Grassland Research Institute
Cucului str. 5, 2200 Brasov, Romania
Materials and methods
Results and discussion
It is known that on acid soils the nutrition of plants becomes more difficult because of lack of balance in nutritients and possible toxicity problems. Many researchers have reported that the liming of acid grassland soils with values of pH 5.4-5.5 with nil mobile Al content, improves plant growth both quantitatively and qualitatively. Increases are due to the uptake by the forages of macroelements (N, P, Ca, Mg) and trace elements (Mn, Cu, Zn) close to the contents optimal for animal nutrition (Alien, 1981; Daniliuc, et. al., 1987,1988; Razec, 1989,1993).
It has also been established that the mobile Al present in acid soils has negative implications in nutrition, especially for perennial legumes (Elliot, 1979; Razec, 1989). The nutrition of plants is disturbed even in conditions when the nutrient elements are in optimal quantities for plant growth. The main objective of this paper is to examine the influence of pH and Al levels in soil on the mineral nutrition of white clover.
Research was carried out during three years in a greenhouse, in Mitscherlich pots with 8 Kg capacity, on a brown podzolic strongly acid soils, pH (H2O) - 4.53 and 102 ppm mobile A1 content, clayey-sandy texture, 3.2% humus poor in mobile P (PA12 ppm) and K(KA142 ppm).
Five pH (H2O) levels and five levels of mobile Al content in soil were studied: l) pH - 4.53, Al 102 ppm (unlimed soil); 2) pH (H2O) - 5.17, Al-30 ppm; 3) pH (H2O) - 5.33, Al - 15 ppm; 4) pH (H2O) - 5.42, Al 7 ppm; 5) pH (H2O) - 6.62, Al 0 (inaccessible). The pH levels and the mobile Al contents were achieved through liming with various CaO rates. The amendments were applied as CaO one year before sowing, in order that the soil could interact and to achieve the required pH and Al levels. Unifors N, P and K fertilizer were applied.
Measurements were made of DM yield, both vegetative material and roots, and macro and trace element contents in plants.
The decreased pH in the soil (pHH2O) - 4.53) and the increase of mobile Al content (102 ppm Al) had negative effects on growth and development of white clover plants from the start; the effects were more intense in the first and the second years but reduced in the third year.
The improvement of acidity and the decrease in mobile Al content through liming resulted in a great increase in DM yield from the 1.2-10.0 g pot-1 in the first year, 1.5-11.4 g pot-1 in the second year, until 11.5-13.8 g pot-1 in the third year. The same phenomenon was also observed in the roots. After three years of investigation, the root DM weight increased from the 3.2 g pot-1 at pH (H2O) - 4.53 up to 13.3 g pot-1 at pH (H2O) - 6.62.
The increased yield can be explained both through the removal of harmful effects from mobile Al present in soil at certain pH values and also through the changing competitive effects of the ions of Al, Ca, Mg, Na, K, etc. in taking different positions on roots in the plant's, nutrition process (Guerrier, 1979; Daniliuc, 1986).
In the aerial part of the plants (forage), increased soil pH value was accompanied by an increase of N, P, Ca, Mg contents, from poor values (P, Mg) for plant nutrition (and animal nutrition) up to values close to those optimal (Figure 1).
Decreasing soil acidity is a major factor P availability. The K element has a different behaviour compared with the other elements. Its low content on unlimed soil increases through liming up to optimal values at pH 5.4-5.5 and then decreases again at pH 6.6. This diminuation can be explained by the selective absorption of the bivalent cations (Ca, Mg).
These relations achieved between soil pH and content of macroelements of the entire plant are somewhat diminished by dilution of the contents in the vegetative part, that increases with increasing soil pH.
The correction of the acid reaction of the soil by liming and inactivation of mobile Al, existing in the unlimed soil in a potentially toxic amount, does not assure the achievement of optimum contents of P,K and Mg; for this fertilization with P and K is also necessary.
Trace element contents
There was a negative correlation between the trace element contents of the entire plant (with the exception of Cu) and the soil pH (Figure 2). At pH (H2O) - 4.53 (unlimed soil) Zn, Mn, Fe and Al contents were high indeed at toxic levels for animal nutrition, but at pH 6, they were reduced and reached optimal values.
The trace element contents of the roots have the same variation as the vegetative part but with the difference that in the roots, the content was about 5-10 times higher than those in the aerial vegetation.
Acid soils with a high content of mobile Al require liming to amend the soil pH and thus inactivating the Al.
The improvement of soil pH by liming assures not only a quantitative improvement in forage yield but also in chemical composition with values close to the optimal required for animal nutrition, i.e. the N, P, Ca, Mg, Fe, Mn, Cu, Zn contents. Between soil pH values of 4.53 to 5.33 toxic contents of Fe, Mn, Al may be present in the aerial parts of the forage. White clover is a rich source of some microelements.
ALLEN G.V. (1981) Aluminum is linked to grass tetany. Better Crops. 65, 6-10.
DANILIUC D., CARDASOL V., and POPOVICI D. (1987). Aluminum in acid soils and grassland vegetation and its impact on plant nutrition and fodder harvest, Lucrari Stiintifice I.C.P.C.P. Brasov XII, 19-33.
DANILIUC D., POPOVICI D., CIUBOTARIU C.,(1988). Influence of long-term nitrogen fertilization on chemical properties of soil and vegetation. Lucrari Stiintifice I.C.P.C.P. Brasov. XIII, 123-129.
ELLIOT R.C. (1979) Sensitivity of several species of grasses and legumes to soil acidity. Canadian Journal of Plant Science. 53: 113, 117.
RAZEC M. (1989) Relationships between the soil reaction, yield and plant chemical composition in potted perennial legumes. Lucrari Stiintifice I.C.P.C.P. Brasov. XIV, 194-204.
RAZEC M. (1993) Correlations between the reaction of the soil and production and chemical composition of the forage in some perennial grasses. Lucrari Stiintifice I.C.P.C.P. Brasov. XVI, 241-256.
Figure 1. Correlation between soil pH and content of major elements
Figure 2. Correlation between soil pH and content of trace elements