Abstract
A grazed field experiment was established in 1995 to evaluate alsike clover (Trifoliun hybridum L.), red clover (Trifolium pratense L.) and white clover (Trifolium repens L.) in clover-grass mixtures under organic farming practices. In this study the effect of seed mixture (alsike clover, red clover, white clover, white and alsike clover or grass mixture), year (1997, 1998) and grazing period (5 per grazing season) on the herbage calcium (Ca), magnesium (Mg), potassium (K) phosphorous (P) and sodium (Na) contents was assessed and the relationships between botanical proportions and herbage mineral contents were studied. Herbage Ca and Na contents varied between the seed mixtures, Ca, Mg, P and Na contents between the years and all measured minerals, except Na, between the grazing periods. The white clover mixture resulted in higher Ca and Na contents. The contents of Ca and Mg were positively related with the proportions of clovers and weeds and were higher in 1997. The contents of P and K were higher in the rainy summer of 1998. The seed mixtures resulted in similar mean K/(Ca + Mg) equivalent ratios, but the Ca/P ratio was higher for the white clover mixture. Mineral rations varied between and within grazing seasons. Under organic practices the supply of minerals in the pasture herbage varied temporally and according to the botanical contents and was unable to meet fully the requirements of dairy cows. Additional mineral feeding is recommended for organic farming systems to balance the dietary mineral contents for grazing cows.;
Highlights
IntroductionIn natural systems animal products can be seen as the result of a biogeochemical cycling of nutrients
The mean values for the K/(Ca+Mg) equivalent ratio and C/P ratio were 1.84 and 1.56, respectively. In these two-three-year-old grass-clover swards, the seed mixtures were different in respect of the proportion of clovers (P < 0.001) and grasses (P < 0.05), but not for the amount of weeds in the total herbage (Table 2)
This study showed that the K/(Ca + Mg) equivalent ratio of organic pastures was adequate most of the summer, but in early summer the risk of grass tetany must be noted and additional Mg is necessary
Summary
In natural systems animal products can be seen as the result of a biogeochemical cycling of nutrients. Minerals in organic clover-grass mixtures ing systems are complex and interact with each other. Organic farming aims to minimise the use of external inputs and attempts to make the best use of local natural resources such as soil mineralisation nutrient recycling and biological N fixation (Lampkin 1994, IFOAM 2002). The summer feeding of dairy cows should mainly be based on grazing, the most natural feeding system for bovines (CEC 1999, Weller and Cooper 2001). When circumstantial limitations on herbage mass, sward structure or herbage nutritive value decrease herbage intake and milk yield, a moderate concentrate supplement is advantageous to early-mid lactating cows (Khalili et al 2002). It should be noticed that supplementary feeding affects the dietary mineral content
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