Two hybrids of maize (Zea mays L.) differing in resistance to drought, were grown in chernozem soil in a greenhouse and were fertilized with two different forms of nitrogen: Ca(NO3) 2 and (NH4)2SO 4 in concentrations corresponding to 100 kg of N ha z. After emergence of the 4th leaf, plants were exposed to drought. During the drought period, the parameters of plant water status (water potential, osmotic potential, turgor pressure and relative water content) and chlorophyll a + b concentration were monitored every two days. N and K concentration and accumulation over the drought period were also monitored.Next to differences in adaptability of the two hybrids to drought, the results demonstrate different adaptability of NH 4 and NO3-treated plants within each hybrid. NH4-plants of each hybrid maintain higher turgor pressure during the drought by better osmotic adaptation. Especially significant differences appear between chlorophyll (a + b) values of NH 4 and NO3-treated plants and as affected by drought. Chlorophyll concentrations of NH4-plants are higher than those of NO3-plants both in control and droughted plants. NH 4 plants show a characteristic initial chlorophyll increase at the beginning of the drought period while in N O 3 plants chlorophyll constantly decreases throughout the whole drought period. The influence of the nitrogen form on chlorophyll concentration changes during drought does not appear to be affected by regulation of the K concentration. ~2C

No abstract

This paper outlines research on the use of lignite washery sludge as the amendment for reclamation of lignite mine soil and stimulating poplar trees growth. Sludge is characterized by high total C content ($34%) and high C/N ratio (68:1). The sludge was introduced by ploughing in, down to 20-25 cm depth, in the quantities: 0, 28, 56 and 112 t ha À1 . We have established that the N percentage in poplar leaves decreases with introducing increasing quantities of sludge into the mine soil. On the other hand, the content of B and Cd increased with increasing sludge quantities. The As content in poplar leaves did not correlate with the applied quantities of sludge, but it did with the P, Fe and Zn content in the leaves. Introducing this sludge can have a positive effect on annual tree trunk increment, but only in the subsequent phases of growth. In the first few years an increase of total C content by introducing lignite washery sludge is not sufficient to provide the conditions for faster growth of trees.

Soybean plants cv. Corsoy were grown in greenhouse conditions on sterilized quartz sand. They were inoculated with Bradyrhizobium japonicum, strain 542. The plants were treated with different concentrations of quercetin (ranging from 10 nM to 1/~M at regular intervals during the experiment. The experiment was terminated at flower development. The following parameters, important for symbiosis efficiency were determined: shoot, root and nodule weights, nodule number, total leghemoglobin in the nodules,total nitrogen and soluble protein concentrations in shoots and roots, as well as chlorophyll concentration in the leaves.The results obtained partly confirmed the earlier findings that quercetin inhibits nodulation since increasing quercetin concentration decreased the number of nodules. However, at very low concentrations, quercetin stimulated the number of nodules. Quercetin also exerted a stimulating influence on other characteristics of the plant and nodules which did not correlate with nodule number and quantity of N fixed. These are: nodule weight, leghemoglobin concentration, total soluble protein content in shoots and roots as well as shoot and root weight.

1.The ineuCnce of ammonia concentration on the distribution of nitrogen derived from opaque-2 maize uniformly-labelled with 16N has been investigated during short-term in vitro incubation of bovine rumen contents.2. Less I6N derived from maize was found in the non-protein-N (NPN) fraction during incubation without added NH, than with added NH,, due entirely to differences in the amount of N derived from maize in the NH, fraction.3. From calculations based on the transfer of N derived from maize to the NPN pool and to a bacterial fraction, it was concluded that degradation of maize protein was not influenced by NH, concentration within the examined limits. 4.The decrease in relative amount of N derived from maize in the NH, fraction at low concentrations of NH,, together with evidence for an increased fractional turnover rate of NH,-N suggests that a deficient supply of NH, is compensated for by increased catabolism of nitrogenous compounds derived from the rumen micro-organisms.Since maize grain often accounts for a large part of the diet of beef cattle, information on the pattern of degradation of maize protein in rumen contents is important in order to improve the precision with which diets are compounded. In his review Chalupa (1978) only gave a gross estimate of 40% degradability for maize.Some evidence was obtained that protein catabolism in rumen contents may be increased at low concentrations of ammonia-nitrogen In order to elucidate whether the concentration of NH,, as an end-product of protein catabolism, af€ects the rate of breakdown of dietary protein, bovine rumen contents were incubated with maize, uniformly-labelled with 15N, in the presence and absence of added NH,. The results obtained suggest that an excess of NH, does not suppress hydrolysis of maize proteins within the limits studied. EXPERIMENTAL Maize labelled with 15NMaize (hybrid ZP-SK-72-0;) grown in two successive years on a plot fertilized with 15NH4, "No, and (15NH4),S0, respectivery was used in the experiment. The ears were dried at 60° for 24 h before separation of the grain. The total and non-protein-N (NPN) contents of the two samples are shown in Table 1 along with the values for lSN content. Samples of maize used for incubation were ground to pass a 1.5 mm screen.