 cm.

Separating the Effects of Sorghum (Sorghum bicolor) and Rye (Secale cereale) Root and Shoot Residues on Weed Development

Greenhouse experiments that used capillary mat subirrigation to maintain constant soil moisture and to supply fertilizer continuously were conducted to evaluate the effects of sorghum or rye residue on early growth of barnyardgrass and velvetleaf. The separate effects of root residue and of shoot residue were compared to the combined effects of root plus shoot residues and to an uncovered soil control. Residues included as nontoxic controls were leached shoot tissue and poplar excelsior. Shoot residue, leached shoot tissue, and poplar excelsior were surface-applied on an equal light transmittance basis such that mass of poplar excelsior > shoot residue > leached shoot tissue. The presence of rye root residue delayed emergence of barnyardgrass. Surface-applied residues tended to decrease barnyardgrass height, but velvetleaf stem length was greater in treatments with surface residue. Although cover crop shoot residues had little effect on weed growth after 18 d, weed growth decreased in the presence of cover crop root residues and poplar excelsior.

Nitrogen economy of annual crop and pasture legumes in southwest Australia

The proportion of legume N derived from the atmosphere by N 2 fixation (%Ndfa) was assessed at a number of field sites using δ 15N natural abundance methodology for the grain legumes lupin ( Lupinus angustifolius L.) and field pea ( Pisum sativum L.) and for subterranean clover ( Trifolium subterranean L.) in annual pastures. Concurrent assessments of N accumulated in above-ground parts at peak biomass enabled N 2 fixation inputs to be estimated for the two grain legumes. For lupin, %Ndfa averaged 82 (range 74–93), resulting in fixation of 177 kg N ha −1 (range 95–283) in shoot biomass. For field pea, %Ndfa averaged 74 (60–91), with the corresponding N 2 fixation input in shoot biomass at 144 kg N ha −1 (range 54–165). Although showing greater fixation of N 2 than field pea, lupin contained a significantly lower proportion of its total plant N in mature seed. N balance data for the two grain legumes showed that after grain removal, net fixed N input as lupin shoot residues averaged 68 kg N ha −1 and that of field pea shoot residue only 3 kg fixed N ha −1. Based on selected studies in which N in root and nodule biomass were also assessed, total potential N benefits from above and below ground residues of the two species after grain harvest were estimated to be of the order of 75 kg N ha −1 for lupin and 26 kg N ha −1 for field pea. Subterranean clover's %Ndfa averaged 72 (range 0–100) in grazed pastures. Estimates of N 2 fixation inputs as above-ground biomass in standing clover for a single spring sampling averaged 35 kg N ha −1 (0–82). A full season's N 2 fixation input in such grazed pastures is suggested to be at least twice this value. Data are compared with N 2 fixation values for these three legumes elsewhere in Australia.

Caracterização bromatológica e mineral dos resíduos de broto de bambu, visando a sua utilização como alimento animal

Nesse estudo, realizado em 1992, nos Institutos Agronômico, de Tecnologia de Alimentos e de Zootecnia, procedeu-se à caracterização bromatológica e mineral dos resíduos de broto de bambu (Dendrocalamus giganteus Munro), a fim de utilizá-los como alimento animal. Os resultados mostraram que tais resíduos, constituídos basicamente por bainhas e pedaços tenros de colmo, apresentaram elevados teores de proteína (131,4 g/kg), açúcares (115,3 g/kg), fibras (235,4 g/kg) e ácido cianídrico (213 mg/kg). Essa concentração de ácido cianídrico pode causar efeito tóxico em animais, devendo-se, portanto, eliminá-lo, adotando o mesmo procedimento utilizado para a fração comestível do broto, o qual se resume no cozimento em água fervente durante 20 minutos. Após esse tratamento, os resíduos de broto de bambu podem ser utilizados como alimento animal.

Short-term net N mineralization from plant residues and gross and net N mineralization From soil organic-matter after rewetting of a seasonally dry soil

The mineralization of N from shoot residues of two legume species and a common weed component of Western Australian pastures was measured after a simulated 'summer rainfall' in a laboratory experiment using undisturbed soil cores of a loamy sand. Water was added to the surface of the cores equivalent to a single rainfall event of 10 mm water (treatment 1); or followed 48 h later by a further application of 10 mol water (treatment 2). Net mineralization and microbial biomass N were measured over 144 h following the initial rewetting of the soil cores. Three types of 15N-labelled plant residue, namely (i) lupin leaf (Lupinus angustifolium), (ii) clover (Trifolium subterraneum) shoot, burr and petiole, and (iii) capeweed (Arctotheca calendula) shoots and leaves were placed on the soil surface as large fragments and examined to assess their mineralization and incorporation into microbial biomass. The soils dried rapidly after rewetting and net mineralization of N was very low. The proportion of N as nitrate was increased in the rewetted soils with the major changes occurring in the top 5 cm of soil. However, there was very little mineralization of the surface-applied plant residues, with more than 90% of the mineral N being derived from the native organic matter. Microbial biomass showed fluctuations in both the rewetted treatments, but no consistent increase or decrease and no significant immobilization of 15N. Gross N mineralization was measured using an isotopic dilution technique involving the injection of 15N-labelled solutions into the soil. Estimates of gross N mineralization after a single rainfall event of 10 mm water were, on average, four times greater than measures of net N mineralization. Gross N mineralization rates declined as the soil dried, with three times more mineralization occurring in the 0-5 cm depth (4.73-8.93 �g g-1 day-1), compared with the 5-10 cm depth (0.86-2.38 �g g-1 day-1). A major disadvantage with the isotopic dilution method was that injection of the solutions into soil greatly increased the soil moisture content. Gross mineralization in the injected cores is likely to have been overestimated because of N movement below the sampling zone and increased microbial activity relative to non-injected cores.

Effects of fertility on biomass, phytotoxicity, and allelochemical content of cereal rye

Studies were conducted to evaluate biomass production, tissue phytotoxicity, and allelochemical content of rye (Secale cereale L.) shoots grown in three fertility regimes (low, medium or high) in the greenhouse. Wheeler rye or a polyculture of rye and hairy vetch (Vicia villosa Roth) grown with high fertility produced the greatest biomass (78.7 and 82.7 g), with the lowest root-to-shoot ratio (0.22 and 0.43) produced in the high-fertility treatments. The polyculture treatment grown with low fertility had a greater proportion of hairy vetch (18%) than when grown with high fertility (6%). Rye shoot residue phototoxicity was affected by fertility regime. Radicle elongation of cress (Lepidium sativum L.) and barnyardgrass [Enchinochloa crus-galli (L.) Beauv. I was inhibited by rye shoot residues in a modified Parker bioassay. Rye shoot residue grown with low fertility was less inhibitory to cress radicle elongation than rye residue from the medium- or high-fertility regimes. Extracts of dried rye shoots grown with high fertility were less inhibitory than extracts from other fertility regimes. The concentrations of ether extracts of rye causing 50% inhibition (I50) of cress radicle elongation were between 125 and 276 µg/ml for greenhouse-grown and 60 and 138 µg/ml for the field-grown rye shoots. The major phytotoxic compounds in the rye shoot extracts were identified as DIBOA and BOA. The concentration of DIBOA in the greenhouse-grown rye shoots ranged between 128 and 423 µg/g while BOA concentration ranged between 2.5 and 31 µg/g. DIBOA and BOA levels were lowest in rye shoots grown with high fertility. Correlations between rye shoot biomass, DIBOA and BOA concentration, and cress barnyardgrass radicle length were significant.

Nitrogen Balance of Field Pea Crops in South Western Australia, Studied Using the 15N Natural Abundance Technique

The nitrogen economies of six contrasting field pea (Pisum sativum L.) genotypes were examined at three widely separated sites in south Western Australia, using the 15N natural abundance technique to asssess proportional dependence on fixed N, harvests at peak biomass to assess total N yields and harvests at crop maturity to examine partitioning of N between seed and non harvested crop residues. The budgets for one site (Wongan Hills) included N of nodulated roots which on average comprised 12% of total plant N at peak crop biomass and 25% of recoverable plant N after harvest of seed. At this site maximum potential (residual) benefits to a following crop (peak total plant biomass N - N uptake from soil and N taken off as harvested seed) varied between genotypes from 8 to 41 g N ha-1 (mean 26; n = 6). Data for the other two sites, based solely on N budgets of above-ground parts, provided evidence of substantial site- and genotype-specific differences in N balance in terms of shoot residues (i.e. + 7 to - 24 kg N ha-1 (mean - 5) at Avondale, + 40 to - 29 (mean + 3) at Mt Barker). The results collectively indicated a general relationship between peak biomass N of a crop and its potential or otherwise to effect a net input of residue N to the ecosystem. There were, however, considerable variations between genotypes and sites due to differences in proportional dependence on fixation (range across all sites and genotypes 60-91%) and crop harvest indices for N (corresponding range 53-90%). Correlation plots were constructed from the data for N2 fixed against crop dry matter yield and residual nitrogen benefit against nitrogen harvest index. Results are discussed in relation to values for N balance of field pea and other grain legumes obtained elsewhere by other investigators.

The effect of suppression treatments on the uptake of 15N by intercropped corn from labeled alfalfa (Medicago sativa)

In greenhouse experiments, we examined the N transferred to intercropped corn from 15N-labeled alfalfa shoot residue and intact roots in an undisturbed soil system in response to two different suppression treatments and complete killing of alfalfa. The alfalfa treatments included complete killing (glyphosate only), glyphosate injury + cutting, and cutting only, with alfalfa shoot residue returned to the soil surface in all three treatments. Corn was planted in each pot following application of the treatments. When alfalfa was suppressed by glyphosate injury + cutting, corn had recovered 12% of the alfalfa N by 8 weeks of growth, but with cutting only, N recovery by corn was reduced to 4.0%. The completekill treatment resulted in 8% recovery by corn of alfalfa N. In all treatments, most of the alfalfa-N remained in the soil organic pool. A second experiment tested a cutting only treatment with 15N-labeled alfalfa residue returned to the soil surface. The 15N-labeled alfalfa residue contributed 4.1% of N to corn during the 8-week growth cycle. Twice as much 15N was found in the active microbial biomass pool in the two treatments with live intereropped plants compared to the monoculture treatments with complete killing (non-intercropped) and the control treatment of alfalfa regrowth only. An analysis of the change in the 15N content of the undisturbed alfalfa roots from just before the suppression until 8 weeks later suggested that approximately 80% of the root 15N was lost from the plant suppressed by cutting. This corresponds to 28% of the total N released from the alfalfa. The results suggest that the degree of legume suppression was a key factor in the availability of legume N to the second crop. When the two species were intercropped, more of the N available from legume residues went to plant uptake and microbial biomass and was not stabilized as quickly in the soil organic pool. Appropriate management schemes must be designed to increase N availability to the second crop without yield reduction. These studies suggest severe suppression is necessary; if successful, more of the N can be maintained in active pools.

Carbon and Phosphorus Losses from Decomposing Crop Residues in No‐Till and Conventional Till Agroecosystems

AbstractAn increased knowledge of crop residue decomposition characteristics is a critical component for nutrient cycling studies in agroecosystems. Carbon and P losses from shoot residues of maize (Zea mays L.), wheat [Triticum estivum (L.), emend. Thell], soybean [Glycine max (L.) Merr.], and shoot and root residues of crimson clover (Trifolium incarnatum L.) were compared in no‐till and conventional till systems. Grain crop residues were generally collected from senescent plants following harvest and placed in fiberglass mesh litter bags. Soybean leaf residues, however, were sampled following preharvest abscission, while crimson clover residues were collected at spring anthesis and buried only in a conventional till system. Generally, the changes in C and P content of residues were best described by exponential and/or logarithmic functions. Losses of C and P from crop residues were consistently greater, and more rapid when residues were buried vs. left on the soil surface. Crimson clover shoots lost C and P more rapidly than root residues. Generally, greater initial losses of P than of C occurred in most residues. The lack of correlation between C and P losses is believed to be due to an inital and probably variable inorganic P content that is readily leached prior to the decomposition and mineralization losses of C. Differences in the rate and magnitude of C losses were related to seasonal effects, the initial N and P content, and/or the proportional amount of lignin in the plant residues. Tillage is clearly an important regulator or driving variable for element cycling in agroecosystems.

ALLELOPATHIC ACTIVITY OF QUACKGRASS (Agropyron repens) EXTRACTS AND RESIDUES ON ALFALFA (Medicago sativa)

Experiments were conducted to characterize the allelopathic activity of quackgrass on alfalfa. Both percent germination and seedling length of alfalfa were recorded to evaluate the toxicity of aqueous extracts from rhizomes or shoots of field-grown quackgrass harvested at three stages of growth in 1984 and 1985. The length of alfalfa seedlings was more sensitive to extracts than was percentage of germination. Aqueous solutions simulating levels of salinity, cyanide content and osmotic pressure equivalent to those found in quackgrass extracts did not affect the growth of alfalfa seedlings. Only quackgrass extracts were phytotoxic to alfalfa. Similar results with hot and cold extraction procedures demonstrated that temperature did not influence the release of water-soluble toxins. Shoot extracts were generally more toxic than were rhizome extracts. Shoot extracts were more inhibitory to alfalfa seedlings when quackgrass was harvested at the vegetative stage than at later stages. Rhizome extracts did not influence the germination of alfalfa, whereas shoot extracts of vegetative quackgrass did in 1985 but not in 1984. The tolerance of alfalfa to rhizome and shoot extracts differed among eight alfalfa varieties. Incorporation of rhizome and shoot residues into the soil caused a similar level of yield reduction, whereas peat moss residues did not influence alfalfa yield. When quackgrass residues were incorporated into soil at various times before seeding, the yields of alfalfa were progressively reduced as the period of incubation was shortened. The incorporation of peat moss did not reduce the yield of alfalfa at any periods.Key words: Allelopathy, quackgrass, alfalfa, aqueous extracts, plant residues, Agropyron repens

Partitioning of ryegrass residue sulphur between the soil microbial biomass, other soil sulphur pools and ryegrass (Lolium perenne L.)

Ryegrass shoot residues, labelled with 35S, were added to an S-deficient soil. The transfer of S to the microbial biomass, to the soil S pool extractable by NaHCO3 and to growing ryegrass when present was followed over 34 weeks. After 2 weeks 16% and 15% of the S residue was found in the biomass and in the extractable S pool, respectively. Where plants were grown, they became S-deficient (shoot S <0.2%) simultaneously with the biomass showing a marked increase in C:S ratio. This eventually reached 262 from an initial value of 59. Concurrently, the extractable S pool, which included some labile organic S, decreased to <0.2 μg g−1 soil. After 34 weeks 27% of the S residue was found in the growing plant, 7% in the biomass and 2% in the extractable S pool. Some mineralization of unlabelled soil organic S was observed during the period of greatest plant growth (8–14 weeks), but not in the absence of plants. A second phase of mineralization occurred between weeks 22 and 34, concurrent with a rise in mean temperature, which was unaffected by the presence of plants or by the size of the microbial biomass. This may have been due to “biochemical” mineralization of ester sulphate. The amount of unlabelled soil S involved in active cycling was estimated to be 11%–13% of the total soil S.

Allelopathic effect of parthenium (Parthenium hysterophorus L.) extract and residue on some agronomic crops and weeds

Allelopathic effects of entire shoot extract, plant part extracts, and shoot residue of parthenium (Parthenium hysterophorus L.) on corn (Zea mays L.), ryegrass (Lolium multiflorum Lam.), wheat (Triticum aestivum L.), velvetleaf (Abutilon theophrasti Medik.), and soybean [Glycine max (L) Merr.] growth were examined. Parthenium shoot contained water-soluble materials that were toxic to root growth of velvetleaf and wheat. At 4% (w/ v) concentration, root growth of velvetleaf and wheat were reduced by 60 and 75%, respectively. The order of increasing sensitivity to parthenium was ryegrass, corn, wheat, and velvetleaf. There was a strong correlation between extract concentration and increased toxicity to test species. The toxicity of plant part extracts was also concentration dependent. At 1 and 2% (w/v), the inflorescence and leaves caused more root inhibition than stem extract. Parthenium shoot incorporated in soil at 1% (w/w) caused significantly more root inhibition of wheat than soybean, corn, and ryegrass. At 4% (w/w), root growth of all the test species was inhibited compared to the control. Toxicity of parthenium residue to wheat diminished with increasing periods of decomposition. Residue decomposed for four weeks was less toxic than the undecomposed residue.

Allelopathic effect of lantana on some agronomic crops and weeds

The allelopathic effects of dried lantana shoot residues was examined on wheat, corn, soybean, Virginia pepperweed and velvetleaf on growth over a 30-day period. Significant differences in the growth of the test species were observed. Corn was the most sensitive and wheat was least affected by lantana residues. The other three species were intermediate in their growth response to lantana. Shoot lengths were affected in corn and velvetleaf while root length was reduced in all species except wheat. The shoot dry weights of wheat and soybean were not reduced by lantana residues. In the other three species there was a significant reduction of shoot dry weight due to lantana. The root dry weights of all the five species were reduced by lantana residue. The results demonstrated an overall rate dependent response of the plant species to lantana shoot residue concentrations.

Evidence for Allelopathy by Residues and Aqueous Extracts of Rye (Secale cereale)

Under simulated no-till conditions in the greenhouse, rye (Secale cereale L. ‘Wheeler’) residues reduced emergence of lettuce (Lactuca sativa L. ‘Ithaca’) and proso millet (Panicum miliaceum L. # PANMI) by 58 and 35%, respectively, over that obtained with a wood shaving control mulch. Rye shoot tissue inhibited lettuce germination 52% more than root tissue. Petri dish bioassays of residue in soil confirmed phytotoxicity on cress (Lepidium sativum L. ‘Curly’), lettuce, barnyardgrass (Echinochloa crus-galli L. Beauv. # ECHCG), and proso millet. Radicle elongation was a more senstive measure of phytotoxicity than germination per se. Phytotoxicity increased as the distance from seeds to rye residues decreased. While rye shoot residues caused 40% greater inhibition of cress radicle elongation in sterile soil than nonsterile soil, barnyardgrass was equally inhibited in both soil regimes. Phytotoxicity decreased in nonsterile soil, indicating that the compounds were degraded by microorganisms. Phytotoxic compounds in shoots were water extractable. Cress and barnyardgrass responded similarly to both aqueous rye extracts and to residues added to soil.

Allelopathic Effects of Sporobolus pyramidatus on Vegetational Patterning

Field observations of stands of Sporobolus pyramidatus indicated a reduction of growth of S. pyramidatus in the center of the stands. Associated species were either reduced in growth or eliminated from these stands. Rapid encroachment of S. pyramidatus on Cynodon dactylon was also observed. Experiments were designed to determine if the observed vegetational patterning was a result of allelopathy. Early studies eliminated shading and soil factors as causal agents. Experiments with field soil taken from around S. pyramidatus plants indicated that phytotoxins were present and were relatively stable in the soil. Decaying shoot material exerted the most phytotoxic effect on growth and germination of the test species; however, C. dactylon was adversely affected by all factors tested except leaf leachate. Buchloe dactyloides was inhibited by field soils and, by decaying shoots. The decaying shoots of S. pyramidatus inhibited the growth of its own seedlings. There was also an indication that the leaf leachate and root exudate of S. pyrami- datus may be responsible for its own decline. Para-coumaric acid and ferulic acid were extracted from S. pyrami- datus shoot residue in large quantities. Both compounds were very inhib- itory to germination of Amaranthus palmeri seed. The results of this study show that invasion and rapid encroachment of S. pyramidatus on C. dactylon and possibly on B. dactyloides are pri- marily due to an allelopathic effect, with competitive mechanisms and mechanical disturbance probably accentuating this effect. S. pyramidatus is more inhibitory to C. dactylon than to itself, thus allowing it to invade new areas before it eliminates itself.