Drip emitter spacing for garden and orchard on alluvial soil

Drip emitter spacing for garden and orchard on alluvial soil is a smaller job than on red ground, because the bulb under a 4 litre dripper spreads 60 to 90 cm across on river silt and the columns from four drippers around a tree merge into one wet patch the roots can work from end to end.

Drip emitter spacing for garden and orchard on alluvial soil is therefore four columns on a bearing tree where red loam wants eight, and the question that remains is how to keep that patch from joining the river underneath.

Mango, guava and citrus along the Godavari and Krishna stand on deep silt that holds water for days and, on the low ground, sits a metre above the water table. This guide covers the merged patch, the column count by age, the hours per tree from the calculator's full-cover figures, the mound that keeps the roots out of the wet, and the monsoon stop that silt demands.

The merged patch and the water under it

Alluvial soil moves water sideways as readily as down. Four drippers set a metre apart around a tree make four bulbs that meet and join into a patch two metres across within an hour of a run, and that patch holds two or three days of the tree's water once it is full. Tree roots on silt spread wide and shallow, so the patch and the feeding roots cover the same ground, and no column stands alone.

The hazard is the drainage. The river's water table lies a metre down in the dry months and rises to the furrow in a wet August, and a tree whose patch meets it stands with its feeding roots in water. Mango and citrus lose roots within days of that, the leaves yellow from the inside of the canopy, and the gummosis and root rots that take out trees in a delta orchard follow the low ground exactly.

The garden and orchard crop page says build for the mature canopy; on silt, build for the wet August as well.

• Bulb: 60 to 90 cm across, so columns a metre apart merge into one patch.
• Count: four columns on a bearing tree does what eight do on red loam.
• Storage: two or three days; alternate-day runs through the cooler months.
• Drainage: good on the levee, poor in the low ground and the monsoon.

Drip emitter spacing for garden and orchard on alluvial soil, by age

The lateral runs along the tree row at the 3 to 5 metres the planting uses, and the columns at each tree grow with it, though more slowly than on a light soil. A sapling takes one dripper 30 cm from the stem on each side of the lateral, two columns that merge at once.

By the third year, two more at a metre out make a patch under the whole young canopy. A bearing tree takes four columns in a square a metre to a metre and a half from the trunk, and a large mango at 8 metre spacing six; that is the ceiling here, because the patch is already continuous and a seventh column adds water, not reach.

The plain online lateral with emitters from elsewhere pushed in where each column should stand is the pattern the orchard drip guide leans to for trees, and on silt it is the cheaper one, since the count stays small.

A loop of the 40 cm inline pipe around the tree works too and over-supplies the patch; it suits a grower who wants one product from the drip range for the whole farm. Either way, nothing goes in the gap between trees until the canopies meet, when the patches meet with them.

The hours, per tree

A bearing tree on a 4 by 4 metre grid is about 45 litres a day from the pump in a mild month and up to 140 in the hottest weeks.

Four columns give 16 litres an hour, so the mild day is under three hours and the hottest day nearly nine, which is why the hot months on silt are run from six columns, 24 litres an hour, in two runs of under three hours each.

The silt's storage then sets the days: outside the peak, a doubled run every second day; through the hot months, the daily split; and on the low ground, short daily runs the whole year, because a doubled run on wet-footed silt reaches the river.

Mango wants a dry spell before it flowers, and silt gives it up slowly; on this soil the valve closes two or three weeks earlier than it would on red ground, and the trowel at a hand's depth under the canopy edge, not the calendar, says when the rest has taken.

Orchard trees at full cover use 2.5 to 8 mm a day, the top of it a hot-month figure for the driest district, which on one acre is roughly 10,000 to 32,000 litres at the root, or about 11,000 to 36,000 litres from the pump once drip's losses are allowed for; the water requirement calculator gives the figure for your own acreage and treats the orchard as a closed canopy, so a young or open planting needs less.

The mound, and the monsoon stop

Trees on the low ground go in on a mound, 30 to 40 cm of silt raised at planting, with the lateral looped around its shoulder. The patch then drains down into the furrows between mounds rather than sideways into the roots, and a wet August that puts water in the furrows leaves the feeding roots a hand above it. On the levee the mound is a convenience; on the backswamp it is the difference between an orchard and a replanting.

When the rain comes weekly and the furrows stay full, the drip is off until the mound comes up moist rather than shining at a hand's depth, and the runs come back short and daily as the furrows empty. This is the reverse of the red-soil rule, where the columns are dry by the second rainless day and the pump stays in the schedule.

A blocked column hides in the patch for weeks on this soil; the blocked-line guide covers flushing, and the filter it depends on is not something we stock.

• Eight columns copied from a red-soil orchard: a patch twice the size the tree needs, and the surplus to the river.
• One long doubled run on low ground: the patch joined to the water table, yellowing from inside the canopy.
• Flat planting in the backswamp: roots in standing water every August.
• The check: a trowel a hand deep under the canopy edge the morning after a run; damp and crumbling is right, glistening is a run too long.

The figures are a starting point

The 2.5 to 8 mm a day and the bulb widths are published agronomic ranges on a full canopy, not measurements from your orchard, and a delta village holds sandy levee soil and heavy backswamp inside one boundary. Treat six columns and two runs of under three hours as the hottest-month schedule for a bearing tree on a 4 metre grid, and let the trowel correct it.

The same crop on the dry upland soil is in the red-loam orchard guide, and the same silt under banana in the alluvial banana guide.

If you want the column count and the lateral length worked for your trees' age and spacing, send us the tree spacing, the planting years, the acreage and whether the field floods and we will say how many columns each tree needs now and whether the low rows want mounds.