ABSTRACT


Elías Letelier Almeyda1
 
The Departamento de Investigaciones Agrícolas carried on between the year 1940-1946 a series of field trials on the effect of tue "four elements' (N P K Ca) on wheat; results of these trials are summarized in this article. Besides, results of a series of factorial field trials on the effect of "rates of aplication of lime and phosphorous fertilization" on wheat are presented by the first time.An attempt at interpreting these results is made considering the modern criteria about the function of liming.In the trials on "four elements" it was found out that lime increases yields in the acids soils, south of the Maule river; these increases are not so common as the increases induced by nitrogen or phosphorous. The effect of liming is important in granitic soils and in red clays but it is erratic and generally small in volcanic soils ("trumaos"); among the volcanic soils, that of Victoria was the one in which the response to lime was better.Trials on "rates of aplication of lime and phosphorous" were located only in soils south of the Maule; they were carried on between the years 1947-1951. Several rates of aplication of lime (500 to 4000 Kg. CaO per Ha.) were tested combined with different amounts of phosphorous fertilization (50 to 300 Kg. P2O5/Ha.).All the soils tested gave a big response to phosphorous. Same as in the "4 elements" trials, response to lime in "trumaos" was erratic and rather small, and was marked and constant in granitic soils and red clays. Response to lime in all the soils tested tend to decrease when the rate of phosphorous fertilization is increased. When the highest rate of phosphorous is used (300 Kg. P2O5/Ha.) response to lime nearly desappears.When common rates of phosphorous fertilization are used (50 Kg. P2O5/Ha.) this interaction is small and practically the effect of the combined application of P and Ca amounts to the addition of the effectsof P and Ca.The maximum yield produced by liming ammounts to 40% overthe control in Collipulli and about 25% in Cauquenes. This effect isreached when 1000 Kg. CaO (as carbonate) are applied in Collipulli;in Cauquenes it is not possible to say accurately at which rate of limingthe maximum yield is obtained. The maximum yields induced by limingare about the same as the effect produced by 50 Kg. P2O5 in Cauquenesand Collipulli.Maximum effects from phosphorous fertilization were not reachedin any of the soils in which the trials were carried on.The average increase of the yield produced using 300 Kg. P2O5/Ha. was about 60% over the control; in Collipulli the increase was morethan 100%.The observed interaction between liming and rates of phosphorousfertilization is thought to be produced by a partial movilization of thephosphorous fixed in acid conditions, induced by lime.When big amounts of available phosphorous exists in the soil thiseffect of liming is very small, according to the law of disminishingreturns.And attempt to study the relation between effect of liming,response to phosphorous fertilization, level of organic matter and pHis made.It seems probable that there are more chances of getting a responseto liming when the reserves of available phosphorous are reducedand when the pH and the leve! of organic matter are low.At the present time, the best indication of lime response in chileansoils is the soil association: response is most common in granitic soilsand red clays; response is uncertain in volcanic soils. The figures of pH,available phosphorous and level of organic matter can be used as andaid in the diagnosis of lime requirement.The rate of liming necessary to reach the maximum yields in thesoils where there is a response, has not been determined accurately inthese experirnents. Only in Collipulli this rate was determined withaccuracy: 1000 Kg. CaO/Ha. Variations in recommended rates of limeseem advisable based on the pH, the buffer capacity of the soil and,possibly, the amount of spring and summer rainfall.The reason for thisis that it was observed that the soils of Collipulli and Cauquenes changedtheir pH more slowly than it would be expected judging only by theirbuffer capacity.Although this conclutions deals with the probable effect or limingon wheat yields, it is probable that they can be extended to the effecten the clover pasture which is grown generally after cereal crops inChile.Residual effects on clover of liming applied on wheat seems tohave a big correlation with the effect obtained on wheat the previousyear.
Key words:
1Ingeniero Agrónomo. Sección Suelos. Departamento de Investigaciones Agrícolas.