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Influence of climatic factors on clover content of white clover tall fescue rotational meadows in southern Lombardy (Italy)

P. Annicchiarico and M. Onofrii

Istituto Sperimentale per le Colture Foraggere, viale Piacenza 29. 20075 Lodi, Italy

Materials and methods
Results and discussion


One of the main disadvantages of white clover-based mixtures is their well-known, large year-to-year variation for clover content. As a consequence their feeding value, proportional to clover amount, is unreliable and can complicate formulation of balanced rations, while progressive disappearance of one of the components can lower the yields (Frame and Newbould, 1986).

Breeding can contribute to overcoming some possible causes of unbalanced clover content (Rhodes, 1991). A better definition of the physical factors capable to determine such unbalance in a given region may also prove useful by improving our capability of early prediction and consequent timely adoption of those agronomic practices, such as nitrogen fertilisation and frequency and closeness of cutting (Frame and Newbould, 1986; Harris, 1987), which can direct clover content towards a desirable value. Such value, mostly reported around 30 % on an annual dry matter (DM) basis in white clover - perennial ryegrass associations (Frame and Newbould, 1986), appears variable in relation to type of companion grass and quality targets (Giovanni, 1990; Annicchiarico and Berardo, 1993). Prediction of clover yield in pastures has already been proposed based on observation of stolon amount (Rhodes, 1991) and of number of shoot apices (Vèrtes et al., 1991).

In the present study, various climatic variables were related to variation for annual clover percent in Ladino white clover - tall fescue rotational meadows of same age and 3-year duration established at the same site in 7 different years. The contribution to prediction of annual clover content of some climatic variables in combination with other information was also preliminarily assessed.

Materials and methods

Within the framework of a large rotation trial, Ladino white clover -tall fescue rotational meadows of 3-year duration characterized by two levels of crop intensification were established each year on a sandy-loam soil in Lodi (southern Lombardy) starting from 1986. The experiment design was a randomized complete block with 3 replicates holding "meadow" and "level of intensification" as main plot and sub-plot factor, respectively. The higher level of intensification included 125 kg/ha of N, 150 kg/ha of P2O5 and 120 kg/ha of K2O per year whereas the lower level involved a 30 % reduction of these rates. The mixture comprised the white clover 'Gigante lodigiano' and the tall fescue 'Manade', which were sown around mid-March in 60 m2 plots at a rate of 3.5 and 22.5 kg/ha, respectively. The meadows were border irrigated during summer and were mowed 4 times during the first year and 5 times in each of the following years of the crop cycle. DM yield was recorded on a 15 m2 harvest area while percentage of clover, referring to green weight, was determined on a sample of about 1 kg per plot.

An analysis of variance including the factors "meadow", "level of intensification" and "year of the crop cycle" and testing the factor related to time as suggested by Littell (1989) was executed for clover content and DM yield in those 5 meadows for which information for the entire crop duration was available.

Since annual clover content in the 2- and 3- year old meadows was supposed a priori also affected by the amount of clover which occurred in the preceding year of the crop cycle, the clover percentage relatable to influence of climatic factors in each year was computed by adjusting the percentage of clover (Pij) observed in the meadow i (i = 1 to 7) at either level of intensification and at the year j (j = 1 to 3) of the cycle in function of the differences among mixtures of same age for clover content in the preceding year of the cycle. Indicating by Pi (j-1) the average annual clover percent in the meadows of age (j-1), the adjusted annual percentage of clover (APij) was computed as:

APij = Pij - (Pi (j-1) - (j-1))

The APij values for each meadow, level of intensification and year, averaged over replicates, were related to the values of various climatic variables recorded in the same year by simple correlation analysis. Data on the one-year old meadows were analysed separately from the others. The chosen climatic variables (Table 2) tried to take into account the possible occurrence of various abiotic stresses reportedly (Frame and Newbould, 1986; Harris, 1987) capable of affecting white clover and cool season grasses differently such as drought spells in periods of no irrigation, low winter temperature and late frosts, high summer temperature and, particularly until the first cut which takes place around May 10, low light intensity and sub-optimal temperature for growth.

The climatic variables about which information can be available by the end of March, together with age of the meadow (rated as 2 or 3) and clover percentage in either the penultimate or the last cut of the preceding season, were then included in a stepwise multiple regression analysis describing annual clover percent in the plots of the 2- and 3-year old meadows. Information on clover content in only one cut of the preceding year was preferred to that referring to the whole year for its lower cost. We retained as the best that model which, while maximizing the adjusted R2 value, included all variables whose partial regression coefficient was different from zero at P £ 0.01 according to t test.

Results and discussion

The higher fertilisation rate determined an overall decrease of just 3.5 % in clover content (significant at P £ 0.05) and an increase of 7.1 % in total DM yield, suggesting that response of the grass to higher N rates was partly counterbalanced by response of clover to higher P and K rates. No significant interaction between "meadow" and "level of intensification" was found. The meadows largely differed for content of clover (Table 1).

The overall differences among meadows were only partly consistent over the crop cycle, as confirmed by the significant (P £ 0.001) interaction between "meadow" and "year of the crop cycle". Had clover content been expressed on DM, the reported percent values would have been about 5 or 6 units lower given the higher quantity of water on green weight of clover compared to the grass. Clover in the first two years of the cycle fluctuated therefore around a percentage of 40 % on annual DM which seems desirable for obtainment of good feeding value in association with tall fescue (Annicchiarico and Berardo, 1993). In the third year, the amount of clover decreased on average rather steeply.

Table 1. Annual and overall clover percentage on green weight of Ladino white clover - tall fescue rotational meadows

Meadow and duration

Year of crop cycle






1986 - 88






1987 - 89






1988 - 90






1989 -91






1990 - 92






1991 - 93






1992 - 94





Average of 1st to 5tha




a means with same letters are not different at P £ 0.05 according to the Newman-Keuls test

The computation of the adjusted percent values allowed to detect rather clearly some years which were favourable for clover growth, namely 1989 and 1992, and some others which were unfavourable, namely 1987 and 1988. Range values over 7 years of the climatic variables and results of the correlation analysis are reported in Table 2.

Table 2. Range values of some climatic variables and coefficient ® of simple correlation between these variables and variation for annual clover content of Ladino white clover - tall fescue rotational meadows.

r valuesa for crop cycle year

Climatic variable

Range values


2 or 3

mean t (ºC) Sep 20 - Nov 10,

14.9 - 12.1



total rainfall (mm) Sep 1 - Oct 31

201 - 86



absolute minimum t (ºC) Jan 1 - Feb 28

-3.0 - -15.7



mean daily minimum t (ºC) Jan 1 - Feb 28

1.0 - -4.0



absolute minimum t (ºC) Mar 1 - Mar 31

1.5 - -5.0



mean t (ºC) Mar 1 - Mar 31

17.9 - 13.7



mean t (ºC) Apr 1 - May 10

13.3 - 10.4



mean heliophany (hrs) Apr 1 - May 10

6.70 - 3.68



total rainfall (mm) Apr 1 - May 31

323 - 115



mean t (ºC) Jul 1 - Aug 31

23.9 - 22.1



a * = different from zero at P £ 0.05
b of the preceding year

Variation for clover content in the first year meadows was not related to any of the given variables. In the older meadows, it was associated only to mean temperature in March. Simple linear regression of the adjusted clover content of the latter meadows on this climatic variable estimated that 1° C increase in that month would determine about 3 % increase of annual clover amount. It is noteworthy that Kleter (1968), reporting on variation of clover content in permanent meadows of The Netherlands, indicated mean temperature in April as the main climatic variable influencing that content and quantified in 1 % clover increase the effect of 1°C increase in that month. Given the higher temperature requirement for optimal growth of white clover compared to cool season grasses (Harris, 1987), low temperatures in spring can further increase the already high competitive advantage of the grass in this season.

The best model issued from stepwise multiple regression analysis is reported in Table 3.

Table 3. Adjusted R2 and mean of the absolute value of residuals at progressively increasing number of variables in the model, and estimate and significance of the partial regression coefficients (bi) of the model including all variables, following a stepwise multiple regression describing annual clover content of 2- and 3-year old Ladino white clover - tall fescue rotational meadows in function of various climatic and other variables.


adj. R2

Mean of

Estimate of bia


(mean ± SE)

Clover % at last cut of the

preceding year of crop cycle



0.55 ± 0.07***

Meadow age (2 or 3)



-17.49 ± 2.99***

Mean t (ºC) in March



2.82 ± 0.82***

a *** = different from zero at P £ 0.001 according to t test

As expected, clover percent in the last cut of the preceding year acted as a sort of starting point for the prediction since it provided the latest information on clover amount as it was before being possibly influenced by any of the given climatic variables. Also information on age of the meadow proved valuable, given the rather steep decline of clover content in the third year of the cycle. Mean temperature was the only climatic variable included in the best model. It allowed lowering of the average difference between observed and predicted clover percent of the observations used to set the model up to 7.6, a value anyway still too high for practical utilization on this kind of mixtures in the region. Further experimental data will be used for improvement and proper validation of the model.


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