- Boron is one of the 13 essential elements for plant growth, and is considered a micronutrient based on the concentration required for plant growth
- principle form of uptake:
- boric acid (H3BO3)
- borate (BO33-)
- boric acid is preferred over borate
- as a condition of increased pH (increased alkalinity), boric acid converts to borate
- relatively immobile in the plant
- transported primarily in the xylem via transpiration
- boron ions primarily move through the soil via diffusion
- soil conditions related to deficiencies in boron:
- acid igneous soil
- sandy soil leached by water
- calcareous soil
- soil low in organic matter
- acid peat & muck soil
Boron Requirements in Plants
- amount required for healthy plant growth: 20 ppm, in dry soil matter
- target level for soil content IG:
- TCEC < 10 = 1 ppm Boron
- TCEC > 10 = 2 ppm Boron
- minimum concentration at which no obvious deficiencies appear: 1 ppm
- sufficient concentration: 1.5 ppm
- excess (toxic) concentration: 2 ppm for a few crop species, but this level is comfortable for most crops (see Boron Toxicity)
Boron Deficiency
- soil levels: less than 1 ppm will produce deficiency symptoms
- Plants that are sensitive to boron deficiency PNSF:
- legumes
- brassicas (broccoli, cabbage, brussel sprouts, mustards, etc)
- beets
- celery
- grapes
- fruit trees
- cotton
- sugar beet
- symptoms of boron deficiency in plants PNSF:
- abnormal development of growing points (meristematic tissue)
- apical growing points eventually become stunted and die
- flowers and fruits will abort
- for some grain & fruit crops, yield and quality are significantly reduced
- plant stems may be brittle and easily break
Boron Toxicity or Excesses
- first crops to show boron toxicity symptoms: GREEN BEANS
- Sensitive to excess boron PNSF:
- cereals
- potato
- tomato
- cucumber
- sunflower
- mustard
- semi-tolerant to excess boron:
- celery
- corn
- lima beans
- peppers
- potatoes
- pumpkin
- radish
- sweet potatoes
- tomatoes
- symptoms of boron excess PNSF:
- leaf tips and margins turn brown and die
- leaves eventually assume a scorched appearance and prematurely fall off
Amending Soil Boron Levels
- Note: it’s very easy to add too much boron, so unless you have a soil test that reports your starting boron levels, it is not recommended to add any boron
- mild excesses of boron will leach out in a few years
- boron is easy to spread evenly, since it is soluble in water
- dissolve in hot water then spray uniformly on soil
- make sure to spray the boron solution directly on the soil, since leaves cannot take it up
Soil factors that affect boron uptake by plants:
- available levels in soil
- temperature & decomposition of organic matter
- soil pH: high pH (basic/alkaline) soil decreases the plant uptake of boron
Plant factors that affect boron uptake by plant:
- hybrid or variety of plant
- stage of growth
- interactions with other elements
Sources for Boron:
- organic debris, plant residues, and microorganisms are the major sources of boron
- organic matter (humus) acts as a storage facility for anions, like borate (BO33-)
-
Boron Source Formula Composition Borax Na2B4O7·10H2O 11% B Boric acid H3BO3 17.5% B Solubor Na2B8O13·4H2O 20% B
Roles in Plant Functions:
- involved in carbohydrate reactions
- associated with pollen germination & growth, as well as improving the stability of pollen tubes
- part of RNA formation (uracil)
- used in cellular activities (division, differentiation, maturation, respiration, growth, etc)
- unique and vitally important job to do IG:
- moisture conducting tubes in plant cells must be lined with B
- “B comes first, and then come the rest of the plant nutrients”
- B & silicon work together to move moisture up the vascular tubes
