is seen that maximum yield was not obtained until all three of the
deficient nutrients were applied. Also note that the deficiency of
copper or zinc (micronutrients) caused as much problems as when
phosphorus (a macronutrient) was in short supply.
explains why in many trials (and production fields) the response to
N, P and K fertilizers is often lower than expected. There has been
a lot of emphasis on the application of these macronutrients but the
response to these nutrients will be poor if there are deficiencies
of other essential plant nutrients.
trying to achieve balanced nutrition, it should be emphasized that
we are aiming at an adequate amount of nutrients, not excessive
amounts of any nutrient. Not only is an excessive level of nutrients
a waste of money, it is a potential source of pollution and can
actually reduce yields.
concept of balanced nutrition is very simple and was in fact
developed more than 150 years ago. The idea is that a crop requires
an adequate supply of all nutrients for optimum growth. If
more than one is in short supply, growth is determined by the
nutrient which is in lowest supply. This is similar to the fact that
a chain is only as strong as its weakest link.
several nutrients are in short supply, we need to apply all of them
to get optimum production. The following experiment on pasture land
illustrates this clearly.
soil was deficient in phosphorus, zinc and copper and several
combinations of fertilizer were tried and yield is shown.