Soil texture crucial along with fertility and acidity analysis
Published 09/11/2010 | 05:00
The recent heavy showers have made field visits challenging -- and what a contrast to a couple of weeks ago. The current wet conditions have increased slug activity in the rougher seedbeds, particularly after rape crops. Weed control will have to wait until ground conditions improve and will require a good combination of contact and residual activity.
Walking some fields -- drilled with winter wheat -- in north Kildare and south Meath provided a stark contrast in soil conditions. The main reason for the difference was the soil texture and how both soils dealt with the rainfall. Farmers have always soil sampled for lime requirements and fertility levels, but few have a soil texture analysis result for their farm.
Soil texture, which is the percentage of sand, silt, clay (mineral elements) and organic matter in a soil, is fundamental to fertility, structure, and drainage characteristics. Soil fertility can be influenced by fertiliser and lime application, rotation and good tillage practice, but soil texture -- in reality -- cannot be changed, with the exception of organic matter. The classification of a soil as a clay loam, a medium loam, a sandy loam, etc, is based on the various proportions of sand, silt and clay.
Soils with a high percentage of clay are potentially more fertile relative to sandy/silt soils, hold more water, drain slowly and compact easily.
Clay soils have the ability to hold more fertiliser due to a complex reaction where inorganic fertiliser -- phosphorous and potash -- lock or bind onto the clay particles, similar to the reaction of iron filings to a magnet.
The N, P and K in fertiliser has a negative or positive charge. The clay particle also has a charge (negative), facilitating the nutrient lock-on. P and K lock on, whereas N does not very well and remains in the soil water and can be washed out.
A soil with a lot of sand will drain well, but will have low fertility as fertiliser will not lock-on due to reduced soil- to-nutrient attraction. Soils with high silt levels have low fertility potential, a tendency to compact and have poor drainage characteristics.