Performance of forage maize at high latitudes : plant development, agronomy and nutritive value
Abstract: Following the development of earlier maturing hybrids the cultivation of forage maize (Zea mays L.) in Northern Europe has markedly increased in recent decades. This has raised needs for greater knowledge regarding the performance of forage maize in marginal areas, such as Sweden, under current conditions. Thus, the aim of the studies presented in this thesis was to assess the utility of different techniques for evaluating the agronomic performance and nutritive values for ruminants of maize hybrids grown at high latitudes. The development of selected maize hybrids was graded during their reproductive growth stages, and the nutritive values of both the whole plants and plant fractions were analyzed using available analytical techniques, inter alia chemical, in vitro, in situ procedures and near infrared spectroscopy (NIRS). The results showed that longer cultivation times are required by maize hybrids in order to accumulate sufficient crop heat units to reach given developmental stages at high latitudes. Thus, the plants may remain immature with high moisture contents, low agronomic and nutritive values at harvest. Dry matter (DM) yields were highest for relatively late maturing hybrids (FAO 210), but the earliest maturing hybrid (FAO 180) had the highest fractional proportion of kernels and neutral detergent fibre digestibility (NDFD) at harvest. Hence, the DM intake and performance of ruminants should be highest if fed the latter. Since the maize hybrids showed nutritional differences at a given maturity (DM concentration g/kg), the effects of maturation should be addressed in trials designed to compare their potential nutritive performance. The in vitro gas production technique showed potential utility for assessing the nutritional value of forage maize, particularly the contributions of specific morphological fractions to whole plant performance. Increasing maturity reduced the in vitro NDFD in all plant fractions, but increased the rate of rumen degradation of organic matter in the whole plants due to increases in starch concentration. This conclusion was corroborated by multivariate analysis of forage nutritive value parameters using the MILK 2006 model. The evaluation of analytical techniques revealed that most tested techniques gave biased predictions of the investigated parameters and that a new calibration set would most likely improve the validity of the NIRS predictions. Overall, the results from the studies underlying this thesis indicate that the agronomic and nutritional value of forage maize hybrids cultivated at high latitudes will depend on their DM maturity at harvest, and thus on both the site and the hybrid.
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