Studies of plant root growth in soils treated with amendments of varying chemical and biological stability reveal that plants respond in a more complex and holistic fashion than customarily believed.  Brinton’s team at Woods End has been using root (rhizotron) chambers to observe how fertilizers such as biochar, mature and immature compost and chemical NPK affect the whole plant’s development.

A current study with tomatoes grown in a 24″ soil profile revealed that roots respond dramatically – and differently – to varying fertilizers, whether organic or chemical.  Roots were scanned after several months of development, and surface area and root length plus root biomass can be measured. In contrast to untreated, virgin soil where plant roots exhibited fairly harmonious development (but yield was low), the addition of chemical NPK or raw manure strongly influenced morphological changes – particularly with the chemicals (also boosting above-ground yield at the expense of roots). Inorganic NPK was associated with thicker roots and significantly reduced rootlets. Composting the raw dairy manure (7 months) led to harmonious – and significantly enhanced – root development.

Fertilizers have been known to change the relationship of above-ground to below-ground (root) biomass, and therefore clearly influence the entire expression and life-cycle of the plant. Composted manure prompted the greatest amount of rootlet and root-hair development – a fact that is interesting since this could clarly assist drought-resistance, and nutrient uptake. Immature, biologically active manure was somewhat too inhibitory to roots (depending on cultivar) compared to the same material composted. Earlier findings at Woods End indicate that part of this effect is due to exhaustion of soil oxygen by high rates of decomposition (e.g. from immature compost or undegraded organic matter).