This conference paper has not been peer reviewed. Any opinions stated herein are those of the author(s) and are not necessarily endorsed by or representative of IFPRI or of the cosponsoring or supporting organizations.

Phosphorus use efficiency in amaranth (Amaranthus cruentus L.)

Ojo, O. David1*; Ezekiel, A. Akinrinde3; and Malachy, O. Akoroda3 1National Horticultural Research Institute (NIHORT), PMB 5432, Jericho GRA., Idi Ishin, Ibadan, Nigeria. *Correspondent Cell: +2348023935021; Fax: 234 2412230; Mail:drdavidojo@gmail.com 2Department of Agronomy, University of Ibadan, Ibadan - Nigeria. 3International Institute of Tropical Agriculture (IITA), PMB 5320, Ibadan, Nigeria. Tel.: 234 2412626; Fax: 234 24122221; E-Mail: iita@cgiar.org

SUMMARY Amaranthus cruentus production in the moist savanna of Africa is constrained by low available soil phosphorus (P) while knowledge of P uptake and its utilization for improved Amaranthus cruentus varieties is lacking. Experiments were therefore conducted on the experimental farm of the National Horticultural Research Institute (NIHORT) Ibadan, Nigeria (7°30’N, 30°54’E, 168m above sea level) to evaluate the combined effect of three Amaranthus cruentus varieties (NH84/493, NH84/452 and NH84/445) and four P rates (0, 30, 60 and 90 kg P/ha). The experiment was set up as a 3X4 factorial arranged in randomized complete block design with three replications. Results from the study showed that P use efficiency, P uptake efficiency and P utilization efficiency peaked at 30 kg P/ha and declined thereafter. P use efficiency, P utilization efficiency, and grain produced per gram of applied P were significantly different among varieties in the order NH84/493> NH84/445> NH84/452. Grain yield among the varieties is in the following order NH84/493> NH84/445> NH84/452. Grain yield peaked at 30 kg P/ha irrespective of varieties. We conclude therefore that, grain yield, P use efficiency and its components were highest at 30 kg P/ha and variety NH84/493 potentially utilizes P best compared to others.

________________________________________________________________________Key words: Phosphorus, use, efficiency, utilization, harvest index, amaranth

INTRODUCTION

Grain amaranth (Amaranthus cruentus L.) belongs to the family Amaranthaceae with over 800 species (Grubben, 1976). The seed of grain amaranth is important for its relatively high nutritive value especially protein content compared to major food grains like maize, wheat, oat, barley and rye (Luis, 1992). It is processed into many food items, supplements and additives (Bressani, 1988, 1989; Akingbala et al., 1994; Dehiya and Kapoor, 1994; Ojo et al. 2007). Industrially, grain amaranth could be used in the production of vegetable ink and the stover can be processed into animal feed. It is drought tolerant and highly adaptable to the tropics as a potential crop (Piha, 1995). It is thus important for diversifying and improving the food basket thereby contributing to food security of the sub-Saharan African region, where per capita food production has steadily declined over the past three decades (IBRD, 1989).

Tropical soils are often low in available phosphorus (P) and therefore require its application for optimum crop growth and yield, especially for rapidly growing annual crops such as grain amaranth (Pritchett, 1976; Kanabor, 1978; Mokwunye, 1979; 1981; Zapata and Axmann, 1995; Casanova, 1995; Manske et al. 2002; Ojo, et al. 2007). Over US$100 million is spent on conventional, water soluble P fertilizers in Nigeria annually (Sobulo, 1992). The high cost of these conventional P fertilizers constrains their use by resource-poor farmers (Bationo et al., 1986; Hammond, 1986; Lombin, 1987).

Production of grain amaranth grain ranges from 3 to 3.5 tons/ha in California, 3.0 tons/ha in India; and in Nigeria between 0.3 to 1.5 tons/ha which is low (NIHORT, 1995). The relatively low yield in Nigeria is attributed to environmental factors including low phosphorus status in the soil (Balasubramanian et al., 1978; Adepetu, 1981; Agboola and Sobulo, 1981; Ataga and Omoti, 1987).

Grain amaranth has high P requirement and therefore responds to P application (Gupta and Thimba, 1992). Its productivity can be improved at reduced cost through combined use of low-cost PR and the selection of grain amaranth varieties with high efficiency for uptake and utilization of P from soil. While varietal differences in efficiency of P uptake from soil has been studied for some crop species such as maize (Adetunji, 1995), these studies are lacking in grain amaranth. Such information would be useful for identification selection and subsequent development of breeding programmes genotypes with high capabilities for using P in low-P soils.

Improved and selected grain amaranth varieties (NIHORT, 1984; 1995) are known to exhibit variation with respect to grain quality, yield and disease tolerance. However, very little is known about their P requirements, uptake, and utilization. It is probable that the differential performance exhibited by the selected grain amaranth varieties might partly be a function of their P uptake, utilization and physiological functions in the crop tissues (NIHORT, 1995). Based on these premises the present study was carried out with the objective to determine the phosphorus use efficiency of grain amaranth.

MATERIALS AND METHODS

The study was conducted during two consecutive cropping seasons in 1999 at the vegetable experimental plots of the National Horticultural Research Institute of Nigeria (NIHORT), Ibadan (latitude 7°30'N and longitude 3°54'E, 168 meter above sea level), Nigeria. Ibadan lies in the forest-savanna zone with a bimodal rainfall distribution which peaks in June/July and September. This distribution creates two cropping seasons generally categorized as early and late. The early rain occurs between late March/early April and end of July while the late rain occurs from August/September to November. There is a characteristic dry spell in August before the late rain commences. The dry season is from November to March. During the study period, Ibadan had a mean annual rainfall of 1210mm (Table 1). Annual temperature at the location ranges from an average minimum of 21°C to a mean maximum of 32°C while mean monthly relative humidity ranges between 61% and 83% (NIHORT, 1995).

Soil samples taken were air-dried for 5 days under ambient temperature, ground, sieved through a 2mm-sieve, and analysed for their various physico-chemical properties including total nitrogen, pH, organic carbon, available P, exchangeable Ca, K, Mg, Na, Fe, Mn and Al. The procedures used were according to IITA (1976). Total nitrogen and organic carbon were determined by the Kjeldahl (Bremer, 1965) and Walkey and Black procedures (Nelson and Sommers, 1982), procedures respectively. Soil pH was measured using a 1:2 (W/V) soil water suspension ratio. Available phosphorus was analysed by the Bray P-1 method (Bray and Kurtz, 1945). Potassium, Ca and Mg were first extracted using neutral normal NH40Ac (IITA, 1976). Thereafter, K was determined by flame emission in the Perkin-Elmer 5000 Atomic absorption spectrophotometer; Mg and Ca by atomic absorption; other exchangeable bases according to Jackson, 1958; and CEC was determined as the sum of exchangeable bases and exchangeable acidity (Juo and Fox, 1977). The mechanical analysis was carried out by the hydrometer method (Bouyoucous, 1951).

The three grain amaranth varieties, NH84/445, NH84/452 and NH84/493, used in the study were obtained from the Genetic Resource and Biotechnology Division of NIHORT (Table 2). These varieties had been shown to differ in grain yield, seed color, plant coloration and disease tolerance (NIHORT, 1984; 1995).

The experimental design was a 3 x 4 factorial arrangement in a randomized complete block. Three grain amaranth varieties NH84/445, NH84/452 and NH84/493 in combination with four levels of phosphorus: 0, 30, 60 and 90 kg P ha-1 formed the 12 treatment combinations per replicate. There were four replications.

The field was ploughed and harrowed before the fertilizer was broadcasted according to treatments and then manually incorporated into the soil using hand-hoe. Seeds were drilled at 25cm spacing in 50cm wide rows at the rate of 5kg ha-1 on the 15th April and 27th August 1999 and later thinned to one plant per stand two weeks later (NIHORT, 1984; 1995). This gave a plant population of 80,000 ha-1. There were 10 rows per plot and each row was 5m long. Net plot size was 25m2.

Fertilizer Application

Basal application of 60 kg ha-1 of nitrogen and potassium as calcium ammonium nitrate (CAN) and muriate of potash (MOP) respectively were done at 2 WAP by incorporation into the soil. The phosphorus was applied at planting using single super phosphate (SSP) as indicated earlier (NIHORT, 1984; 1995).

Weed and Pest Control

Hand weeding was done at 2, 5 and 8 WAP. Cypermethrin at 50g a.i. per hectare was sprayed against insects, starting from 3 WAP and at forth-nightly interval until 9 WAP. Bynomyl as Benlate at 150g a.i. per hectare was applied to control fungal attack starting from 3 WAP and fortnightly till 9 WAP.

Data Collection

Grain amaranth whole plant samples were taken at 3 weeks interval starting at 3 WAP to 18 WAP. Five plants were randomly sampled per plot from two rows bordering the centre rows. A final sample was taken at physiological maturity (18 WAP). The inflorescence was processed to separate the grain from the shaft, the grain was then weighed.

Plant Sample Preparation and Laboratory Analysis

At maturity (18 WAP), five representative plants were harvested and separated into grain, leaf, stem and root. The samples were dried at 75°C for 48 hours. The grain was ground in Wiley mill of 2mm-mesh and analyzed for percent P in grain at IITA (IITA, 1976).

Determination of Components of Phosphorus Use Efficiency

Phosphorus use efficiency is defined as a ratio of grain produced to available P in the soil (Chapin, 1987; Cooke, 1987) and is expressed as:

PUE = PUPE x PUTE .................................... (1)

in which,

PUE = Phosphorus use efficiency (Gw/Ps)

PUPE = P uptake efficiency (Pt/Ps)

PUTE = P utilization efficiency (Gw/Pt)

The above relationship is also expressed as:

Gw/Ps = (Pt/Ps) x (Gw/Pt) ............................. (2)

in which,

Gw = grain yield (g plant-1),

Ps = total soil P supply (g plant-1), and

Pt = total plant P (g plant-1)

The term PUTE could also be expressed as:

PUTE = GPE x PHI

in which,

GPE = ratio of grain weight and grain phosphorus (Gw/Pg)

PHI = phosphorus harvest index (Pg/Pt)

The above relationship is also expressed as:

Gw/Pt = (Gw/Pg) x (Pg/Pt) .............................. (3)

in which,

Pg = amount of phosphorus in the grain (g/plant)

Statistical Analysis

Analysis of variance was carried out based on the randomized complete block (RCB) design as earlier stated (Steel and Torrie, 1981). Direct treatment effects and the magnitude of interactions were determined. Treatment means were compared using Duncan’s Multiple Range Test (DMRT).

RESULTS

The chemical and physical properties of the soils used for the study before cropping are presented in Table 3. The soil pH was 4.9 (acidic) and 5.7 (slightly acidic) in the early and late raining seasons of 1999, respectively. The organic carbon content in the early season was lower (3.3g/kg) than that of late season (3.9g/kg). Total N of 0.49g/kg was higher for late season than 0.42g/kg in the early season. The available P (Bray P1) was 3.7 mg/kg in the first season and 4.3 mg/kg in second season of 1999. The available Ca was low at both sites considering that 2.5 cmol/kg was the critical level. However, exchangeable Mg and K were adequate in both soils considering critical level of 0.2 cmol/kg (Adeoye et al., 1985). Total acidity was about the same in both sites. Effective cation exchange capacity was higher in the late season soil with 3.56 cmol/kg than in the early season soil with 2.38 cmol/kg. The early season soil was more sandy with lower silt and clay content compared with the late season soil. The soils of both sites have been classified as alfisols (Harpstead, 1973).

Grain yield

In both seasons of study, increased P rate significantly increased grain yield till 30kg P/ha thereafter yield fell though not significantly (Table 4). The pattern of decrease in grain yield among varieties was consistent in both season and was of the order NH84/493> NH84/445> NH84/452 (Table 4).

Phosphorus use efficiency Effect of P rates on P accumulation parameters

In both seasons, P application significantly affect P accumulation in the dry matter of leaves and total plant parts at 4, 9 and 15WAP; Stem and root at 9 and 15WAP;

and grain at harvest (Table 5). Phosphorus uptake in leaf significantly increased up to 30kg P/ha at 4WAP in both seasons, at 9WAP in the early season and 15WAP in the late season and up to 60kg P/ha at 15WAP in the early season. Phosphorus accumulation in leaf dry matter at 9WAP in the late season followed the order 60kg P>90 kg P >30 kg P >0kg P. Stem and root P uptake increased up to 60kg P/ha thereafter it declined in first season and second season. In the grain all P rates resulted in higher P accumulation than no P in the two seasons, 60kg P/ha caused higher P accumulation than 90kg P/ha in the late season (Table 5). Phosphorus accumulation in the different plant parts among varieties were not significantly different at 4 WAP in both seasons (Table 6). Varieties however differed significantly in P accumulation in stem and total dry matter at 50% anthesis which corresponded to 9 WAP where it followed the order NH84/452> NH84/445> NH84/493 in both seasons except early season for total dry matter with equal P for NH84/445 and NH84/493. There were significant differences among varieties in both seasons at 15 WAP for P accumulation parameters except for grain P uptake in the late season. Phosphorus uptake was lower in the first season than in the second season (Table 6). There were no significant differences in variety by P rate interaction in 1999 data were therefore not presented. Main effect of P on P-use efficiency and components of P-use efficiency

In both seasons of study, P-use efficiency (PUE) and its components – P uptake efficiency (Pt/Ps), P utilization efficiency (Gw/Pt) and grain yield/grain P (Gw/Pg) – were significantly affected by P rates (Table 7). P-use efficiency (Gw/Ps), P uptake efficiency (Pt/Ps) and P utilization efficiency (Gw/Pt) decreased significantly with increased P rates in the two seasons. P application similarly depressed P utilization efficiency (Gw/Pt) and Grain produced per unit P (Gw/Pg) in both seasons. Phosphorus harvest index (Pg/Pt) was not significant among P rates in both seasons of study (Table 7).

Effect of varieties on P-use efficiency and components of P-use efficiency

P-use efficiency, P utilization efficiency and grain produced per unit gram P were significantly different among the amaranth varieties at both seasons of 1995 (Table 8). P uptake efficiency was significant at early season. P harvest index (Pg/Pt) and P uptake efficiency were not significant in the late season. P-use efficiency, P utilization efficiency, and grain produced per unit of gram P (Gw/Pg) were of order NH84/493> NH84/445> NH84/452 among varieties (Table 8).

Interactions of P x variety and season x P x variety were not significant data were therefore discarded.

DISCUSSION

Several factors affect rate of phosphorus (P) dissolution and their P availability to plants (Manske et al. 2002; Osborn et al. 2002; Ojo et al. 2007). Availability of P to plant depends on their rate of dissolution which is dependent on soil characteristics, the plant, as well as fertilizer management factors (Obigbesan and Mengel 1981ab; 1982; Porter and Sanchez, 1992; Rajan et al. 1996; Iyamuremje et al. 1996; Conny, 1998; Daniel et al. 1998; Daniel et al. 1999; Philip and Stephen, 1999).

The pre-cropping soil available P status of experimental sites in 1999 (Table 3) which ranged between 3.7 to 4.3 mg P/kg was lower than critical level of 13mg P/ha suggested by Sobulo et al., 1981 and Adeoye et al., 1985; indicating deficiency level. This characteristically low P soil status confirms the appropriateness of the site of the experiment. These observations are corroborated by several workers who reported that most Nigerian soils, like others found in the tropics, exhibit P deficiency which sharply decrease yield of agricultural crops (Balasubramanian et al. 1978; Adepetu, 1981; Agboola and Sobulo, 1981; Obigbesan et al. 1982; Ataga and Omoti, 1987; Adediran and Sobulo, 1998).

Although non significant, the increase in soil pH with increasing P rate may be due to direct P effect on soil and stressed the fact that P fertilization enhances plant uptake of cations Ca, Mg, K, Na as well as N. As the soil is gradually depleted of Ca due to increased plant uptake, P rate and crop growth the soil acidity increases because reduced Ca content increases acidity and vice versa. Effective utilization of P by some plant species (e.g. buckwheat and rape) has been attributed to this charactaristically high Ca uptake (Flach, 1987, Bekele et al. 1993; Singaram, 1995; Illenseer et al. 2002; Abichequer et al. 2003; Dwivedi et al. 2003; Shenoy et al. 2005). Plant roots may also excrete organic acids which can be expected to lower rhizosphere soil pH thereby increasing soil acidity (Hoffland, 1989).

Grain yield significantly increased with increasing P rates up till 30kg P/ha, thereafter further P application was not significant in increasing grain yield. The observed increase in the grain yield with increasing P supply might be attributed in part to the inherently low P status of the soil used in this study. Among the environmental factors that interact in the field with a crop, phosphorus is perhaps the most important of the nutrients because of its metabolic role and its requirement in large quantities by plants. It initiate photosynthetic reactions of splitting water molecule by light energy in the presence of adenosine diphosphate (ADP) and then the subsequent fixing of carbondioxide (Daniel, 1998). This process ultimately results in photosynthetic assimilate in plant tissues. The association of higher grain yields over P rates with amaranth in this study was in accordance with results of Bly and Woodard, (1997); Didier and El-Sharkawy, (1993); Adediran and Sobulo, (1998); Singh et al. 2005. The decline in grain yield after 30kg P/ha indicated that optimal P was reached. Generally,

considering soil P sorption, precipitation and loss of P by rainfall or leaching, fertilizer application management and other factors 50kg P/ha is recommended for the soil used in this study. Higher optimal P was recorded in the first season over the second season probably due in part to the low pre-cropping P fertility status of the first season soil compared with the second season soil (Table 3). Specifically, soil lower in P status will require more P supply to reach optimal P than soil higher in P fertility status. Grain yield decreases among varieties observed in this study corroborate findings described by Daniel (1999), Didier and El-Sharkawy (1993); Tollenaar (1986, 1989, 1991); Sanginga et al. 2000; Abichequer et al. 2003 as earlier highlighted that hormonal, physiological and other genetic factors are responsible for yield differences.

Phosphorus use by amaranth is a complex trait. It consists of numerous physiological components such as uptake, translocation, assimilation and redistribution (Daniel et al. 1998). Each of these components is likely to be the result of the action of many genes. In addition each of the components has a response curve to environmental factors (temperature, water stress, light) and to cultural practices (plant density, other nutrients, crop genotypes). Therefore, varieties may differ, not only in the genetic make up that results in the ability to take up and use P, but in the way that the genetic make up is influenced by the environment. As a result, any given variety’s response to P is difficult to predict and highly dependent on the growing environment.

In this study, differences were observed for P accumulation parameters as well as P use efficiency parameters. The differences were more apparent in second season of when P requirement was higher due to higher grain yields. Generally, total P uptake as well as grain P uptake were significantly increased with increased P at least up to 30kg P/ha. Variations in consistency were attributed to environmental instability and/or influences such as rainfall, sunlight, cloud cover and even crop factor such as fungal disease infection influences. The effect of environmental factors are strongly related to P accumulation and efficiency since plants in the control plot (no P) in the second season accumulated at times twice as much P as plants with no P in the first season at harvest (18 WAP). The low P accumulation in the first season could probably be due in part to inherent low fertility status of the soil.

P-use efficiency (PUE), and its components – P uptake efficiency (PUPE), P utilization efficiency (PUTE), and grain yield per unit grain P (Gw/Pg) – decreased with increasing P rates in both seasons of this study. This result is in agreement with the trend observations of Akintunde et al. 1993; Bundy and Carter, 1988; Sabata and Mason, 1972 who reported a decrease in value of N use efficiency and N utilization efficiency with each additional N increase. Decrease in PUE and its components are expected for higher P rates applications to maximize grain yield. Our result indicated that P-use efficiency and P uptake efficiency at 30kg P/ha were more than twice the values obtained for these traits at 60kg P/ha at least in second cropping season, suggesting that under low supply of P, the physiological efficiency of amaranth plants to produce a certain quantity of grain from every gram of P applied is increased while as more P was supplied the tendency was for the amaranth plants to reduce the amount of grain produced per gram of P.

The low values of P-use efficiency in first season compared to second season as observed in this study, are primarily related to the low harvest index for the first cropping season. The low P harvest index observed in this study could be related to the lower levels of pre-cropping soil P of most Nigerian soil used in the study.

Differences in P-use efficiency and its components were observed among amaranth varieties were in this study. Again, variety NH84/ 493 was more efficient in PUE, PUTE and Gw/Pg than NH84/452 and NH84/445. This appeared to be due to the genetic capability of NH84/493 to absorb and utilize more P from the soil for grain production than varieties NH84/452 and NH84/ 445. In general, higher values of P uptake efficiency were recorded in the second season than in the first season, this we attributed was due in part to the lower pre-cropping soil P status in the first season compared to the second season.

REFRENCES Abichequer, A. D. , Bohnen, H. , and Anghinoni, I. 2003. Phosphorus uptake,

translocation and utilization in wheat varieties under aluminium toxicity. Revista Brasileira de Ciência do Solo, 2003, Vol. 27, No. 2, pp. 373-378.

Adediran, J.A. and R.A. Sobulo. 1998. Agronomic evaluation of phosphorus fertilizers developed from Sokoto Rock Phosphate in Nigeria. Communication in Soil Science and Plant Analysis, 29(15 & 16): 2415-2421.

Adeoye, G.O. and Agboola, A.A. 1985. Critical levels of soil pH, available P, K, Zn and Mn and maize ear leaf content of P, Cu, and Mn in sedimentary soils of South Western Nigeria. Fertilizer Research, 6(1): 65.

Adepetu, J.A. 1970. The relative importance of organic P to crop nutrition in soils of Western Nigeria. M.Phil. thesis, University of Ife, Ile-Ife, Nigeria.

Adepetu, J.A. 1975. Evaluation of kinetic process involved in phosphorus availability to plant root in soil. Ph.D. dissertation. Purdue University, West Lafayette, IN. U.S.A.

Adepetu, J.A. 1981. Characteristics P sorption and its implications in soils of Ondo State of Nigeria. Journal Tropical Agriculture Veterinary Science, 19(5): 291-300.

Adepetu, J.A. 1983. Phosphorus fertilization of tropical crops. In: Nutrient supply to tropical crops. Enzman, Mutcher and Frank (ed.) Institute of Tropical Agriculture, Leipzing Publisher, pp.211-238.

Adepetu, J.A. 1986. Soil fertility and fertilizer requirement in Oyo, Ogun and Ondo States. Federal Ministry of Agriculture and Water Resources, Lagos, Nigeria.

Adepetu, J.A., A. Adebayo, E.A. Aduyi and C.O. Alofe. 1979. A preliminary survey of the fertility status of soils in Ondo State under traditional cultivation. Ife Journal of Agriculture, 1(2): 134-149.

Adetunji, M.T. 1995. Equilibrium phosphate concentration as an estimate of phosphorus needs of maize in some tropical Alfisols. Tropical Agriculture (Trinidad), 72(4):12-17.

Agboola, A.A. and R.A. Sobulo 1981. A review of soil fertility in Southwestern zone of Nigeria. Report No. 6. Federal Department of Agriculture and Land Resources, Kaduna, Nigeria, pp. 1- 35.

Akingbala, J.O., Adeyemi, J.A., Sangodoyin, S.O. and Oke, O.L. 1994. Evaluation of amaranth grains for ogi manufacture. Plant Foods for Human Nutrition, 46(1): pp. 1926.

Akintunde, A.Y., Obigbesan, G.O. and S.K. Kim. 1993. Nitrogen use efficiency and grain yield as influenced by nitrogen fertilization and hybrid maize varieties in Nigeria. pp.119-124. In: M.A.B. Fakorede et al. (eds), Maize Improvement, production and utilization in Nigeria. Published by Maize Association of Nigeria.

Ataga, D.O. and Omoti, U. 1978. Phosphate sorption characteristics and the use of sorption isotherms for evaluating the phosphorus requirement of the oil palm on some acid soils. Journal of Nigerian Institute of Oil Palm Research, 5: 37-47.

Ataga, D.O. and U. Omoti.1987. Fertilizer use on palms in Nigeria. pp. 175-193. In: R.A. Sobulo et al (eds.). Towards Efficiency of Fertilizer Use and Development in Nigeria. Proceedings of the National Fertilizer Seminar, Oct. 28-30, Port Harcourt, Nigeria.

Balasubramanian, V., L.A. Nnadi, L.G. Lombin, and V.A. Yayock 1978. Fertilizer use in Nigeria. II. Future Prospects and Problems. Samaru Conference Paper No. 32. Samaru, Nigeria.

Bationo, A., S.K. Mughogho, and A.U. Mokwunye. 1986. Agronomic evaluation of phosphate fertilizers in tropical Africa. pp. 283-318. In: A.U. Mokwunye and P.L.G. Vlek (eds.). Management of N and P fertilizers in sub-Saharan Africa. Martinus Nijhoff, Dordrecht, The Netherlands.

Bekele, T. and Hofner, W. 1993. Effect of different phosphate fertilizers on yield of barley and rape seed on reddish brown soils of the Ethiopian highlands. Fertilizer Research, 34: 243-250.

Bly, A. and H.J. Woodard. 1997. Soybean growth and yield response to residual fertilizer P. bands. Journal Plant Nutrition, 20(11): 1527-1537.

Bouyoucous, G.J. 1951. A recalibration of hydrometer method for making mechanical analysis of soils. Agronomy Journal, 43: 434-438.

Bray, H.R. and Kurtz, L.J. 1945. Determination of total organic and available phosphorus in soils. Soil Science, 59: 39-41.

Bremer, J.M. 1965. Total Nitrogen. In: Method of Soil Analysis, Black, C.A. (ed.). Agronomy 9: American Society of Agronomy, Madison, Wisconsin. pp. 1141-1174.

Bressani, R. 1988. Amaranth: the nutritive value and potential uses of the grain and by-products. Food and Nutrition Bulletin, 10(2): pp.49-59.

Bressani, R. 1989. The protein of grain amaranth. Food and Nutrition Bulletin, 5(1), pp.13-38.

Bressani, R. and L.G. Ellias .1986. Development of 100% amaranth foods. In "Proceedings of the Third Amaranth Conference". Rodale Press, Emmaus, PA.

Bressani, R., J.M. Gonzales, J. Zuniga, M. Breuner, and L.G. Elias. 1987. Yield, selected chemical composition and nutritive value of 14 selections of amaranth grain representing four species. Journal of the Science of Food and Agriculture, 38(4): 347-356.

Bundy, L.G. and Carter, P.R. 1988. Corn hybrid response to nitrogen fertilizer in the Northern Corn Belt. Journal of Production Agriculture, 1: 99-104.

Casanova, E.F. 1995. Agronomic evaluation of fertilizers with special references to natural and modified phosphate rock. Fertilizer Research, 41(3): 211-218.

Chapin, F.S. 1987. Adaptations and physiological responses of wild plants to nutrient stress. In: H.W. Gabelman and B.C. Loughman (editors), Genetic Aspects of Plant Mineral Nutrition. Martinus Nijhoff Publishers, Dordrecht, pp. 15-25.

Conny, W.H. 1998. Response of phosphorus during vegetative and reproductive phases. Journal of America Society of Horticultural Science, 123(2): 215-233.

Cooke, G.W. 1987. Maximum fertilizer efficiency by overcoming constraints. Journal of Plant Nutrition, 10: 1357-1369.

Daniel, E.D., Kazuhiro, O. and Moritaka, S. 1999.Dissolution of phosphate rock fertilizers in some soils of Japan. Australian Jour. Soil Research, 37: 115-122.

Daniel, P.S., Robert, J.R. and S.M. Ayling. 1998. Phosphorus uptake by plants: From soil to cell. Plant Physiology, 116: 447-453.

Dehiya, S. and Kapoor, A.C. 1994. Acceptability and viscosity of low cost home processed supplementary foods developed for pre-school children. Plant Foods for Human Nutrition, 46(4): 257-297.

Dehiya, S. and Kapoor, A.C. 1995. Acceptability and viscosity of low cost home processed supplementary foods developed for pre-school children. Plant Foods for Human Nutrition, 47(1), pp.1-12.

Didier, P. and El-Sharkawy, M.A. 1993. Cassava varietal response to phosphorus fertilization. II. Phosphorus uptake and efficiency. Field Crop Research, 35: 1-20.

Dwivedi, B. S. , Shukla, A. K. , Singh, V. K. , and Yadav, R. L. 2003. Improving nitrogen and phosphorus use efficiencies through inclusion of forage cowpea

in the rice-wheat systems in the Indo-Gangetic Plains of India. Field Crops Research, 2003, Vol. 80, No. 3, pp. 167-193.

El Sharkawy, M.A., R.S. Loomis and W.A. Williams . 1968. Photosynthetic and respiratory exchanges of carbondioxide by leaves of grain amaranth. Journal Applied Ecology, 5(1): 243-251.

Flach, E.N. 1987. A comparison of the rock phosphate-mobilizing capacities of various crop species. Tropical Agriculture, 64: 347-352.

Grubben, G.J.H. 1976. The cultivation of amaranth as a tropical leaf vegetable with special reference to South Dahomey. Communication in the Department of Agricultural Research, Royal Tropical Institute (Netherlands). No. 67, 207pp. 1-206.

Grubben, G.J.H. 1977. Amaranthus. In Tropical vegetables and their genetic resources, Edited by H.D. Tindall and J.T. William. Roman International Board for Genetic Resources, pp. 96-101.

Gupta, V. K. and Thimba, D. 1992. Grain amaranth: A promising crop for marginal areas of Kenya. Food Reviews International, 8(1), 51-69.

Hammond, L.C. 1986. Agronomic value of unacidulated and partially acidulated phosphate rocks indigenous to the tropics. Advance Agronomy, 40: 89-140.

Harpstead, R.L., J.M. Lapense and K.C. Ivarson. 1973. Mineralization of soil organic phosphorus with particular reference to the effect of lime. Canadian Journal of Soil Science, 43: 97-106.

Hoffland, E. 1989. Solubilization of rock phosphate by rape. II. Local root exudation of organic acids as a response to P-starvation. Plant Soil, 113: 161-165.

IBRD (International Bank for Reconstruction and Development) .1989. Sub-saharan Africa: From Crisis to sustainable growth, a long-term perspective study. World Bank, Washington, D.C., U.S.A.

IITA (International Institute of Tropical Agriculture). 1976. Automated and Semi-automated methods for soil and plant analysis. Manual Series No. 7, IITA, Ibadan, Nigeria.

Illenseer, R. and Paulilo, M. T. S. 2002. Growth and nutrient use efficiency in Euterpe edulis Mart. seedlings under two levels of irradiance, nitrogen and phosphorus. Acta Botanica Brasilica, 2002, Vol. 16, No. 4, pp. 385-394.

Iyamuremje, F.I. and R.P. Dick. 1996. Organic ammendments and phosphorus sorption by soils. Advances in Agronomy, 56 pp.139-185.

Jackson, M.K. 1958. Soil chemical analysis. Prentice Hall, Inc., Englewood Cliffs, NJ.

Juo, A.S.R. and R.L. Fox. 1977. Phosphate sorption characteristics of some benchmark soils of West Africa. Soil Science, 124: 370-376.

Kanabor, R.H. 1978. Phosphorus absorption by surface samples of 5 iron pan soils of Ghana. Geoderma, 20: 299-306.

Lombin, G.L. 1987. Fertilizer requirements of major cereal crop in the Nigeria savanna. pp. 106-126. In: R.A. Sobulo et al. (eds.). Towards Efficiency of Fertilizer Use and Development in Nigeria. Proceedings of the National Fertilizer Seminar, Oct. 28-30, Port Harcourt, Nigeria.

Luis, S.K. 1992. Grain amaranth research in Peru. Food Reviews International, 8(1): 87-124. Manske, G. G. B. , Ortiz-Monasterio, J. I. , Ginkel, R. M. van , Rajaram, S. , Vlek, P. L. G.2002. Phosphorus use efficiency in tall, semi-dwarf and dwarf near-isogenic lines of spring wheat. Euphytica, 2002, Vol. 125, No. 1, pp. 113-119.

Mokwunye, A.U., S.H. Chien, and E. Rhodes. 1986. Phosphorus reaction with tropical African soils. pp. 253-281. In: A.U. Mokwunye and P.L.G. Vlek (eds.). Proceedings of the Symposium on Management of Nitrogen and Phosphorus Fertilizers in sub-Saharan Africa, March 25-28, 1985. Lome, Togo.

Mokwunye, U. 1979. Evaluation of three phosphate sources applied to maize at Samaru. Tropical Agriculture (Trinidad), 56: 65-68.

Mokwunye, U. 1981. Phosphorus fertilizers in Nigerian Savanna Soils. Samaru Journal of Agricultural Research, 1(2): 103-109.

Nelson, D.W. and Sommers, L.E. 1982. A simple digestion procedure for determination of total nitrogen in soils and sediments. Journal of Environmental Quality, 1: 423-425.

NIHORT (National Horticultural Research Institute) .1984. NIHORT Annual Report, NIHORT, Ibadan, Nigeria.

NIHORT (National Horticultural Research Institute) .1995. NIHORT Annual Report, NIHORT, Ibadan, Nigeria.

Obigbesan, G. O., Agboola, A. A., and Fayemi, A. A. 1982. Nitrogen and phosphate fertilizer needs of cultivated yams species in the Savanna zone of western Nigeria. Nigeria Agriculture Journal, 17/18(1982): 129 – 140.

Obigbesan,G.O. and Mengel, K.1981a. Use of electroultrafiltration method for investigating the behaviour of phosphate fertilizers in tropical solis. Fertilizer Research, 2: 169-176.

Obigbesan,G.O. and Mengel, K.1981b. Relationship between electroultrafiltration extractable phosphorus, P-uptake, and P buffer capacity of selected tropical soils. Nigerian Journal of Soil Science, 1(1): 1- 12.

Ojo, O. David, Abiodun, A. Kintomo, Ephraim, A. Akinride and Malachy, O. Akoroda. 2007. Comparative effects of phosphorus sources for grain amaranth production. Communication in Soil Science and Plant Analysis, 38: 1 – 21 (2007).

Osborne, L. D. , Rengel, Z.2002. Genotypic differences in wheat for uptake and utilization of P from iron phosphate. Australian Journal of Agricultural Research, 2002, Vol. 53, No. 7, pp. 837-844.

Pant, K.C. 1985. Effect of heat processing (popping) on protein nutritional quality of grain amaranth. Nutrition Reviews International, 32: 1089-1098.

Philip, M.H. and Stephen, C.J. 1999. Transfer of phosphorus from agricultural soils. Advances in Agronomy, 66: 195-201.

Piha, M.I. 1995. Yield potential, fertility requirements, and drought tolerance of grain amaranth compared with maize under Zimbabwean conditions. Tropical Agriculture, 72(1): 7-12.

Porter, P.S., and Sanchez, C.A. 1992. The effect of soil properties on phosphorus sorption by everglades histosols. Soil Science, 154: 387-398.

Pritchett, W.L. 1976. Phosphorus in forest soils. Phosphorus in Agriculture. No. 67, pp. 27-35.

Rajan, S.S.S., Connor, M.B. and Sinclair, A.g. 1994. Partially acidulated phosphate rock: controlled release P fertilizers for more sustainable agriculture. Fertilizer Research, 37: 69-78.

Rajan, S.S.S., Fox, R.L., Saunders, W.M.H. 1991. Influence of pH, time and rate of application on phosphate rock dissolution and availability to pasture. I. Agronomic benefits. Fertilizer Research, 28: 95-101.

Rajan, S.S.S., J.A. Wakinson, A.G. Sinclair. 1996. Phosphate rocks for direct application to soils. Advances in Agronomy, 57 (1996): 77-121.

Sabata, R.I., and Mason, S.C. 1992. Corn hybrid interactions with soil nitrogen levels and water regime. Journal of production agriculture, 5: 137-142.

Sanginga, N. , Lyasse, O. , Singh, B. B.2000. Phosphorus use efficiency and nitrogen balance of cowpea breeding lines in a low P soil of the derived savanna zone in West Africa. Plant and Soil, 2000, Vol. 220, No. 1/2, pp. 119-128.

SAS Institute. 1988. SAS User's Guide, SAS Institute, Cary, N.C., U.S.A.

Shenoy, V. V. and Kalagudi, G. M.2005. Enhancing plat phosphorus use efficiency for sustainable agricultrure. Biotechnology Advances, Vol. 23, No. 7/8, pp. 501-513.

Singaram, P. 1995. Phosphate rock and phosphate rock mixture as fertilizer for crops grown on calcerrous soils. Communication in Soil Science and Plant Analysis, 26: 1571-1593.

Singh, K. K. , Srinivasarao, C. and Masood Ali. 2005. Root growth, nodulation, grain yield, and phosphorus use efficiency of lentil as influenced by phosphorus, irrigation, and inoculation. Communications in Soil Science and Plant Analysis, 2005, Vol. 36, No. 13/14, pp. 1919-1929.

Sobulo, R.A. 1992. Evaluation of Sokoto Rock Phosphate as phosphorus source in Nigerian soils. National Fertilizer Company of Nigeria (NAFCON), Port Harcourt, Nigeria.

Sobulo, R.A. 1994. Final report on agro-mineral project. Raw Materials Research and Development Council (RMRDC) and National Fertilizer Company of Nigeria (NAFCON), Port Harcourt, Nigeria.

Sobulo, R.A., and Osiname, A.O. 1981. Soils and fertilizer use in Western Nigeria. Research Bulletin No. 11 Institute of Agricultural Research and Training, University of Ife, Nigeria.

Steel, R.G., and Torrie, J.H. 1981. Principles and procedures of statistics. McGraw-Hill Book Co., New York.

Tollenaar, M. 1986. Environmental influences on development of sinte potential, kernel set and fill. pp.21-23. In. J.C. Shannon et al (ed.). Regulation of carbon and nitrogen reduction and utilization in maize. American Society of Plant Physiology, Rockville, M.E.

Tollenaar, M. 1989. Genetic improvement in grain yield of commercial maize hybrid grown in Ontario from 1959 to 1988. Crop Science 29, 1369-1371.

Tollenaar, M. 1991. Physiological basis of genetic improvement of maize hybrids in Ontario from 1950 to 1958. Crop Science, 31: 119-124.

Tollenaar, M.1991. Physiological basis of genetic improvement of maize hybrids in Ontario from 1950 to 1988. Crop Science, 31: 119-124.

Zapata, F. and Axmann, H. 1995. Isotopic techniques for evaluating the agronomic effectiveness of rock posphate materials. Fertilizer Research, 41: 3, 189-195.

Table 1: Monthly rainfall (mm) and number of rain days at Ibadan (1999). Rain Rain fall days January 0.0 0 February 1.0 1 March 143.0 8 April 173.7 9 May 208.6 12 June 146.2 10 July 211.3 15 August 157.9 18 September 210.3 11 October 140.2 13 November 36.3 3 December 7.4 1 Total 1435.9 101 Source: Yearly bulletin of Meteorological Information, National Horticultural Research Institute (NIHORT, 1999). Table 2: Characteristics of grain amaranth varieties used in the study. Variables NH84/445 NH84/452 NH84/493 Leaf color Purple Green Green/Purple Stem color Green Green Green Base Seed color White Pale Yellow Pale Yellow Days to 50% flowering 54 56 61 Disease tolerance to Choanephora cucurbitarum Low Medium High Mean

grain yield (g/plant) 10.7 13.5 26.0 Table 3: Pre-cropping chemical and physical soil characteristics of the experimental site in

1999. Early Late Properties season season pH (H20) 4.9 5.7 Organic carbon (g/kg) 3.3 3.9 Total Nitrogen (g/kg) 0.42 0.49 Available phosphorus (mg/kg) 3.7 4.3 Exchangeable Fe (cmol/kg) 0.40 0.31 Exchangeable Ca (cmol/kg) 0.8 2.2 Exchangeable Mg (cmol/kg) 0.68 0.50 Exchangeable K (cmol/kg) 0.25 0.20 Exchangeable Mn (cmol/kg) 0.14 0.15 Exchangeable Al (cmol/kg) 0.09 0.05 Exchangeable Na (cmol/kg) 0.30 0.30 Total acidity 0.35 0.36 CEC (cmol/kg) 2.38 3.56 Sand (g/kg) 890.0 870.9 Silt (g/kg) 20.0 20.4 Clay (g/kg) 90.0 90.7

Table 4: Influence of P rates and varieties on amaranth grain yield (kg/ha) in 1999 at Ibadan. Season ____________________ Early Late Mean

P rates (kg/ha) 0 484.0 822.4 653.2 30 774.4 1,076.8 925.6 60 759.2 992.0 875.6 90 641.6 861.6 751.6 SE+ 50.6 53.3 30.1 LSD (5%) 103.2 114.6 60.4

Variety: NH84/452 559.5 807.5 683.5 NH84/445 650.0 912.6 781.3 NH84/493 785.0 1094.5 939.8

SE+ 32.0 46.5 40.7 LSD (5%) 82.0 93.6 92.8

Interaction* SE+ PxS = 20.2 VxS = 40.7 VxP = 35.8 SxPxV = 17.2 LSD (5%) PxS = 49.5 VxS = 92.8 VxP = 78.1 SxPxV = 35.3

*P = Phosphorus, S = Season, V = Variety. Table 5: Influence of P rate on P accumulation parameters averaged across varieties in 1999.

P rates ---------------------------- P Uptake (mg/plant x 10-3) -------------------------------- ---------------P Uptake (mg/plant x 10-3 ------------- (kg/ha) Leaf Stem Root Grain Total Leaf Stem Root Grain Total -------------------------- 1st Cropping -------------------------------- ---------------------------- 2nd Cropping ------------------------------

4 WAP (Weeks After Planting) 0 4.16 0.59 0.19 - 4.94 5.44 1.08 0.40 - 6.92 30 48.67 1.73 0.60 - 51.00 57.26 3.05 0.98 - 61.29 60 59.61 1.93 0.72 - 62.26 63.36 3.80 1.05 - 68.21 90 55.73 1.55 0.51 - 57.79 60.13 2.60 0.82 - 63.55 LSD (5%) 33.86 NS NS - 36.4 22.18 NS NS - 2.18

50% Anthesis 0 25.78 93.79 5.0 - 125.0 31.0 118.0 15.0 - 164.0 30 162.72 416.00 23.0 - 602.0 122.0 310.0 45.0 - 477.0 60 182.21 482.00 26.0 - 690.0 191.0 546.0 53.0 - 790.0 90 156.06 353.00 21.0 - 530.0 167.0 390.0 45.0 - 602.0 LSD (5%) 42.30 20.12 2.6 - 203.0 21.0 107.0 22.0 - 218.0

15 WAP (Weeks After Planting) 0 36.0 133.0 9.0 17.0 195.0 69.0 293.0 31.0 52.0 445.0 30 139.0 336.0 34.0 80.0 589.0 247.0 840.0 75.0 140.0 1302.0 60 211.0 618.0 33.0 104.0 966.0 295.0 854.0 91.0 160.0 1400.0

90 194.0 463.0 21.0 81.0 759.0 251.0 703.0 81.0 123.0 1158.0 LSD (5%) 20.93 114.0 8.6 29.0 249.0 107.0 328.0 11.0 25.7 593.0 Table 6: Influence of varieties on P accumulation parameters averaged across P rates in 1999. ------------------------------ P Uptake ------------------------------- -------------------------------P Uptake --------------------------------- Variety Leaf Stem Root Grain Total Leaf Stem Root Grain Total ------------------ 1st Cropping (mg/plant x 10-3) ------------------ ------------------- 2nd Cropping (mg/plant x 10-3 -------------------

4 WAP (Weeks After Planting) 452 21.18 0.85 0.30 - 22.33 23.04 1.38 0.46 - 24.88 445 15.43 0.58 0.21 - 16.22 17.48 1.06 0.28 - 18.82 493 10.78 0.47 0.18 - 11.43 11.56 0.76 0.26 - 12.58 LSD (5%) NS NS NS - NS NS NS NS - NS

50% Anthesis 452 55.0 149.0 11.0 - 215.00 86.0 232.0 19.0 - 337.0 445 47.0 128.0 9.0 - 184.00 57.0 175.0 17.0 - 249.0 493 42.0 107.0 5.0 - 154.00 28.0 115.0 15.0 - 157.0

LSD (5%) NS 18.0 NS - 73.00 NS 22.0 NS - 39.0

15 WAP (Weeks After Planting) 452 78.0 260.0 15.0 9.17 362.00 106.0 301.0 28.0 24.0 459.0 445 49.0 198.0 15.0 11.05 273.00 70.0 240.0 26.0 26.0 362.0 493 43.0 112.0 9.0 2.85 167.00 55.0 167.0 18.0 20.0 260.0 LSD (5%) 8.0 30.0 3.0 36.0 31.0 21.0 30.0 3.0 NS 45.0 Table 7: Influence of P rate on P accumulation parameters and components of P efficiency averaged across varieties at 15 WAP in 1999. P rate P rate (kg/ha) (g/plant) Gw/Ps Pt/Ps Gw/Pt Pg/Pt Gw/Pg Gw/Ps Pt/Ps Gw/Pt Pg/Pt Gw/Pg --------------------------------- Early Cropping --------------------- ---------------------- Late Cropping --------------------- 0 0.0 - - 31.03 0.09 355.9 - - 23.11 30 0.38 25.47 1.55 16.40 0.01 75.6 35.42 3.43 10.33 60 0.75 12.65 1.29 9.80 0.11 58.2 16.53 1.87 8.85 90 1.13 7.10 0.67 10.60 0.11 77.7 9.53 1.03 9.30 LSD (P=0.05) 4.39 0.05 13.00 NS 182.0 6.26 0.24 Ps = P supplied (g/plant); Gw = Grain yield (g/plant); Pt = Total P uptake; Pg = P uptake in grains; Gw/Ps = P-use efficiency; Pt/Ps = P uptake efficiency; Gw/Pt = P utilization efficiency; Pg/Pt = P harvest index; Gw/Pg = Grain produced per unit of gram P.

Table 8: Influence of amaranth variety on P efficiency parameters and components of P efficiency averaged across P rates in 1999. Variety Gw/Ps Pt/Ps Gw/Pt Ps/Pt Gw/Pg Gw/Ps Pt/Ps Gw/Pt Pg/Pt Gw/Pg -------------------------- 1st Cropping -------------------------------- ---------------------------- 2nd Cropping ------------------------------ NH84/452 10.65 0.64 16.77 0.0253 661.9 16.19 0.81 21.0 0.0522 384.5 NH84/445 14.58 0.48 30.40 0.0405 752.0 20.88 0.64 32.8 0.0718 457.7 NH84/493 18.53 0.29 63.20 0.0171 3705.2 26.05 0.46 57.1 0.0769 742.5 LSD (P=0.05) 1.14 0.04 5.01 NS 70.3 2.93 NS 7.6 NS 62.0 Ps = P supplied (0.57g/plant); Gw = Grain yield (g/plant); Pt = Total P uptake; Pg = P uptake in grains; Gw/Ps = P-use efficiency; Pt/Ps = P uptake efficiency; Gw/Pt = P utilization efficiency; Pg/Pt = P harvest index; Gw/Pg = Grain produced per unit of grain P. Fig. 1: Exel ( Effect of p rates in amaranth grain yields)