The effects of nitrogen fertilizer and seed inoculation on yield and quality of green beans (Phaseolus vulgaris L.)

Abstract

In the 1978 - 79 season, two field experiments were conducted to measure the effects of various times and rates of N fertilizer applications and two strains of Rhizobium bean inoculum on yield and quality of the standard commercial green bean, Gallatin 50. The first experiment compared three seed inoculation treatments (no inoculum, NZP 5232 strain and CIAT 161 strain) in factorial combination with four levels of nitrogen fertilizer (0, 20, 40, 80 kg/ha), applied at sowing while in the second experiment the same four rates of nitrogen were compared at three different times of application (at sowing; side dressing before flowering; split application of half at sowing and half before flowering).

Two pot experiments were also conducted in the winter of 1979 to supplement field data and were aimed at clarifying a) the interaction between nitrogen fertilizer and Rhizobium at two stages of growth b) the effects of nitrogen fertilizer at three stages of growth.

In Experiment I, there was no significant response to either nitrogen fertilizer or inoculation on green bean yield which was uniformly high and averaged 21.5 tonnes per hectare. This lack of response was attributed to high soil mineral N levels. In Experiment II, unfertilized beans yielded 15.85 tonnes per hectare and those fertilized with N produced an extra 1.3 tonnes but this increase was not significant. Because of the lack of response to N little could be deduced from the time of application.

In the glasshouse pot experiments on a less fertile soil, however, a significant N response in green bean yield occurred, increasing up to 40 kg N/ha. Higher levels of fertilizer nitrogen improved vegetative growth but gave no significant yield increases. Nitrogen applied at sowing was found to be the best time of application for high yields of good quality pods and healthy plant growth. With a preflower application of nitrogen, pods were shorter but pod dry matter yield was better than when applied at sowing. This was in contrast to leaf and stem yields which were higher where N was applied at sowing.

With inoculation, it was found that of the two strains of Rhizobium phaseoli tested, the strain CIAT 161 was very much better than the strain NZP 5232 while the uninoculated control showed no nodulation. Nodule development and nitrogen fixation occurred late in the growing period and was found to start at the onset of flowering. Increasing levels of fertilizer nitrogen caused a decline in nodulation and affected nodule development and subsequent N fixation whether N was applied at sowing or at a later stage of growth.

Although no yield increases occurred due to inoculation in the field, the pot trial showed substantial improvement to both vegetative (60%) and green pod yields (50%). In combination with fertilizer N (80 kg N/ha) inoculation improved vegetative yield significantly but not pod yield.

Beans produced were very dark green. No differences in pod colour with N or inoculation were obtained. Beans produced were much greener than those from Canterbury and Hawkes Bay as measured by the chlorophyll content of pods. High levels of mineral N resulted in very green pods but the amount required cannot be ascertained because of the effect of soil N.