Summary Four herbicides commonly used in Israel for controlling weeds in peanuts were evaluated under field and screenhouse conditions. Terbutryn (Terbutrex 50, w.p.), ethalfluralin (Sonalan 333, e.c.), dinitramine (Cobex 240, e.c.) and alachlor (Alapaz 480, e.c.), used at recommended levels, had no adverse effect on nodulation rate, nitrogenase activity, total nitrogen of peanut tops or pod yield, compared with control (inoculated but herbicide non‐treated) plants. Studies were conducted to determine the relative toxicity in vitro of the herbicides on each of four Rhizobium strains used for commercial peat inoculant production. The results showed that at up to 94 μg g−1 the herbicides has no inhibitory effect on the growth of rhizobia. The sensitivity of Rhizobium strains to different rates of the chemicals decreased in the order: dinitramine>alachlor>ethalfluralin>terbutryn. It was found that various strains differ in their sensitivity to the herbicides tested.

A modified procedure based Oll the cyanmethaemoglobin method for haemoglobin (Hb) determination in peanut nodules is described. It gare reliable results when tested on peanuts at all stages of vegetative growth, including when the green pigment was present in the nodules.It was shown that early (32-34 days after planting) determination of Hb in nodules of peanuts grown in a greenhouse nnder bacteriologically controlled conditions can be taken as a measure of the nitrogen-fixing ability of peanut Rhizobia and thus rauch of the time and greenhouse facilities nsually required for strain screening may be conserved.Early determination of nitrogen concentration in leaIlets of peanuts proved to be also a useful measure of Rhizobium efficiency, but less sensitive than the early determination of nodule haemoglobin.

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Seasonal fluctuations of haemoglobin (Hb) concentration in nodules and the percentage of nitrogen (N) in leaflets of rhizobium-inoculated peanuts from various planting dates, were studied under field conditions.In peanuts planted in the usual season (April, May), no correlation was found between the N and H b concentrations during the early stages of peanut growth; however, there was a very significant correlation at later periods of plant growth. W i t h July (out-of-season) planting there was no correlation between the H b and N concentrations at any time.The possibility of evaluating the atmospheric nitrogen (N2) fixation rate of peanut plants under field conditions by means of H b and N determinations was studied.