Responses of Cowpea Genotypes to Indigenous Rock Phosphate Application

Abstract

Core Ideas Indigenous RP has possibility as an alternative P source of mineral P fertilizer. Seven cowpea genotypes were identified as good responders to RP application. Application amount at 57 mg P kg−1 as RP was optimum amount for cowpea. Micro‐dosing technic was appropriate for applying powdery RP in the fields. Cowpea [Vigna unguiculata (L.) Walp.] plays an important role in the livelihoods of the people of sub‐Saharan Africa, but phosphorus (P) deficiency in soils is a serious problem that contributes to low productivity. This study was conducted to verify the efficiency of indigenous rock phosphate (RP) as a P source to promote this affordable method of soil management to farmers. Pot experiments were conducted to identify good responder genotypes to RP application and its effect in cowpea cultivation using low‐P soil from Fashola village in southwestern Nigeria and Togolese RP (34% P2O5). Shoot dry weight (SDW) at 8 wk after seeding (WAS) was significantly correlated with P uptake (r = 0.817; P < 0.01) and was therefore used as an indicator to select good responder genotypes. Sixteen of the 28 tested genotypes showed a low rate of decrease of SDW at 8 WAS under Togolese RP applications of 171 mg P kg−1 compared with 30 mg P kg−1 (as KH2PO4). Seven of these genotypes (Iron bean, IT87D‐941–1, IT97K‐499–38, DanIla, IT95K‐1543, IT97K‐556–4, and IT90K‐284–2) showed a significantly higher SDW at 8 WAS compared with IT97K‐499–35. In four of the seven good responders, the SDWs at 8 WAS were significantly higher and grain yield tended to be higher with ≥57 mg P kg−1 compared with zero application. Under field conditions, the micro‐dosing technic is recommended for applying RP to avoid loss and to enhance the availability of P for cowpea cultivation.

Effect of phosphorus application on the performance of some cowpea lines

“…The pot experiment commenced in January 2014 in the screen house at IITA‐Ibadan, Nigeria. A split‐plot design with three replications was conducted with 28 cowpea lines as follows: three genotypes for high productivity without or with P application, three for high productivity without P and low productivity with P, one for high N fixation and P absorption, seven for drought tolerance, two for insect tolerance, three for good performance in Niger Republic, three for Striga tolerance, six that were dual purpose, and two wild relatives of cowpea (Suzuki et al., 2018).…”

“…The soil used for the pot experiment was collected from Fashola village in Oyo State, southwestern Nigeria (07°53′ N, 003°45′ E) and is classified as Oxic Paleustalf (Kolawole et al., 2000); P content (∼1.06 mg kg −1 ), total N (∼0.07 mg kg −1 ) and organic C (∼0.80 mg kg −1 ) are extremely low (Suzuki et al., 2018). The pH and effective cation exchangeable capacity are not low at ∼6.9 (determined by 1:1 water/soil; ∼3.23 cmol c kg −1 ) (Suzuki et al., 2018). Collected soil was air‐dried and sieved with a 2‐mm sieve, and 4.5 kg was placed in each pot; P was applied at the rates of 0 and 30 mg P kg −1 as KH 2 PO 4 .…”

“…(2018) showed that there were high and significant correlations between P uptake and shoot dry weight (SDW) ( r = .817; p < .01) at 8 wk after sowing (WAS). Phosphorus uptake had significant correlation with nodule number ( r = .548; p < .01) but not with nodule and root dry weights (Suzuki et al., 2018). These observations imply that P uptake affects shoots more strongly than roots.…”

Diversified Approaches to Evaluate Wide Genetic Resources of Cowpea for Enhancing New Variety Development for West Africa and Its Social Implementation by Cowpea Research Program of IITA

“…However, in rural areas of Africa, the prices of chemical fertilisers are usually twice the international prices due mainly to transportation costs (Bumb & Baanante, 1996). Suzuki (IITA HQ, 2013-2015, IITA South Africa hub, 2016 evaluated the efficiency of indigenous rock phosphate (RP) as a natural source of phosphate (Suzuki et al 2018). While a single new component such as drought or pest resistance may not be effective by itself, specific combinations of the above can work synergistically.…”

“…Additionally, cowpea fodder is a valuable source of feed for livestock (Singh et al 2003), making it very attractive to small-scale farmers (Kamara et al 2012). As a leguminous crop, cowpea improves soil fertility through its ability to fix atmospheric nitrogen (Sanginga et al 2000) and is tolerant to low soil fertility, including low phosphate levels (Suzuki et al 2018). Collectively, these characteristics have made cowpea a vital component of cropping systems for the dry savannahs of sub-Saharan Africa (SSA) (Table 2; Carsky et al 2001).…”