UNIVERSITY OF NAIROBI College of Agriculture and Veterinary Sciences DEPARTMENT OF PLANT SCIENCE AND CROP PROTECTION

Transcription

1 UNIVERSITY OF NAIROBI College of Agriculture and Veterinary Sciences DEPARTMENT OF PLANT SCIENCE AND CROP PROTECTION Nitrogen fixation and productivity of common bean in phosphorus, nitrogen and moisture stressed soils in the central highlands of Kenya John G. N. Muthamia, P.M. Kimani, G. Cheminingw a, A.O. Esilaba

2 Problem statement Beans production in Kenya is declining fast because producers are poor resource farmers, soil fertility is low in nitrogen and phosphorus and the onward climate change with accompanying terminal or intermittent drought stress.

3 Objectives 1. To determine the effect of phosphorus application on nitrogen fixation and productivity of bush beans and climbing beans. 2.To determine the effect of inoculants on nitrogen fixation and productivity of bush and climbing bean genotypes. 3. To determine the effect of moisture stress on nitrogen fixation and productivity of bush bean and climbing bean genotypes. 4. To determine the significance of genotypes x environment interactions on nitrogen fixation and productivity of bush beans and climbing beans

4 Specific Objective The objective of this experiment was to determine the influence of inoculants: Rhizobium, Azospirillum, Rhizobium+azospirillum coinoculation and no inoculants on climbing bean performance and nitrogen fixation.

5 Materials and Methods Trial site - University of Nairobi-Kabete. Green house Bean Varieties - MAC34 (Kenya Tamu) and MAC64 (Kenya Mavuno) were test bean varieties Gloriabamba nn- Non nodulating reference variety Inoculants: Non inoculation Rhizobium ( CIAT 899) Azospirillum (Azospirillum brasilense sp 245) Rhizobium + Azospirillum (coinoculation) Phosphorus levels (TSP): Zero kg P ha -1 15NCAN (5%15N): Experimental design: 40 kg P ha -1 Starter N and 15N Tracer. Split-split plot design Replications 3. Plants per treatments-5 Hoaglands nutrient solution N and P was used to feed plants in acid

6 Data: Chlorophyll measurement (SPAD) at week 1,2,3,4,5,6,7 and 8 Data analysis: Weekly root length measurements Weekly shoot length measurements Nodule count at 56 DAP Foliage fresh and dry weight Root fresh and dry weight. Root scanning at various depths (cm) (0-5,5-10,10-20,20-40,40-60) Analyse plant tissues for N and P Analyse plant tissues for excess 15N Scanned root analysis to get total root length and volume Genstat statistical package Analysis of variance Means separated using least significant difference (lsd) 95%.

7 2014 Greenhouse inoculant trial Climbing Beans.

8 Inoculant Trial Climbing beans Kabete 2014 Roots are visible

9 Results SPAD Chlorophyll content measurements Bean varieties: No Phosphorus. High Phosphorus GBamba MAC34 MAC 64 GBAMBA MAC 34 MAC LSD 2.92 CV % 5.7.

10 SPAD MEASUREMENTS OF THREE CLIMBING BEAN GENOTYPES GROWN OVER EIGHT WEEKS IN HIGH PHOSPHORUS SAND

11 SPAD MEASUREMENTS OF NON-NODULATING CLIMBING BEAN GROWN OVER EIGHT WEEKS IN HIGH AND LOW PHOSPHORUS SAND

12 SPAD MEASUREMENTS OF MAC34 CLIMBING BEAN GROWN OVER EIGHT WEEKS GROWN ON HIGH AND LOW PHOSPHORUS SAND

13 Influence of Azospirillum, Rhizobium,and coinoculation of Azospirillum and Rhizobium on chlorophyll measurements of Gloriabamba over 8 weeks growth

14 Influence of Azospirillum, Rhizobium and coinoculation of Azospirillum and Rhizobium on chlorophyll content measurements of MAC34 over 8 weeks growth

15 SPAD discussions SPAD measurements of a non-nodulating variety were not affected by inoculants SPAD measurements of N-fixing plants reached minimum in 3 weeks after inoculation (formation and functioning of nodules) SPAD measurements under high P were lower than under low P conditions -more SPAD measurements of non-nodulating plants had gradual decline to the end.

16 Nodule numbers as influenced by phosphorus, variety and inoculants Phosphor us No P Phosphorus Inoculant Azos Control Rhiz Rhi+Azos Azos Control Rhiz Rhiz+Azo s s GBAMBA MAC MAC LSD CV% 108

17 Discussion on nodulation 1. Phosphorus nutrition influenced nodulation of the beans used in this trial. 2. High levels of available P increased nodule numbers. 3. A non-nodulating variety did not respond to P availability and did not nodulate.

18 Shoot dry weight as influenced by phosphorus, inoculants and bean variety and Percent contribution to shoot yield by inoculants Treatment s Phosp horus No Phosphorus Phosphorus Inoculants Azos Control Rhiz Rhiz+A zos Azos Control Rhiz Rhiz+Az os GBamba MAC MAC34 6.6% 0 2.4% 6.8% 8.2% 0 20% 25.7% MAC MAC % 0 18% 29.8% 8.0% % 22.9% LSD 1.13 CV% 29.9

19 Discussions 1. Azospirillum when used on beans in low phosphorus sand was effective in improving biomass yield. 2. Azospirillum when used on beans in high P sand was not effective in improving biomass yield. 3. Rhizobium on low P sand was less effective in improving plant biomass yield. 4. Rhizobium on high P sand was more effective in improving plant biomass yield. 5. Coinoculation of Rhizobium+Azospirillum improved biomass yield significantly at low P sand and high P sand

20 Conclusions 1. Bean seed inoculation with Rhizobium can complement the nitrogenous fertilizer in bean production and yield is maximized under high P conditions 2. Through these experiments it has been shown that Azospirillum can play a vital role of making the scanty soil phosphorus available to beans with subsequent improvement in biomass yield. 3. Coinoculation of Rhizobium and Azospirillum is highly encouraged for these climbing beans because it significantly improved the biomass yields under both high and low phosphorus and under low nitrogen

21 Acknowledgement The National Council for Science Technology and Innovations partially funded this research and is highly appreciated. KU Leuven supplied Azospirillum, Microbial Resource Centre of the University of Nairobi made and supplied the inoculants and Germplasm Resource Unit of CIAT supplied the non- nodulating Gloriabamba nn bean variety.

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