Search

Voir la prépublication How reducing synthetic nitrogen in Europe affects ecosystem carbon and biodiversity: two perspectives of the same policy, hal-03763653,; International audience; Synthetic Nitrogen (N) usage in agriculture has greatly increased food supply over the past century. However, the intensive use of N fertilizer is nevertheless the source of numerous environmental issues and remains a major challenge for policymakers to understand, measure, and quantify the interactions and trade-offs between ecosystem carbon and terrestrial biodiversity loss. In this study, we investigate the impacts of a public policy scenario that aims to halve N fertilizer application across European Union (EU) agriculture on both carbon (C) sequestration and biodiversity changes. We quantify the impacts by integrating two economic models with an agricultural land surface model and a terrestrial biodiversity model (that uses data from a range of taxonomic groups, including plants, fungi, vertebrates and invertebrates). Here, we show that the two economic scenarios lead to different outcomes in terms of C sequestration potential and biodiversity. Land abandonment associated with increased fertilizer price scenario facilitates higher C sequestration in soils (+ 1014 MtC) and similar species richness levels (+ 1.9%) at the EU scale. On the other hand, the more extensive crop production scenario is associated with lower C sequestration potential in soils (− 97 MtC) and similar species richness levels (− 0.4%) because of a lower area of grazing land. Our results therefore highlight the complexity of the environmental consequences of a nitrogen reduction policy, which will depend fundamentally on how the economic models used to project consequences.; L'utilisation de l'azote synthétique (N) dans l'agriculture a permis d'accroître considérablement l'approvisionnement alimentaire au cours du siècle dernier. L'utilisation intensive d'engrais azotés est néanmoins à l'origine de nombreux problèmes environnementaux et reste un défi majeur pour les décideurs politiques pour comprendre, mesurer et quantifier les interactions et les compromis entre le carbone des écosystèmes et la perte de biodiversité terrestre. Dans cette étude, nous examinons les impacts d'un scénario de politique publique visant à réduire de moitié l'application d'engrais azotés dans l'agriculture de l'Union européenne (UE) sur la séquestration du carbone (C) et les changements de biodiversité. Nous quantifions les impacts en intégrant deux modèles économiques avec un modèle de surface des terres agricoles et un modèle de biodiversité terrestre (qui utilise les données d'une série de groupes taxonomiques, y compris les plantes, les champignons, les vertébrés et les invertébrés). Nous montrons ici que les deux scénarios économiques conduisent à des résultats différents en termes de potentiel de séquestration du carbone et de biodiversité. L'abandon des terres associé au scénario d'augmentation du prix des engrais facilite une plus grande séquestration de C dans les sols (+ 1014 MtC) et des niveaux de richesse des espèces similaires (+ 1,9 %) à l'échelle de l'UE. En revanche, le scénario de production végétale plus extensive est associé à un potentiel de séquestration de carbone plus faible dans les sols (- 97 MtC) et à des niveaux de richesse en espèces similaires (- 0,4 %) en raison d'une surface de pâturage plus faible. Nos résultats soulignent donc la complexité des conséquences environnementales d'une politique de réduction de l'azote, qui dépendra fondamentalement de la manière dont les modèles économiques utilisés pour projeter les conséquences.

Sustainable field crop management has been considered to reach the food security issue due to global warming and water scarcity. The effect of deficit irrigation and nitrogen rates on quinoa yield is a challenging issue in those areas. In this regard, the interaction effects of different N rates (0, 125, 250, and 375 kg N ha−1) and irrigation regimes [full irrigation (FI) and deficit irrigation at 0.75 FI and 0.5 FI] on quinoa yield and water and nitrogen efficiencies were evaluated with a two-year field experiment. Increasing nitrogen fertilizer application levels from 250 to 375 kg N ha−1 under FI and deficit irrigation did not cause a significant difference in seed yield and the total dry matter of quinoa. Furthermore, 20% and 34% reductions were observed for nitrogen use efficiency (NUE) and nitrogen yield efficiency with the application of 375 kg N ha−1 compared with that obtained in 250 kg N ha−1 nitrogen fertilizer, respectively. Therefore, a Nitrogen application rate of 250 kg ha−1 and applying 0.75 FI is suggested as the optimum rate to reach the highest seed water use efficiency (0.7 kg m−3) and NUE (0.28 kg m−3) to gain 4.12 Mg ha−1 quinoa seed yield. Under non–limited water resource conditions, an FI and N application rate of 375 kg ha−1 could be used for higher seed yield; however, under water-deficit regimes, an N application rate of 250 kg ha−1 could be adequate. However, questions about which environmental factors impressively restricted the quinoa growth for optimizing the potential yield need further investigation.

Most of the world's sugar is produced from a semi-perennial plant whose root system, although being one key to its success, remains poorly understood. In this study, we sought to describe how nitrogen fertilisation is likely to affect the development of the sugarcane root system and can have significant agronomic implications. We studied sugarcane root distribution, root biomass production and root N accumulation from soil cores sampled down to a depth of 1 m throughout the growth cycle of a ratoon crop in a 144 kgN ha−1 year fertilised plot and at crop harvest in six ratoon plots with fertilisation ranging from 0 to 330 kgN ha−1 year. The development of the root system in the fertilised sugarcane plot showed 1/homogeneous colonization of the topsoil by fine roots from the early phase, followed by 2/a progressive development of thicker roots mainly localised under the sugarcane row. The results suggested that nitrogen fertilisation could reduce root density in the topsoil layer. The root-to-shoot ratio of biomass and N mass decreased, respectively, from 2.1 to 0.3 and from 1.2 to 0.7 throughout an annual crop growth cycle in a fertilised plot. When sugarcane was not fertilised, an increase of 70% root biomass was observed as compared to fertilised sugarcane. In addition, approximately half of the cane N mass was found in the root compartment of the non-fertilised crop. The root system of sugarcane appeared to be a major pool of N that should be considered in studies dealing with fertiliser N use efficiency and N cycling in sugarcane agroecosystems.

Yam (Dioscorea spp.) is an important source of food for millions of people throughout the tropics. Yam yields are constrained by several factors such as low soil fertility and a poor response of the crop to nutrient supply. Here we present an experimental and modeling study performed to test the hypothesis that N leaching in the humid tropics is a key factor that explains the poor response of water yam (Dioscorea alata L.) to N fertilization. A field experiment was carried out to assess the impact of three levels of N supply (50, 125 and 200 kg N ha−1) on crop growth and soil N availability. The N fertilizer was split into two equal doses (i.e., 50%/50% split ratio), one applied just before emergence and the other a month after tuber initiation, which corresponds to the current management used by farmers. The CropSyst-Yam model was adapted to include a new soil-crop N component describing the effects of limiting N conditions on yam growth, and then to test different N fertilizer managements. The experimental results indicated that all variables linked to the soil-crop system were affected by the increase in N supply (soil N availability, crop biomass, leaf area and N uptake), and the model well described these impacts. Nitrogen leaching throughout the field experiment represented about one third of the total N supplied by each treatment. Observed and predicted data revealed that N leaching reduced yam growth under the N50 and N125 treatments by reducing soil N availability near the tuber initiation stage. This effect was not observed under the N200 treatment. Model results showed that N leaching and its negative impact near tuber initiation in N50 and N125 could be diminished by advancing the second N application by two or three weeks, and by using a split ratio of 70%/30%. Model results also indicated that this fertilizer strategy would even be suitable during very rainy growing seasons.

Sustainable alternatives to slash-and-burn shifting cultivation in the (sub)humid tropics rely on the use of external nutrient inputs to address soil fertility decline. The use of organic inputs is widely accepted as a practice to improve soil fertility, in particular soil organic carbon (SOC). On the other hand, its combined use with mineral fertilizer has the potential to maintain or increase crop productivity through positive interactive effects between both resources. Few studies have investigated these effects in the long term. Therefore, the objective of this study was to investigate whether maize productivity and soil SOC can be sustained under permanent cropping with sole and combined use of compost and mineral nitrogen (N) fertilizer. Here, we report results from a long-term experiment carried out in Gagnoa, Ivory Coast, from 1971 to 1990. The experiment followed a randomized block design comprising eight replicates of 12 treatments. The two studied factors were compost (0 or 10 t DM ha−1 yr−1) and mineral N (0, 40, 80, 120, 160 or 200 kg N ha−1 yr−1) additions. Average maize grain yields of the first cropping cycles were significantly lower without compost (5.05 ± 1.57 t ha−1) than with compost addition (6.07 ± 1.31 t ha−1). The annual yield variability as shown by the standard deviation of the mean was reduced by 20% with compost addition. Without compost, 53% of the initial SOC stock in the 0–20 cm soil layer was lost, resulting in a SOC loss rate of − 0.62 t C ha−1 yr−1 compared to 21% with compost (−0.27 t C ha−1 yr−1). Compost addition therefore reduced SOC loss with an apparent SOC storage rate of 0.35 t C ha−1 yr−1. The conversion rate of organic carbon (OC) inputs to SOC was about 12%. The Introductory Carbon Balance Model (ICBM) reproduced well SOC dynamics, especially without compost. Without mineral N and without compost, maize grain yield decreased with decreasing SOC concentration until the introduction of leguminous crops in the second cropping cycle. We conclude that combined application of compost with mineral N fertilizers was effective at maintaining maize productivity but inadequate to prevent the decline of SOC stocks, despite large additions. Leguminous crops in the rotation were key for maize productivity, but probably due to effects non-related to supplementary N supply.

SUMMARYFertilization of rubber plantations has been poorly documented despite the huge economic and ecological impact of this tropical perennial crop, especially in Southeast Asia. The main objective of this paper is to provide information on the fertilization practices of rubber smallholders in Thailand and to investigate the drivers of these practices. Data were sourced from individual interviews conducted with 414 rubber smallholders. The results showed that 99.4% of the mature rubber plantations were fertilized with either chemical or organic fertilizers, or both. The average dose of chemical fertilizers was 105/53/92 kg ha−1 of N/P/K that is consistent with the national recommendations. We estimated that almost two-thirds of the plantations had intensive or very intensive fertilization practices. Geographical location, especially the distinction between historical and new rubber-producing areas, appeared as a major factor explaining differences in fertilization practices. Several drivers commonly found in the literature did not affect the fertilization practices of the rubber farmers, highlighting some specificity of perennial crops and a context where access to fertilizer was not an issue. The high economic and environmental costs of intensive fertilization practices, while their benefit to the yield of rubber plantations continues to be debated, show the need to conduct research on sustainable fertilization practices in rubber smallholdings.

SUMMARYIndigenous crops, such as jute mallow (Corchorus olitoriusL.) have high potential for improving nutrient efficiency and income source diversification of farmers in sub-Saharan Africa. A better understanding of plant responses to nitrogen (N) is essential in shedding light on the trend towards increasing fertilizer applications for commercially grown jute mallow. The aim of this study was to determine the critical N dilution curve in order to assess the N nutrition index (NNI) in jute mallow in southern Benin. Above-ground dry matter (DM) and N concentration were determined weekly during the 2010 and 2011 growing seasons and six N treatments of 0, 30, 60, 120, 180 or 240 kg N ha−1were tested under irrigated conditions. A critical N curve (Nc= 3.35 W−0.18), where W is the DM in Mg per ha, was plotted based on the N concentration in the whole plant. The critical N concentration (Nc) represents the minimal N concentration required to achieve maximum growth. According to significant differences in DM at each sampling date, data points were divided into two groups representing either N deficient or N excess conditions. All data points in the N deficient group were under the critical N curve and most data points in the N excess group were on or above the critical N curve, therefore confirming the validity of the critical N curve determined in southern Benin. The NNI calculated as the ratio between the measured N concentration and predictedNc, ranged from 0.55 to 1.30. The equation for the critical N curve and NNI determined in this study for jute mallow could potentially be used as a parameter for N application under non-deficient water conditions in southern Benin.

In the central highlands of Madagascar, blast, a serious fungal disease of rice caused by Magnaporthe oryzae, was shown to be less severe in conservation agriculture (CA) than in conventional tillage (CT) cropping systems. To assess the effects of CA cropping systems on rice susceptibility to blast and to understand the mechanisms involved, an experiment was conducted over three growing seasons in two sites (at high and mid-altitude). Two fertilization treatments, one with mineral nitrogen (N) fertilizer, and one without, were studied in interaction with two different cropping systems (CA/CT) and two rice varieties that differ in their susceptibility to blast. The performances of the two cropping systems were assessed, and results showed that yields were no higher in the CA or were lower than in CT cropping systems. The effects of the treatments on upland rice crop growth were measured by leaf N content as an indicator of N crop status, and leaf area index (LAI) as an indicator of canopy density. In all years at both sites, leaf N content during early growth stages was higher in the CT than in the CA cropping system. The LAI was lower in the CA than in the CT cropping system at the high altitude site in all three years, and in two out of three seasons at the middle altitude site. Overall, when the level of blast was high, blast was less severe in the CA cropping system and with no N fertilizer. Leaf N content and LAI were used as intermediate explanatory variables in the statistical analyses, and one or the other or both always masked the effect of the cropping system or of N fertilization. Our results show that leaf N content during early growth stages masks the effect of the cropping system on leaf blast severity. When the LAI is strongly affected by the cropping system, it also masks the effect of the cropping system on the severity of leaf and panicle blast. Very often both variables masked the effects of the cropping system and of N fertilization. These findings should help improve disease management by modifying fertilization practices and crop nutrition in conservation agriculture cropping systems.

Accurate estimations of ammonia (NH 3) emissions due to nitrogen (N) fertilization are required to identify efficient mitigation techniques and improve agricultural practices. Process-based models such as Volt'Air can be used for this purpose because they incorporate the effects of several key factors influencing NH 3 volatilization at fine spatio-temporal resolutions. However, these models require a large number of input variables and their implementation on a large scale requires long computation times that may restrict their use by public en- vironmental agencies. In this study, we assess the capabilities of various types of meta-models to emulate the complex process-based Volt'Air for estimating NH3 emission rates from N fertilizer and manure applications. Meta-models were developed for three types of fertilizer (N solution, cattle farmyard manure, and pig slurry) for four major agricultural French regions (Bretagne, Champagne-Ardenne, Ile-de-France, and Rhône-Alpes) and at the national (France) scale. The meta-models were developed from 106,092 NH3 emissions simulated by Volt'Air in France. Their performances were evaluated by cross-validation, and the meta-models providing the best approximation of the original model were selected. The results showed that random forest and ordinary linear regression models were more accurate than generalized additive models, partial least squares regressions, and least absolute shrinkage and selection operator regressions. Better approximations of Volt'Air simulations were obtained for cattle farmyard manure (3% < relative root mean square error of prediction (RRMSEP) < 8%) than for pig slurry (17% < RRMSEP < 19%) and N solution (21% < RRMSEP < 40%). The selected meta- models included between 6 and 15 input variables related to weather conditions, soil properties and cultural practices. Because of their simplicity and their short computation time, our meta-models offer a promising alternative to process-based models for NH3 emission inventories at both regional and national scales. Our approach could be implemented to emulate other process-based models in other countries.

Urban agriculture, Life-cycle inventory,Typology,Cropping system data,Treatment frequency index,Nutrient budget; International audience; In sub-Saharan Africa, urban farmers have recently intensified the production of vegetables to cope with the increasing food demand. As a consequence, such an intensification may lead to potential risks for the environment and human health. There is therefore a need for an integrated evaluation of urban agricultural practices. Here, we studied tomato production in Benin cities. We measured performances and the environmental risks. We have monitored 12 cropping systems during 6 months and we calculated the pesticide treatment frequency index (TFI), the nutrient budgets, and the field emissions. Our results show that yields were low and variable, averaging at 9,533 kg.ha−1 and ranging from 0 to 21,163 kg.ha−1. The average TFI for pesticides was 8.9. The maximum TFI of 25 was observed for an insecticide applied weekly at 2.3 times the official rate. We observed an excess of the average nutrient budget of 120 kg N and 84 kg P. ha−1. In conclusion, our study of urban tomato production revealed poor practices and high risks for health and the environment.

Legume crops are known to have low soil N uptake early in their life cycle, which can weaken their ability to compete with other species, such as weeds or other crops in intercropping systems. However, there is limited knowledge on the main traits involved in soil N uptake during early growth and for a range of species. The objective of this research was to identify the main traits explaining the variability among legume species in soil N uptake and to study the effect of the soil mineral N supply on the legume strategy for the use of available N sources during early growth. Nine legume species were grown in rhizotrons with or without N supply. Root expansion, shoot and root biomass, nodule establishment, N2 fixation and mineral soil N uptake were measured. A large interspecific variability was observed for all traits affecting soil N uptake. Root lateral expansion and early biomass in relation to seed mass were the major traits influencing soil N uptake regardless of the level of soil N availability. Fenugreek, lentil, alfalfa, and common vetch could be considered weak competitors for soil N due to their low plant biomass and low lateral root expansion. Conversely, peanut, pea, chickpea and soybean had a greater soil N uptake. Faba bean was separated from other species having a higher nodule biomass, a higher N2 fixation and a lower seed reserve depletion. Faba bean was able to simultaneously fix N2 and take up soil N. This work has identified traits of seed mass, shoot and root biomass, root lateral expansion, N2 fixation and seed reserve depletion that allowing classification of legume species regarding their soil N uptake ability during early growth.

International audience; In response to the extensive development of upland rice on the hillsides of the Malagasy highlands, alternative cropping systems based on conservation agriculture have been recommended to halt loss of soil fertility. To assess the yield performances of these cropping systems, an experiment was set up in 2003 at Andranomanelatra (1640 m asl) in the Malagasy highlands. Grain yield, yield components, biomass accumulation and nitrogen uptake of upland rice were analyzed in the 2004-2005, 2006-2006, and 2006-2007 seasons, and root length density was measured in the 2007-2008 season. The rice crop was planted every second year following two different crops: maize intercropped with soybean (M + S, with both conventional tillage and no tillage) and maize intercropped with Brachiaria ruziziensis (M + B only with no tillage). For each cropping system, two levels of fertilization were used: no fertilizer or application of organic inputs and mineral fertilizer. The season, cropping system, and fertilization treatment had significant effects on rice grain yields. Higher yields were associated with a greater number of plants per m2, which decreased significantly over the three seasons, probably due to the highly variable beginning of the rains, and in the final season, with attacks by soil insects. The rice yield with conventional tillage was the highest and differed significantly from rice yield when maize was intercropped with Brachiaria under the no-till system, but not when the maize was intercropped with soybean with no tillage. In all three seasons, grain yields were closely linked to crop N at harvest. Differences in N uptake between treatments appeared very early in the crop cycle. Under conventional tillage, root length density at 68 days after sowing was higher between 0 and 30 cm depth than with no tillage. In these cold highlands conditions, plant establishment appeared to be more difficult with no tillage and resulted in reduced plant development and plant N uptake, particularly when rice was planted after maize intercropped with Brachiaria.

The hope of precision agriculture is that through more precise timing and usage of seed, agricultural chemicals and irrigation water that higher economic yields can occur while enhancing the economic production of field crops and protecting the environment. The analyses performed in this manuscript demonstrate proof of concept of how precision agriculture coupled with crop simulation models and geographic information systems technology can be used in the cotton production system in the Mid South to optimize yields while minimizing water and nitrogen inputs. The Hood Farm Levingston Field, located in Bolivar County, Mississippi, next to the Mississippi River, was chosen as the test sight to obtain a one hectare soil physical property grid over the entire 201 ha field. The 1997 yield was used as a comparison for the analysis. Actual cultural practices for 1997 were used as input to the model. After the 201 simulations were made using the expert system to optimize for water and nitrogen on a one hectare basis, the model predicted that an increase of 322 kg/ha could be obtained by using only an average increase of 2.6 cm of water/ha and an average decrease of 35 kg N/ha.

Metadata only record An association in an alley cropping experiment of a short-term maize variety and a tree legume (Gliricidia sepium) adapted to the Sudanese Sahel region was studied from the point of view of the nitrogen balance and plot yields. Isotopic labeling applied in the field enabled the contribution to maize nitrogen nutrition from different nitrogen sources (fertilizer, prunings, and soil) to be quantified. For equal cultivated areas, alley cropping provides a maize yield greater than that of maize grown in pure stand without nitrogen fertilizer. However this yield is only 40% of that obtained in pure stands with fertilizer nitrogen. Alley cropping gives a very favourable Land Equivalent Ratio (LER) of 0.90 and 1.58 compared with N-fertilized and non-N-fertilized plots, respectively. These LERs demonstrate the increased biological efficiency of the cultivated soil in an agroforestry system. The percentage of the total nitrogen in the maize coming from prunings (Nfdp) varies between 30 and 35% and the true coefficient of nitrogen utilization of the prunings (TCUp) varies from 15-25%. In the environment of central Senegal, the percentage of total nitrogen of G. sepium coming from N2 fixation is quite low (Ndffix = 25%), and consequently, in the maize, the nitrogen coming from N2 fixation (Ndffix) is only 8%. It is therefore necessary to improve the efficiency of nitrogen fixation of G. sepium in this zone to assure the sustainability of the agroforestry system. ---Journal/Author's Abstract

The effects of various levels of cow manure (equivalent to 0–50 kg nitrogen/ha.) or ground limestone (equivalent to 0–5 tons calcium/ha.) on the expression of resistance of cassava, Manihot esculenta Crantz to the cassava mealybug, Phenacoccus manihoti Mat. Ferr., were investigated under semi-controlled conditions in the laboratory. The study was made on two varieties of cassava, Moudouma and MM79, characterized by different levels of resistance in terms of antibiosis and tolerance. The antibiotic component was evaluated by determining the intrinsic capacity for increase rc and tolerance by quantifying morphological and physiological modifications in the growth of plants induced by 2 months infestation by 100 mealybugs. The antibiotic resistance of the two varieties was reduced by both fertilizers. However, the reduction was only significant at levels of 10 and 20 kg N/ha. and 1 and 1.51 Ca/ha. for Moudouma and MM79 respectively. In both varieties, tolerance was increased by the addition of nitrogen and not modified by the addition of lime. The integration of these results into traditional cassava crops systems has also been discussed.

Le passage de la culture itinerante traditionnelle a une agriculture plus intensive est necessaire pour repondre aux besoins qui resultent de l'augmentation de la population et de l'urbanisation. Dans les annees 1960, le Gouvernement de Cote d'Ivoire avait opte pour l'etude d'une agriculture motorisee permanente a forts intrants. Divers essais ont ete mis en place pour en etudier les conditions et l'un d'entre eux a ete poursuivi pendant 20 ans. Cet essai combine des doses variables d'azote et de compost de tiges de mais et autres residus vegetaux. Tout l'essai a recu en outre une fumure PKSCaMg abondante. Pendant la premiere saison (mars a juillet), avec des pluies relativement abondantes et regulieres, il a ete cultive du mais hybride chaque annee. Pendant la deuxieme saison (septembre a decembre), plus courte et avec des pluies plus irregulieres, on a essaye successivement differentes alternatives : une deuxieme culture de mais (1971-76), laisser le sol en jachere (1977-79) ou cultiver une legumineuse (d'abord du soja de 1980 a 1983, puis des arachides en 1984-86 et enfin du niebe). Avec des doses suffisantes d'engrais, les rendements du mais au premier cycle ont varie de 5 a 7 t/ha. Ils ont diminue pendant les 5 premieres annees, puis ils se sont stabilises et ont meme augmente quand la jachere puis des legumineuses ont ete introduites au 2° cycle. Les rendements sans azote ont ete eleves pendant les cinq premieres annees, periode pendant laquelle il n'y a presque pas de reponse a l'azote: le sol sur defriche de foret a fourni beaucoup d'azote aux cultures. Sans apport d'azote, apres 5 annees de culture les rendements diminuent fortement et l'on observe une grande variabilite entre les annees. Cependant, avec une legumineuse au 2° cycle, ils ont eu tendance a nouveau a augmenter. Le compost n'est pas indispensable, mais il permet des rendements un peu plus eleves. Sans compost, les teneurs en carbone ont diminue de 1,06% a 0,57% et en azote de 1085 ppm a 640 ppm. L'apport de fortes doses de compost permet de ralentir la diminution de la matiere organique du sol, sans l'eviter completement. Les teneurs atteignent C : 0,85% et N : 880 ppm au lieu de 0,57% et 640 ppm. Les rendements tres eleves, qui ne montrent aucune tendance a diminuer, indiquent nettement que pour la culture du mais, il n'y a pas eu de degradation de la fertilite, malgre une diminution forte des teneurs en matiere organique et en azote du sol. (Resume d'auteur)

The effect of different methods of nitrogen fertilizer application on the algal flora and biological nitrogen fixation (Acetylene-reducing activity) in a wetland rice soil was studied in pot and field experiments. Broadcast application of urea inhibited nitrogen fixation and favored the growth of green algae. In contrast, deep placement of urea supergranules (1–2 g urea granules) did not suppress the growth of N2-fixing blue-green algae and permitted acetylene-reducing activity on the soil surface to continue virtually uninhibited.