Quantifying interactions between compound properties and macropore flow effects on pesticide leaching

The objective of this study was to investigate the interactions between compound properties and macropore flow effects on pesticide leaching. To this end, the dual‐porosity MACRO model was used to simulate leaching of 60 hypothetical compounds with widely differing sorption and degradation characteristics using a pre‐calibrated scenario from Lanna, south‐west Sweden, representing a structured clay soil. The model predicts that, in the worst case, macropore flow increases leaching by more than four orders of magnitude for moderately to strongly sorbed compounds with relatively short half‐lives. However, it was also notable that leaching of some very mobile compounds is actually reduced by macropore flow. For pesticides leaching between 0.0001 and 10% of the applied dose (without macropore flow), the impact of pesticide properties on leaching is markedly reduced. This suggests that reductions in applied dose become a relatively more attractive and effective means of decreasing leaching from structured soils. © 2000 Society of Chemical Industry     

Prediction of nitrate leaching losses from arable land under different fertilization intensities using the SOIL-SOILN models

Abstract. The ability of the SOIL-SOILN models to predict nitrate leaching rates from arable land under different fertilizer inputs is tested. The SOIL model predicts water and temperature conditions in a layered soil profile and provides driving variables for the SOILN model which describes nitrogen inputs, transformations and losses. SOILN model predictions were compared with measurements of nitrate leaching at application rates of zero, 100 and 200 kg N per hectare (NO, N100 and N200) in a long-term field experiment in south-west Sweden. Large discrepancies between model predictions and measurements of nitrate leaching were found in some years (up to 100%) and were attributed to important soil processes which are either not included in the model (macropore How) or are difficult to model satisfactorily (partitioning between surface runoff and infiltration during snowmelt periods, crop nitrogen uptake). Nevertheless, long-term mean yearly leaching losses at the different nitrogen application rates (3, 6 and 46 kg per hectare at NO, N100 and N200, respectively) were reasonably well estimated by the model.     

Simulating the impact of irrigation management on the water and salt balance in drained marsh soils (Marismas, Spain)

Abstract. Using the simulation model MACRO, this paper investigates the likely consequences of reduced irrigation inputs on the water and salt balance and crop growth in a drained, saline clay in a Mediterranean climate (Marismas, SW Spain). The model was first successfully validated against field measurements of the soil water and chloride balance, water table depths and drain outflows in the 1989 growing season. Three-year simulations were then performed assuming two different irrigation applications (60 and 75% reductions from the 1989 amount) and two different frequencies (12 or 6 irrigations per growing season). The model predictions suggested that reduced irrigation may lead to up to a 15%) increase in the chloride content of the soil profile after 3 years. Also, despite overall reductions in water discharge, slight increases in chloride leaching via field drains ( c. 4 to 8%) were predicted. The model demonstrated that encroachment of salt into the soil profile may he exacerbated by the non-equilibrium nature of water flow and solute transport ('by-passing flow') in structured clays. With reduced water supply for irrigation, more frequent applications may give marginally better crop yields for the same quantity of irrigation but at the expense of slightly increasing salt concentration in the root zone.     

Nutrient cycling and distribution in different-aged plantations of Chinese fir in southern China

The distribution in tree biomass and understorey vegetation and annual biological and geochemical cycling of total nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were measured in young, middle-aged and mature plantations (8-, 14- and 24-years old) of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) in southern China. Although >98% of nutrients occurred in the soil, soil nutrient content decreased with plantation age. Nutrient outputs from the soil exceeded inputs in stands of all ages but the net soil nutrient loss increased significantly for N, P and Ca with plantation age. Comparison of nutrient fluxes showed that the smallest (and hence limiting for nutrient cycling) fluxes were litter decomposition in the young plantation in contrast to canopy fluxes (apart from for Mg) in the middle-aged and mature plantations. Nutrient use efficiency, release of nutrients from litter decomposition and nutrient return, particularly in litterfall, increased significantly with plantation age. These results suggest that, as stand age increases, nutrient cycling in Chinese fir plantations is increasingly dominated by biological processes and becomes less dependent on external nutrient sources in rainfall and the soil. It therefore appears that prolonging the rotation length of Chinese fir plantations by approximately 5 years could be beneficial for maintaining the soil nutrient status for successive plantings.     

Wound healing in potato tuber tissue. 1. Effects of maturity at harvest

Summary Potatoes of cvs Record (maincrop) and Red Craigs Royal (second early) were harvested at intervals from 22 August to 14 October. Half of the plots were mechanically defoliated on 22 August, by which date haulms of cv. Red Craigs Royal were largely dead. Tubers of cv. Record were immature at the first lifting date and matured thereafter, particularly after defoliation. Wound healing rates were assessed from the ability of discs of tuber tissue, cut the day after harvest, to become resistant to the loss of water vapour as suberization progressed at high relative humidity. Cv. Red Craigs Royal showed little variation in wound healing rate. Wound healing in cv. Record became more rapid with increasing maturity, particularly after defoliation when it reached a maximum by 1 October. After storage until March in the following year, the effect of maturity at lifting on wound healing rate was no longer evident.

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Zusammenfassung Zweck dieser Versuche war herauszufinden ob die Intensit?t der Wundheilung unmittelbar nach der Ernte bei unreifen Knollen beeintr?chtigt war und ob irgendwelche Effekte nach Lagerung erhalten blieben. Knollen der mittelfrühen Sorte Red Craigs Royal und der sp?ten Sorte Record wurden um 22. August bis zum 14. Oktober 1979 in Intervallen geerntet. Am 22. August wurde die H?lfte der Parzellen mechanisch abget?tet, der Rest starb auf natürliche Weise ab. Das natürliche Absterben war bei der Sorte Red Craigs Royal am 22. August und bei Record am l. Oktober fast komplett. Am Tage nach jeder Ernte wurden 11×4 mm starke Scheiben aus dem Mark entnommen, nach 10 Tagen die Entwicklung der internen Widerstandsf?higkeit gegen Wasserverlust durchgeführt. Diese Massnahme stellt ein Mass der Suberinisierung der Schnittfl?che dar (Jarvis & Duncan, 1975). Die Knollen von Red Craigs Royal waren zum ersten Erntetermin reif und zeigten danach wenig ?nderungen in der Wundverheilungsrate. Die Knollen von Record hatten unreif eine langsame Wundverheilungs-Rate, bei sp?teren Ernteterminen wurde das Wundverheilen progressiv schneller, haupts?chlich bei Knollen aus den abget?teten Parzellen, und erreichte zum l. Oktober ein Maximum (Abb. 1). Abbildung l basiert auf über 10 Tage Wundheilung summierter interner Widerstandsf?higkeit, aber die Unterschiede zwischen den Behandlungen über die Wundheilperiode hinweg waren durchweg einheitlich (Abb. 2). Nach 5–7 Monaten Lagerung bei 10°C entwickelte sich interne Resistenz schneller als nach der Ernte, und blieb bei Record schneller als bei Red Craigs Royal. Die Unterschiede zwischen den Erntezeitpunkten waren jedoch nicht mehr eindeutig (Tabelle 1). Folglich ist die langsame Wundheilung bei unreif geernteten Knollen nur ein Kurzzeiteffekt. Beim Gewicht der Scheiben w?hrend der Wundheilung ergaben sich keine betr?chtlichen ?nderungen (Tabelle 2). Dies zeigt dass sich der Wassergehalt, welcher die Wundheilrate beeinflussen kann, nicht ?nderte.

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Résumé Le but de cette étude est d'étudier l'influence du niveau de maturité des tubercules sur le taux de cicatrisation des blessures immédiatement qprès récoltés à différentes dates, entre le 22 ao?t et le serve également après conservation. Des tubercules de la variété demi-précoce Red Craigs Toyal et de la variété principale Record ont été récoltés à différentes dates, entre le 22 ao?t et le 14 octobre 1979. Sur la moitié des parcelles, un défanage mécanique a été réalisé le 22 ao?t et le reste a été maintenu jusqu'à maturité. La senescence naturelle était pratiquement atteinte au 22 ao?t pour la variété Red Craigs Royal et au ler octobre pour la variété Record. Des lamelles de 11 mm × 4 mm dans le tissu médullaire des tubercules sont réalisées un jour après prélèvement et l'évolution de la résistance interne à la perte en eau, comme mesure de la subérisation à la surface des la melles, a été observée pendant 10 jours (Jarvis & Duncan, 1979). Les tubercules de la variété Red Craigs Royal étaient m?rs à la première date de récolte, et par conséquent, peu de différence dans le taux de cicatrisation a été observé. Les tubercules de la variété Record ont un faible taux de cicatrisation lorsqu'ils sont immatures, mais aux dernières dates d'arrachage la cicatrisation s'accélère, notamment pour les tubercules des parcelles défanées, quiatteint un taux maximal de cicatrisation vers le ler octobre (fig. 1). La figure l donne le total de la résistance interne pour 10 jours de cicatrisation, mais la différence entre les traitements est demeurée nette tout au long de cette période (fig. 2). Après une conservation de 5 à 7 mois à 10°C, la résistance interne à la perte d'eau s'effectue, plus rapidement qu'après la récolte et elle demeure plus forte avec la variété Record qu'avec Red Craigs Royal, mais la différence observée entre les dates d'arrachage ne para?t plus évidente (tableau 1). Donc, la lente cicatrisation des blessures pour les tubercules non m?rs n'est qu'un effet à court terme. Aucune modification substancielle n'est apparue dans le poids des lamelles pendant la période de cicatrisation (tableau 2), ceci montre que la teneur en eau qui peut influencer le taux de cicatrisation n'a pas évolué.

     

Ammonia-oxidizing communities in agricultural soil incubated with organic waste residues

The impact of organic compounds present in different kinds of organic fertilizers, i.e., anaerobically digested household waste, composted organic household waste, swine manure, and cow manure, on microbial communities in arable soil was investigated using microcosms. Soil was amended with dried residues or organic extracts of the residues and incubated for 12 weeks at 25°C. The microbial community composition was investigated by phospholipid fatty acid (PLFA) analysis, and the community of ammonia-oxidizing bacteria (AOB) was assessed by denaturing gradient gel electrophoresis (DGGE) of 16S rDNA fragments, followed by sequencing. All dried residues increased the AOB activity, determined as potential ammonia oxidation, whereas the organic extracts from the thermophilically digested waste and the swine manure caused a decreased potential activity. However, no differences in the DGGE banding patterns were detected, and the same AOB sequences were present in all samples treated with the residue extracts. Moreover, the PLFA composition showed that none of the residue additions affected the overall microbial community structure in the soil. We conclude that the AOB community composition was not affected by the organic compounds in the fertilizers, although the activity in some cases was.     

Variation in 15N 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. Received: 15 March 1996     

Factors affecting potassium leaching in different soils

Abstract. A set of lysimeter based experiments was carried out during 2000/01 to evaluate the impact of soil type and grassland management on potassium (K) leaching. The effects of (1) four soil textures (sand, loam, loam over chalk and clay), (2) grazing and cutting (with farmyard manure application), and (3) K applied as inorganic fertilizer, dairy slurry or a mixture of both sources were tested. Total K losses in the clay soil were more than twice those in the sand soil (13 and 6 kg K ha⁻¹, respectively) because of the development of preferential flow in the clay soil. They were also greater in the cut treatment than in the grazed treatment (82 and 51 kg K ha⁻¹, respectively; P 0.01), associated with a 63% increase of K concentration in the leachates from the former (6.7 ± 0.28 and 4.1 ± 0.22 mg K L⁻¹ for cut and grazed, respectively; P 0.01) because of the K input from the farmyard manure. The source of fertilizer did not affect total K losses or the average K concentration in the leachates ( P > 0.05), but it changed the pattern of these over time.