Soil phoshorus(P) uptake mechanisms of chickpea (Cicer arientinum L.)(CP) and pigeonpea (Cajanus
cajan (L.) Millsp) (PP) were studied at ICRISAT, India, from 1983 to 1999 with funds of Tropical Agricultural
Research Center ( present JIRCAS) and Government of Japan Special Project. Earlier in 1983, TARC arrived at
the agreement with ICRISAT to staion younger scientists at ICRISAT hoping to expand their activities to the semiarid
tropics. ICRISAT, on the other hand, expected to increase of research grant from Japan. I was dispatched
to ICRISAT to conduct small reseach project on legume physioligy for three years on October, 1983. However,
the visitation of Diet Member of Japan, Mr. Tsutomu Hata and Mr. Taichi Ohkawara to ICRISAT changed the
the situation. Government of Japan decided to support larger scaled research project at IRRI and ICRISAT. The
renewaled project, called Government of Japan Special Project (GOJ Project), received Dr. Noriharu Ae, Chugoku
Natl. Agric. Expt. Stn. in May, 1985, and Kensuke Okada in December, 1985.
ICRISAT prepared good reseach theme for us. That was to reveal reasons why CP and PP do not respond
to phosphorus application even on soils of very poor phosphorus availability. As both Director General Dr. D L
Windale and Deputy Director General Dr J S Kanwar, ICRISAT are soil scientists and familier with Japanese soil
sciences, they might have expected us to answer the questions.
For the members of GOJ Project, everything on agriculture in the semi-arid tropics was new. We started
fi eld experiments to know how CP and PP grown on Alfi sols and Vertisols. What we decided was to rely on what
we saw and not to rely on literatures. At that time, there were lots of discussions on poor responses of CP and PP
to P application, they were diffusion, root mass, micro nutrients, mychorizae etc. Those theories did not fi t well
with our observations on the several fi eld trials we did.
We decided to start NPK experiments using CP, PP, maize (MZ) and sorghum (SG) on Alfi sols and Vertisols
of poor available P even though most people said it would be useless. NPK trials, however, gave us very valuable
information. CP, MZ and SG grown on Vertisols showed no P defi ciency symptoms. In the SAT area, soil available
P is usually measured with Olsen’s method using alkaline solution, 0.5 M NaHCO3. Available P value with Truog
method, standard method in Japan, contrary uses acidic solution or pH 3.0, gave much higher than Olsen method.
As we already know higher Ca-P content of Vertisols, we estimated CP can lower rhizosphere soil pH close to
pH3.0 with some mechanisms. We later could show CP can lower rhizoshere soil pH close to 3.0 with exuding
organic acid especially citric acid from root surface.
It was a big fi nding for us, as we were confounding with the discrepancy between available P level and
crop growth. Available P level measured with Olsen’s method is higher for Alfi sols than Vertisols. Crops growth,
however, was usually higher on Vertisols than on Alfi sols. With this fi nding, we thought we could well relate crop
growth with available P level. We thought we could answer the question given by ICRISAT.
However, things were not so simple and easy. With NPK pot trials using Alfi sols and Vertisols try to clear
P response curves of several crops, among crops only PP was not responding at all to P applications in Alfi sols,
though it was responding very well in Vertisols. It was very big headache for us. We had to conclude PP could
uptake iron-P with some mechanisms as we know that in most of P exists as iron-P in Alfi sols. From that time, we
started days of discussion for several months.
One morning when we were continuing long tea time discussion, I said PP fl owers scented very fragrant.
Then, Dr. Ae shouted “it must be fl avonoids”. He explained if PP could exude fl abonoids from root surfaces, they
could combine iron and release P from iron bound P. We rushed to the PP fi eld and confi rmed bitterness of the PP
plant and brought back its roots. We prepared agar gel containing iron P reagent and placed PP roots on it. Then gel around roots became clear. After that we started long laborious works with Indian staffs to extract material
which can solubilize iron P and fi nally could get pscidic acid as iron chelating substance. The conclusions at that
time were revealed not complete one. Most important thing of our work, however, is not the identification of
piscidic acid, but the fi ndings of plant capability to actively uptake nutrients from soil.
Along with these studies, we conducted many experiment using PP and CP. From those experiments, we
learned that the active P uptake mechanisms are playing very important role in crop production systems in the
semi-arid tropics. We also realized the limiting factor of crop productivity in the SAT is not the drought but the
low nutrients level of soils, especially P.
Maybe because of the frustration to settle down to international organization and India, we often made
conflicts with ICRISAT. Our intension to keep Japanese style of research might had accelerated crash with
ICRISAT. People around us, Dr. T. Takenaga, agricultural machinery, Dr. C.W. Hong, soil scientists, Korea, and
Dr. K.K. Lee, soil microbiologist, kindly tried to take very good care of us. Management staffs of ICRISAT, Dr.
C. Johansen, leader of Pulse Agronomy, Dr. Y.L. Nene, Director of Legume Department, Dr. Kanwar, DDG and
Dr. Swindale, DG were also paying attention to us. All of them must be worrying about us. In spite of their kind
efforts, we fi nally made the serious confl ict with ICRISAT staffs. One day, DG fi nally called me to his offi ce and
told me to go back home. We didn’t have option to go back home. Option we could take is to stay there. Then we
had serious discussion among us and decided to change our attitude. We also established the manner to cool down
heat of serious discussion among us. That is to take tea break during or after serious discussions or quarrels. Then
we were gradually shaking down with ICRISAT. We also gradually could produce some good results. It was a kind
of surprise for me to see the changes of attitude of ICRISAT staff toward us after we change our attitude toward
ICRISAT. On our last days in ICRISAT, it was our greatest pleasure to receive wards of appraisal from ICRISAT
staff toward our works.
After coming back from ICRISAT, all of us are keeping strong interest in role of root systems in crop
productions. Dr. Ae extended his activities from phosphorus to other nutrients such as nitrogen, cadmium etc.
and has been produced unique and exciting results. Dr. Okada revealed soil acidity itself is not limiting factor of
crop production in highly weathered soils in Colombia. He also showed how to improve productivity of highly
weathered soils with mixed cropping system using acid tolerant rice varieties and tropical grass and leguminous
forages. I also studied crop rotation systems in Hokkaido in relation with mychorizae and soybean production
systems on paddy soils. In both studies I utilized experiences in ICRISAT. Most interesting experience for me is
to fi nd similar types of soils to Vertisols and Alfi sols exist in Japan and learned that there are little differences in
temperate soils and tropical soils.
However, I, maybe Dr. Ae and Dr. Okada too, feel regretful when we think we could not contribute much
to agriculture in the SAT after leaving ICRISAT. In the SAT area, especially in African SAT area, agricultural
productivities continuously declining only because of lack of fertilizers, especially P. Ironically very high
amount of high quality P deposit of African SAT area is exported to developed countries and not utilized locally.
Dr. Bationo, ICRISAT, West and Central Africa, has been conducted many field experiments and showed the
effectiveness of rock phosphate, combined with proper crop rotation systems, in increasing crop production for
longer period than SSP. Dr. Hong, Korea, worked in Ghana in early 1990’s as a member of Global 2000 could
realized in boosting crop production there. I would like suggest Japanese organizations to start a realistic project
based on these achievement to boost agricultural production in SAT.