Yes No

YesNo

Yes No

Sand SiltGravel

No

Yes

Yes

No

Is pasture green & growing?3

Decision tree for restoring flood damaged pastures1, 2, 5

Yes No

Is pasture density OK?Is pasture cover >70%

Do you need extra pasture in late winter – early springthat can’t be met byother unflooded paddocks?

Yes

Pastures still alive

When soil driesenough direct drillwith suitableperennial pasture6

Ideally soil test when appropriate & apply accordinglyDefault applications below as fall backs only.Sandy type soils - apply N, P, K, S fertiliserSilty soils – apply N + K & S fertiliserClay loams – apply N + possibly S & KApply extra N immediately to enhance pasture recovery

When soil driesenough, undersow with Italian or hybridryegrass pasture6

Pastures dead with negligible flood sediment

Flood sediment damage

¹, ², ³,…. Supplemental notes over page

No

Is pasture covered in sand or silt?

No Yes

Is the soil smelly?4

No Yes

Is there a lot of long dead grass?

Is there debris on pasture?

Yes No

Use harrows, rake etc. to collect into heaps

Is sediment <5 cm deep?6

Is sediment 5 – 10 cm deep?7

Yes No

Is sediment 10 – 25 cm deep?8

No Yes

Slash or mulch orvery shallow roterra

Wait till sediment dries thena. spread over large area of pdkb. cultivate to mix with topsoilIs this seedbed now OK?

Yes

Is sediment deep (>25 cm)?9

Silt, sand or gravel?

Do you want to graze this area over the next 2 yrs?

Consider strategiesto increase organicmatter in gravelly soil?

Is silt still very moist?

No

Sow Italian or hyrid ryegrass orsuitable forage cereal onmedium-heavy silt or sand/soil mix?

Oversow with coated Italian orhybrid ryegrass

Wait for silt to dry then lightlybreak up surface. Drill suitable forage cereal or Italian or hybridryegrass + light harrow

Increase organic matter over time by grazing & mulching. Recultivate in following autumn or spring

Apply Nitrogen fertiliserwhen possible to enhancepasture recovery

Is sediment <5 cm deep?6

Table 1. Minimum soil temperatures* at sowingTable 1. Minimum soil temperatures* at sowing Ryegrasses 100 C & risingBrassicas 120 C “ Perennial herbs 120 C “ Maize 120 C “ MilletMillet 14140 C “Sorghum 1880 C “*Measured at 10 cm depth at 9.am for 3 consecutive days

Heap gravel into heaps for later useCultivate & sow rest of paddock withItalian or hybrid ryegrass, suitable forage cereal or brassica

Frank MickanFrank MickanPasture & Fodder ConservationPasture & Fodder ConservationSpecialist, DPI, Ellinbank CentreSpecialist, DPI, Ellinbank Centre

Soil lacks air in pores. When itdries enough, cultivate and sowPerennial, Italian or hybrid ryegrass species

Supplemental Notes

1. Structure of Sediment: Sediment deposited by flood water lacks structure and organic matter, varying in texture from light to heavy, i.e. from sand to silty loam to clay. The clays and clay loams retain water for some time and if deep, machinery will bog until the majority of the layer of soil is relatively dry. Silt to silty sand sediments dry reasonably quickly but can remain moist underneath for some time. Larger sized aggregates (sand to small pebbles), usually situated near the river banks, dry very quickly. The coarser sand-type material is dropped closest to the banks and silt and clay loamy type material is deposited further down the river and further out from the banks, also resulting in river banks being higher than the surrounding areas so often trapping excess water for long periods. Can these area be drained in some way, even if a “trap door” or “One way” outlet needs constructing?

2. Fertility of silt: Silt can come from neighbour’s topsoil or poor fertility subsoil from landslips, slopes and gullies further upstream. Regardless it will be very low in organic matter, nitrogen (N), potassium (K), phosphorous (P) and possibly sulphur (S). The pH of silty sediments are often about pH6+ and the Cation Exchange Capacity (CEC) is usually very low. Due to the highly variable nutrient status and for most efficient use of fertilisers (& seed) flood affected areas should be soil tested. Do not apply large amounts of fertiliser in one topdressing on pure silts because of limited ability to store nutrients due to low organic matter (resulting in the low CEC).

Fertilisers. Sow seed with a P and N mix such as DAP (100 kg/ha) or MAP (100 kg/ha) to supply at least 20 – 25 kg/ha P & no more than about 20 kg/ha N. Research has shown that drilling seed with fertiliser is preferable to relying on only broadcast fertiliser. Avoid placing Muriate of Potash (KCl) and urea in the seed row as these can produce a salting or osmotic effect significantly reducing seed viability. Broadcast other fertilisers as recommended by soil test before sowing or after the pasture or crop has established. N, K and S, being easily leached, are most likely to be required.

3. Damage to pasture: Pastures under water for 5-7 days in winter and 2-3 days in summer will normally recover, unless covered in sediment. If pastures aren’t showing signs of recovery after a week, consider it dead. The better quality species such as ryegrasses, clovers and cereals are first to die, then kikuyu, phalaris, paspalum, tall fescue and Strawberry Clover, then couches, buttercup, bent grass, docks and other water loving weeds.

4. Is the silt smelly?: This arises from anaerobic conditions in the silt and the smell indicates that toxins are present and highly likely to affect seed germination. It is highly recommended that smelly silts be aerated and cultivated and will recover rapidly.

5. Plan recovery: Need to understand how much feed is required, when and from what source for rest of winter, spring and summer. Prioritise the affected flooded or pugged (Puggology tool) areas into light, medium and severe to help determine what needs to be rejuvenated urgently, less so, left till autumn or not at all. Do not sow all the inundated area to annuals or even short rotation ryegrasses to avoid having to resow the same large areas next autumn, possibly creating another feed pinch then. Assess each paddock using the Decision Tree over the page. Some paddocks may need further restorative work before resowing whilst others may need more time to dry out. Be conscious of future weather Re. heavy rains or more floods or beginning to dry off rapidly with respect to what is sown when. Can you do some yourself and or rely solely on a contractor who will be in high demand?

Successful establishment. Sowing should be successful if good soil/seed contact is achieved. Drilling seed + harrow or roll is preferred over harrow or roll with no seed. Power harrow + roll or light mesh/carpet is usually very successful. Only cultivate if essential but is usually successful but grazing will be delayed depending on follow up rain amounts. Sow most pasture and crop seeds no deeper than 1 – 2 cm and forage cereals about 2.5 – 4 cm and will vary slightly according to soil moisture levels.. Competition from weeds or established pastures is essential by spraying or grazing. Fertilisers before, at and/or after sowing is also essential for persistence. Species. Most ryegrass species sown in mid-late winter will take several weeks to germinate and produce a reasonable amount of feed. Pointless to sow annuals in mid-late winter since they will go to head in September/October, unless sowing to produce silage. Short rotation (Italian and hybrid) ryegrasses will produce reasonably quick feed compared to perennial ryegrass and won’t go to head till next season. Perennial ryegrasses will not produce quite so much feed initially but, if successfully sown, will last several years. Avoid mixing annuals and perennial ryegrasses or early + later maturing varieties as the range in heading dates can complicate grazing management and fodder conservation to achieve high quality.

Herbs such as Chicory and Plantain, high quality crops, are gaining popularity where suited and best sown in early spring. Once established, their tap root will engender survival over summer and tend to be pest resistant although RLEM can damage mature plantain.

A range of brassicas and their hybrids and various proprietary mixes will supply high quality feed from late spring/early summer to autumn. Summer crops (Millets, Sorghums, etc.) can be sown when soil and moisture conditions and soil temperature suit. Do not sow grass species too late in spring in case follow up rains are so low that rooting depth will not ensure pasture survival. Do not sow brassicas and herbs too early if seed is likely to rot from future heavy rains or if sown on flats and potential for pooling of rainwater. Irrigation will ensure persistence and higher production of all species. Table 1 (opposite side) shows recommended minimum soil temperatures for sowing to ensure a good and faster germination which helps to outcompete weeds. Sowing earlier usually results in failure to germinate or reduced germination very slow growth and severe competition for light and nutrients from weeds.

Further information. Talk to your respected local seed providers and DPI staff to choose the most suitable species and cultivars for your situation and when to sow.

6. Flood sediment less than 5 cm depth: If sedimentation is less than 5 cm and grass was inundated for less than 3 – 5 days (in winter) then the grass will probably break through the silt layer. Newly sown pastures may or may not recover compared to established pastures. If greater than 50% bare ground, wait for any germinating weeds to have some leaf area before spraying out and direct drilling new pastures. If only about 20 – 30% bare consider oversowing with pasture mix but graze existing pastures short before sowing and a quick follow up regraze as new germinating plants reach ~1 - 2 leaves. These plants should not be affected and the grazing will prevent them being overshadowed by the existing pasture.

7. Flood sediment 5 – 10 cm depth: Pastures will not survive being completely covered in silt so will need to be replaced. Cultivation to intermingle the original soil and new silt is recommended at these silting depths. This is because most silts are usually relatively low in fertility, contain negligible organic matter or N and have poor structure making it prone to pugging damage. Cultivation will also alleviate any possibility of a drainage barrier occurring at the interface between the silt/old pasture. Sandy silts will dry very quickly compared to medium to heavy silts.

Consider sowing Italian or hybrid ryegrasses for quicker growth where winter – early spring feed is needed and to compete against weeds. Follow up with P, S, K fertilisers & regular N topdressing as these nutrients will be low for some time until pastures are fully restored and turning over organic matter. Consider a suitable forage cereal for fast growth and then being taken off as silage at the Flag leaf (vegetative) stage or late milk-soft dough (heading) stage. (See DPI website on Forage Cereals for further information on harvesting cereals as silage)

8. Flood sediment 10 – 25 cm depth: This much silt will vary in depth across the flooded area. If possible, spreading the silt over a larger area may result in a silting depth of 10-20 cm or even less, and can be handled as described just above (No. 7). Once the silt has dried to nearly full depth, heavy machinery can be used to plough deeply aiming to mix the sediment with the topsoil. If achieved, then cultivate and sow as normal. If the final mix is largely flood sediment, then sow Italian or hybrid ryegrasses or suitable forage cereal or other deep rooted short term crop. Sow to permanent pasture following autumn or do a summer crop followed by autumn sowing. Coarse of action may depend on how much of the sediment is clay, fine - coarse sand or small to larger gravel but as for No. 7, soil fertility, organic matter, etc, will most likely be very low in the final seed bed.

9. Flood sediment greater than 25 cm depth: The deeper area, especially if low fertility coarse sand and gravel, may be graded into heaps for later removal or use as filling, etc. Will need to wait for the full depth of sediment to be reasonably dry before trying to cultivate deeply some of the areas to mix in topsoil. May need to use light machinery for final cultivation and sowing with Italian or hybrid ryegrass + harrow or suitable forage cereal. Use appropriate species and seeding rates for specific soil types. Speak to your local agronomist/seed supplier.

Source: This decision tree has been adapted from one developed on behalf of the NZ MAF Sustainable Farming Fund and Meat and Wool Innovation using information provided by many researchers, farmers and service providers.