Soil erosion and conservation

Several mechanical methods are used to control and prevent erosion.


Flumes are artificial channels that control the flow of water down a slope and release it into an area where its impact is reduced. They are often placed at the head of gullies to prevent the backward erosion of the headwall by water flowing over the top.


Debris dams are sited in the floor of gullies. Built of wood planks or tyres, they trap material moving down the gully floor. Often this technique is used in conjunction with pair planting.

Detention dams are small dams on farms or sites such as ephemeral waterways which, under heavy rainfall, can create erosion within the waterway. The dams are designed with a wide spillway that allows some storage of water, and in flood conditions allows a steady and slow release of water over the spillway.


Where an earthflow has occurred, land smoothing is used to stabilise the soil. Bulldozers smooth the surface of the earthflow, so water will run off rather than pond and saturate the unstable soil. This technique is expensive.

Infilling can be used where tunnel gully erosion has occurred. The gully edges are pushed into the centre, which is compacted. The contour of the land is then shaped to spread run-off. This method was used successfully in the early 1960s at Wither Hills near Blenheim.


Pasture furrows were introduced in the 1950s, notably in Canterbury’s cultivated downlands, to control run-off and prevent sheet and rill erosion.

In the pasture phase of crop rotation, small channels are ploughed about 10 metres apart across the slope. These divert run-off to grassed waterways, which then feed into natural streams and rivers.

A variant of pasture furrows are graded banks, which are much wider and further apart. These were used in Northland.

Cultivation techniques

Conservation tillage is where crop-growing soils are left, after harvest, covered in crop residues. This acts as a mulch, protecting the soil from wind erosion and raindrop impact.

With contour cultivation, all cultivation is done across the slope. This creates a series of mini-barriers to the downward flow of water.

Direct drilling is a method where pasture seeds or crops are drilled straight into the soil, under pasture. The advantage is that being unploughed, the soil is not vulnerable to erosion.

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Biological Control and Natural Enemies

Biological control is the beneficial action of predators, parasites, pathogens, and competitors in controlling pests and their damage. Biocontrol provided by these living organisms (collectively called “natural enemies”) is especially important for reducing the numbers of pest insects and mites. Natural enemies also control certain rangeland and wildland weeds, such as Klamath weed (St. Johnswort). Plant pathogens, nematodes, and vertebrates also have many natural enemies, but this biological control is often harder to recognize, less-well understood, or more difficult to manage. Conservation, augmentation, and classical biological control (also called importation) are tactics for harnessing the effects of natural enemies.


Predators, parasites, and pathogens are the primary groups used in biological control of insects. Most parasites and pathogens, and many predators, are highly specialized and attack only one or several closely related pest species.


Pathogens are microorganisms including certain bacteria, fungi, nematodes, protozoa, and viruses that can infect and kill the host. Populations of some aphids, caterpillars, mites, and other invertebrates are sometimes drastically reduced by naturally occurring pathogens, usually under conditions such as prolonged high humidity or dense pest populations. In addition to naturally occurring disease outbreaks, some beneficial pathogens are commercially available as biological or microbial pesticides. These include Bacillus thuringiensis or Bt, entomopathogenic nematodes, and granulosis viruses. Additionally, some microorganism by-products such as avermectins and spinosyns are used in certain insecticides, but applying these products is not considered to be biological control.


A parasite is an organism that lives and feeds in or on a larger host. Insect parasites (more precisely called parasitoids) are smaller than their host and develop inside, or attach to the outside, of the host’s body. Often only the immature stage of the parasite feeds on the host, and it kills only one host individual during its development. However, adult females of certain parasites (such as many wasps that attack scales and whiteflies) feed on their hosts, providing an easily overlooked but important source of biological control in addition to the host mortality caused by parasitism.

Most parasitic insects are either flies (Diptera) or wasps (Hymenoptera). Parasitic Hymenoptera occur in over three dozen families. For example, Aphidiinae (a subfamily of Braconidae) attack aphids. Trichogrammatidae parasitize insect eggs. Aphelinidae, Encyrtidae, Eulophidae, and Ichneumonidae are other groups of tiny size to medium-sized wasps that parasitize pests but do not sting people. The most common parasitic flies are Tachinidae. Adult tachinids often resemble house flies. Their larvae are maggots that feed inside the host.


Insects are important food for many amphibians, birds, mammals, and reptiles. Many beetles, true bugs (Hemiptera or Heteroptera), flies, and lacewings are predators of various pest mites and insects. Most spiders feed entirely on insects. Predatory mites that prey primarily on spider mites include Amblyseius spp., Neoseiulus spp., and thewestern predatory mite (Galendromus occidentalis).

Recognizing Natural Enemies

Proper identification of pests, and distinguishing pests from their natural enemies, are essential to effectively using biological control. For example, some people may mistake aphid-eating syrphid fly larvae for caterpillars. The adult syrphid, commonly also called a flower fly or hover fly, is sometimes mistaken for a honey bee. Consult publications such as the UC Statewide Integrated Pest Management Program Pest Notes series listed in Suggested Reading to learn more about the specific pests and their natural enemies in your gardens and landscapes. Take unfamiliar organisms you find to your Cooperative Extension office or county agriculture commissioner for an expert identification. Carefully observe the creatures on your plants to help discern their activity. For example, to distinguish plant-feeding mites from predaceous mites, observe them on your plants with a good hand lens. Predaceous species appear more active than plant-feeding species. In comparison with pest mites, predaceous mites are often larger and do not occur in large groups.


Preserve naturally occurring beneficial organisms whenever possible. Most pests are attacked by several different types and species of natural enemies, and their conservation is the primary way to successfully use biological control in gardens and landscapes. Ant control, habitat manipulation, and selective pesticide use are key conservation strategies.

Pesticide Management

Broad-spectrum pesticides often kill a higher proportion of predators and parasites than of the pest species they are applied to control. In addition to immediately killing natural enemies that are present (contact toxicity), many pesticides are persistent materials that leave residues that kill natural enemies that migrate in after spraying (residual toxicity). Residues often are toxic to natural enemies long after pests are no longer affected. Even if beneficials survive an application, low levels of pesticide residues can interfere with natural enemies’ reproduction and their ability to locate and kill pests.

Biological control’s importance often becomes apparent when broad-spectrum, persistent pesticides cause secondary pest outbreaks or pest resurgence. A secondary outbreak of a different species occurs when pesticides applied against a target pest kill natural enemies of other species, causing the formerly innocuous species to become pests. An example is the dramatic increase in spider mite populations that sometimes results after applying a carbamate (e.g., carbaryl or Sevin) or organophosphate (malathion) to control caterpillars or other pests.

Eliminate or reduce the use of broad-spectrum, persistent pesticides whenever possible. Carbamates, organophosphates, and pyrethroids are especially toxic to natural enemies. When pesticides are used, apply them in a selective manner. Treat only heavily infested spots instead of entire plants. Choose insecticides that are more specific in the types of invertebrates they kill, such as Bacillus thuringiensis (Bt) that kills only caterpillars that eat treated foliage. Rely on insecticides with little or no persistence, including insecticidal soap, horticultural or narrow-range oil, and pyrethrins.

A less-persistent pesticide can result in longer control of the pest in situations where biological control is important because the softer pesticide will not keep killing natural enemies. One soft pesticide spray plus natural enemies can be effective for longer than the application of one hard spray.

Ant Control and Honeydew Producers

Ants are beneficial as consumers of weed seeds, predators of many insect pests, soil builders, and nutrient cyclers. Ants may attack people and pets or are direct pests of crops, feeding on nuts or fruit (See Pest Notes: Red Imported Fire Ants). The Argentine ant and certain other species are pests primarily because they feed on honeydew produced by Homopteran insects such as aphids, mealybugs, soft scales, and whiteflies. Ants protect honeydew producers from predators and parasites that might otherwise control them. Ants sometimes move these honeydew-producing insects from plant to plant. Where natural enemies are present, if ants are controlled, populations of many pests will gradually (over several generations of pests) be reduced as natural enemies become more abundant. Control methods include cultivating soil around ant nests, encircling trunks with ant barriers, and applying insecticide baits near plants. See Pest Notes: Ants for more information.

Habitat Manipulation

Manage gardens and landscapes by using cultural and mechanical methods that enhance natural enemy effectiveness. Grow diverse plant species and tolerate low populations of plant-feeding insects and mites so that some food is always available to retain predators and parasites. Plant a variety of sequentially flowering species to provide natural enemies with nectar, pollen, and shelter throughout the growing season. The adult stage of many insects with predaceous larvae (such as green lacewings and syrphid flies) and many adult parasites feed only on pollen and nectar. Even if pests are abundant for the predaceous and parasitic stages, many beneficials will do poorly unless flowering and nectar-producing plants are available to adult natural enemies. Reduce dust, for example, by planting ground covers and windbreaks. Dust can interfere with natural enemies and may cause outbreaks of pests such as spider mites. Avoid excess fertilization and irrigation, which can cause phloem-feeding pests such as aphids to reproduce more rapidly than natural enemies can provide control.


When resident natural enemies are insufficient, their populations can sometimes be increased (augmented) through the purchase and release of commercially available beneficial species. However, there has been relatively little research on releasing natural enemies in gardens and landscapes. Releases are unlikely to provide satisfactory pest control in most situations. Some marketed natural enemies are not effective. Praying mantids, often sold as egg cases, make fascinating pets. But mantids are cannibalistic and feed indiscriminately on pest and beneficial species. Releasing mantids does not control pests.

Only a few natural enemies can be effectively augmented in gardens and landscapes. These include entomophagous nematodes, predatory mites, and perhaps a few other species. For example, convergent lady beetles (Hippodamia convergens) purchased in bulk through mail order and released in very large numbers at intervals can temporarily control aphids; however, lady beetles purchased through retail outlets are unlikely to be sufficient in numbers and quality to provide control.

Successful augmentation generally requires advanced planning, biological expertise, careful monitoring, optimal release timing, patience, and situations where certain levels of pests and damage can be tolerated. Desperate problems where pests or damage are already abundant are not good opportunities for augmentation.


Classical biological control, also called importation, is primarily used against exotic pests that have inadvertently been introduced from elsewhere. Many organisms that are not pests in their native habitat become unusually abundant after colonizing new locations without their natural controls. Researchers go to the pest’s native habitat, study and collect the natural enemies that kill the pest there, and then ship promising natural enemies back for testing and possible release. Many insects and some weeds that were widespread pests in California are now partially or completely controlled by introduced natural enemies, except where these natural enemies are disrupted, such as by pesticide applications or honeydew-seeking ants.

Natural enemy importation by law must be done only by qualified scientists with government permits. Natural enemies are held and studied in an approved quarantine facility to prevent their escape until research confirms that the natural enemy will have minimal negative impact in the new country of release. Because classical biological control can provide long-term benefits over a large area and is funded through taxes, public support is critical for continued success. Consult Natural Enemies Handbook and Pests of Landscape Trees and Shrubs to learn about situations where imported natural enemies are important and conserve them whenever possible.

Is Biological Control “Safe”?

One of the great benefits of biological control is its relative safety for human health and the environment. Most negative impacts from exotic species have been caused by undesirable organisms contaminating imported goods, by travelers carrying in pest-infested fruit, by introduced ornamentals that escape cultivation and become weeds, and by poorly conceived importations of predatory vertebrates like mongooses. These ill-advised or illegal importations are not part of biological control. To avoid these problems, biological control researchers follow regulations and work with relatively host-specific insects.

Help preserve our environment and avoid introducing exotic new pests.

Do not bring uncertified fruit, plants, or soil into California. Take unfamiliar pests to your county agricultural commissioner or Cooperative Extension office for identification.


Although many animals prey on pest insects or mites, not all can be relied upon to reduce a pest population enough to protect plants. The most effective natural enemies are often relatively host specific, feeding on a single pest species or a group of similar pests such as aphids or scales. Good examples include predatory mites, most parasitic wasps, and syrphid flies. Very general predators such as praying mantids are often likely to kill as many beneficials as pests and thus rarely provide effective control.

Synchronization of the life cycle and environmental requirements of the pest and natural enemy also determine the effectiveness of biological control. Natural enemies that do not arrive or become abundant until after pests are very abundant may not prevent serious damage to plants. Conversely, a parasite or predator with multiple annual generations, that can attack a broad range of life stages of the pest and can feed and reproduce when pest populations are low or moderate, will likely be a more effective natural enemy.

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How to avoid Pesticide Spray Drift

Pesticide spray drift is the physical movement of spray drops from the intended target to any non-target territory and objects. Drift is not just about crop detriment; it can negatively impact farm workers, organic crops, the general public, beehives, gardens, aquatic areas and other sensitive habitats, even if the effects are not immediate or obvious.

Pesticide labels vary with regard to information on spray drift management. Some labels give a detailed list of required drift management techniques. Labels may specify a maximum wind speed in which to spray, or simply indicate not to apply under windy conditions. Labels may also require an “adequate” or specific size buffer zone between the target site and sensitive sites, such as areas occupied by humans, animals or susceptible vegetation.

The discussions continue on how prevent spray drift. A growing number of registries in certain states enable applicators to determine the location of sensitive crops in close proximity to their planned treatments. Application technology and buffer size calculations are also becoming more complicated, but ultimately it is the applicator who must take every necessary precaution.

There is no one technique that can minimize spray drift. The applicator must consider the non-target sites downwind of the application, location of buffers, weather conditions and application equipment. Follow all government regulations and label directions and carefully evaluate the following:

Non-Target Sites. Know what is downwind of your application – not only on your land, but on neighboring land as well. A small amount of spray drift to a tolerant, labeled crop on your land is very different than drift to a sensitive crop or to anything on someone else’s ownership. If possible, make the application when the wind is blowing away from any non-target site of concern.

Buffers. Establish buffers, which are areas or strips of land intended to intercept spray drift. At times, a specific buffer size will be required by the Environmental Protection Agency (EPA) when it approves the label; in other instances, the need for buffers will be assessed by the applicator based on professional judgment and local conditions. Tolerant fast-growing trees, grassed buffer strips and non-performing field borders are examples of buffers that can be positioned downwind of areas that will be treated. Know the effectiveness of the buffer as well. For example, a tall, continuous buffer of tolerant trees will provide much better protection from drift than a narrow strip of low-growing grass.

When no buffer exists (or an existing buffer is insufficient under the particular application conditions), create the needed buffer by leaving a portion of the target site untreated. The size and location of this “flexible” buffer is determined on an application-by-application basis by considering all the factors influencing spray drift potential.

Weather. Wind is the most influential weather factor affecting spray drift. Apply pesticides only when winds are light and blowing away from sensitive areas. A general rule is to spray when the wind speed is 3-10 mph, but the upper limit must be modified based on all application-specific factors influencing drift. Accurately measure wind speed and direction before and during the application.  If a change in wind speed or direction results in unacceptable drift, immediately adjust the buffer size or location as necessary, or stop the application.

Calm conditions or variable winds can actually increase the chance of spray drift. Calm conditions might indicate the presence of a temperature inversion (a trapped layer of air). Inversions, which are most common during the early morning or evening, favor horizontal movement of pesticides.

High temperatures and low relative humidity during the application may also increase the chance of spray drift by increasing evaporation, which reduces the size of spray droplets. Keep accurate records of wind speed and direction, air temperature and relative humidity.

Application Equipment. Spray pressure and volume, droplet size, nozzle type, boom height and additives can all influence spray drift. Within the constraints of the label:

  • Reduce spray pressure to produce larger spray droplets, which are less likely to drift.
  • Increase spray volume, which allows the use of nozzles that produce larger droplets.
  • Use low-drift nozzles, such as those with air-induction technology.  Replace all worn nozzles.
  • Keep the spray boom as low as possible without detrimentally affecting spray coverage. Consider boom shields and windscreens.
  • Include a drift control agent in the spray tank.

Some of these spray drift-reducing tactics cannot be used for every pesticide application because pest control will be reduced. But, if you cannot follow the label AND avoid drift, select a different product or formulation. Granules (such as weed-and-feed products) are sometimes available alternatives to the use of liquid sprays to eliminate drift.

(Source  –—Tips-To-Avoid-Pesticide-Spray-Drift.php)

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Limiting N Loss In No-till Corn And Grain Sorghum Production

         No-till production systems are being used by an increasing number of producers in the central Great Plains because of several advantages, which include:

1) reduction of soil erosion losses;

2) increased soil water-use efficiency;

3) improved soil quality.

However, the large amount of residue left on the soil can make nitrogen (N) management difficult. Nitrogen losses due to volatilization from broadcast urea-containing fertilizers in no-till production systems can be significant. Surface applications of ureacontaining fertilizers are subject to volatilization losses. Depending on conditions, losses can be 10 to 20 percent of the applied N. Nitrogen immobilization also can be a problem when N fertilizers are surface-applied in highresidue production systems. Leaching can be a further problem on coarse-textured soils when N is applied in one preplant application.

         However, on the brighter side, products that control urea solubility or affect urea hydrolysis and nitrification are available for agricultural use to help reduce volatilization, leaching, and denitrification losses. Slow solubility polymer coatings (ESN) allow urea to be released at a slower rate than uncoated urea. Recently, a new product (Nutrisphere-N) that is a copolymer of maleic and itaconic acids has become available and has shown potential in reducing urea-N losses and improving yields. Agrotain is another commercially available urease inhibitor and has proven in numerous studies to be effective in reducing N losses to volatilization. The objectives of the experiments in this discussion, one with irrigated corn and the other with dryland grain sorghum, were to 1) evaluate N efficiency from surface broadcast applications of ureacontaining N, 2) try to reduce N loss, and 3) improve efficiency with the use of products designed Limiting N Loss In No-till Corn And Grain Sorghum Production Slow-release polymer-coated urea product are beginning to become available for agricultural use.

         Summary: In both the corn and grain sorghum experiments, the treated urea products yielded better than those untreated, and were similar to ammonium nitrate. There were no significant differences in yield of ESN, Agrotain, or Nutrisphere- N. In the corn experiment that included UAN (28%), yield of UAN treated with Agrotain Plus or Nutrisphere-N was greater than that of untreated UAN. If producers wish to broadcast urea-containing fertilizer on the soil surface in no-till production systems, there are several products available that are very effective in limiting N losses and increasing N-use efficiency. to limit N volatilization and loss. Treated vs. Untreated Two studies were conducted, one with irrigated corn and the other with dryland grain sorghum. The irrigated corn study compared urea (46% N), UAN (28%), a controlled release polymer-coated urea (ESN), Agrotain, Agrotain Plus, Nutrisphere-N, and ammonium nitrate at three N rates (80, 160, and 240 lbs/A). A no-N check plot was also included. The dryland grain sorghum study consisted of untreated urea, ammonium nitrate, ESN, and urea treated with Agrotain or Nutrisphere-N. Nitrogen rates included were 40, 80, and 120 lbs/A as well as a no-N check. Both studies were conducted on Crete silt loam soils.

         Irrigated. Grain yield of irrigated corn plots receiving untreated urea was lower than plots receiving urea treated with Agrotain, ESN or Nutrisphere-N at all levels of applied N (Table 1). Yields achieved with Agrotain, ESN and Nutrisphere were equal to those of ammonium nitrate. Yields achieved with UAN (28%) alone were also lower than those from UAN treated with Agrotain, Agrotain Plus, or Nutrisphere-N. When averaged over N rates…<more>

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Reducing Methane Emissions from Irrigated Rice

Rice is grown on more than 140 million hectares worldwide and is the most heavily consumed staple food on earth. Ninety percent of the world’s rice is produced and consumed in Asia, and 90 percent of rice land is—at least temporarily—flooded. The unique semiaquatic nature of the rice plant allows it to grow productively in places no other crop could exist, but it is also the reason for its emissions of the major greenhouse gas (GHG), methane. 

Methane emissions from rice fields are determined mainly by water regime and organic inputs, but they are also influenced by soil type, weather, tillage management, residues, fertilizers, and rice cultivar. Flooding of the soil is a prerequisite for sustained emissions of methane. Recent assessments of methane emissions from irrigated rice cultivation estimate global emissions for the year 2000 at a level corresponding to 625 million metric tons (mt) of carbon dioxide equivalent (CO2e).

Midseason drainage (a common irrigation practice adopted in major rice growing regions of China and Japan) and intermittent irrigation (common in northwest India) greatly reduce methane emissions. Similarly, rice environments with an insecure supply of water, namely rainfed rice, have a lower emission potential than irrigated rice. Organic inputs stimulate methane emissions as long as fields remain flooded. Therefore, organic inputs should be applied to aerobic soil in an effort to reduce methane emission. In addition to management factors, methane emissions are also affected by soil parameters and climate.

Recent studies suggest that rice cultivation is an important anthropogenic source of not only atmospheric methane but also of N2O. Rice soils that are flooded for long periods of the year tend to accumulate soil organic carbon, even with complete removal of above-ground plant biomass. Significant input of carbon and nitrogen is derived from biological activity in the soil–floodwater system, and conditions are generally more favorable for the formation of conserved soil organic matter. It is currently unknown whether rice systems in the tropics and subtropics truly sequester atmospheric carbon and how soil organic carbon levels will react to a changing climate or new management practices.

Losses of soil organic carbon are of major concern for certain developments in the agricultural sector that are undergoing rapid intensification and diversification of crop land. At the International  Rice Research Institute (IRRI), however, 12 years of continuous rice
cropping in flooded fields did not cause any significant decline in soil  organic carbon. In contrast, the soil organic carbon immediately declined after a shift to a nonflooded system, namely maize. The modification of flooding patterns encompassing one or more dry periods may somehow accelerate decomposition, but—unlike a complete shift to upland systems—the recurring periods of flooding will keep  the overall soil organic carbon at a fairly stable level. Thus, we do not include CO2 emissions in our considerations of mitigation options.

Changing water management appears to be the most promising mitigation option and is particularly suited to reducing emissions in irrigated rice production. Midseason drainage and intermittent irrigation reduce methane emissions by over 40 percent. Shallow flooding provides additional benefits, including water conservation and increased yields. A recent study estimates large potential for additional methane reductions from Chinese rice paddies through modifications of water-management strategies, even though midseason drying is widely practiced there.

Midseason drainage or reduced water use also creates nearly saturated soil conditions, which may promote N2O production. There are conflicting reports on the net global warming potential (GWP) of midseason drainage, but there seems to be a growing consensus that this practice decreases the net GWP of paddy fields as long as nitrogen is applied in appropriate doses. According to an empirical model proposed by Yan et al. (2005), midseason drainage generally tends to be an effective option for mitigating net GWP, although 15 to 20 percent of the benefit gained by decreasing methane emission was offset by the increase in N2O emission… <more>


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