By Tonny Tauro, Grace Kanonge-Mafaune, Hatirarami Nezomba, Esther Masvaya, and Justice Nyamangara
Microbial phosphorus (P) immobilization is a hidden challenge in most parts of sub-Saharan Africa. It affects crop establishment, growth, and response to mineral nitrogen (N) fertilizer application that ultimately reduces crop yields. This research highlighted that split application of N in combination with a medium rate (7 t ha-1) cattle manure and P fertilizer (>36 kg P ha-1) (an intensification pathway) reduced microbial immobilization and increased P uptake subsequently increasing root biomass productivity.
To achieve the second goal (zero hunger) of United Nations Sustainable Development Report, the first goal of the African Union 2063 Agenda on “The Africa We Want”, and the “2030 Vision of Zimbabwe” for agriculture to drive economic growth in Zimbabwe (African Union, 2015; United Nations, 2010; Government of Zimbabwe, 2021), there is need to build soil available P. Food insecurity is fueled by the low crop yields partly linked to low soil available P. Maize yields have remained low (< 1 t ha-1) because smallholder farmers are cropping on the predominantly sandy soils, which have severe fertility constraints particularly linked to the low soil available P (Mapfumo and Giller, 2001; Mashingaidze et al., 2009). Most of these sandy soils are granite derived and subsequently characterized by low P stocks, soil acidity, low organic matter and low N (Soropa et al., 2019; Mtali-Chafadza et al., 2020).
Phosphorus is the first limiting nutrient in acidic tropical soils of Africa such as under Andosols, Ferralsols, and Acrisols covering about 37%, 21%, and 14%, respectively, due to their high P-fixing capacity (Buehler et al., 2002). Furthermore, most locally available amendments are deprived of P (< 1.5 kg P t-1), that is far short to meet a household bare requirement maize yield (Mapfumo and Giller, 2001) and must be co-applied with P-based fertilizers. Furthermore, the major challenge with P is attributed to the high reactive nature of the phosphate anions, which behave differently under acidic/alkaline conditions (Garg and Bahl, 2008). Given that cereals respond to N fertilizer only when P deficiency has been ameliorated (Nezomba et al., 2009), improving soil available P is essential in unlocking food security in Zimbabwe, an idea that agrees with findings of Nezomba (2016). Recent studies have shown P microbial immobilization and leaching in sandy soils as a major drawback in increasing soil available P in non-fixing soil of Zimbabwe (Tumbure et al., 2022; Tauro et al., 2023). Few studies have assessed the impact of increasing P rate on soil available P and offsetting microbial P immobilization, which is the aim of this research.
Experimental description
A 2 x 6 factorial greenhouse experiment was established at Soil Productivity Research Laboratory (SPRL) in Marondera, Zimbabwe. The first factor being cattle manure rate from kraals with livestock under natural grazing (Table 1), and six mineral P rates being the second factor.
Cattle manure was be applied at 0, 3, and 7 t ha-1 and in combination with: 0, 18, 24, 30, 36, and 42 kg P ha-1. Treatments were arranged in a randomized complete block design and each block had 18 treatments with 100 kg N ha-1 and 35 kg K ha-1 applied to all treatments excluding the control. Potassium (K) was applied as muriate of potash and P was applied as single super phosphate (SSP). Fertilizer N was ammonium nitrate, and the total rate was split applied with the first 20% at planting. The other 30% and 40% of N was applied at 2 and 6 weeks after crop emergence (WAE), respectively. The maize was maintained for 10 WAE with plant height, general observations, shoot and root biomass, and P uptake measured and or noted.
Changes in maize height over time
Maize height significantly increased across all treatments starting at 4 WAE (Fig. 1). Height fluctuated under the control with and without 3 t manure ha-1 (Fig. 1a and b). Without manure, the trajectory of growth was similar across P application rates with the exception of 42 kg P ha-1, which was the flattest (Fig. 1a). Treatments including 3 t manure ha-1 (Fig. 1b) had a similar overall trajectory to corresponding treatments without manure; however, plants receiving 42 kg P ha-1 were highest, while plants receiving 18 kg P ha-1 were slightly shorter. Application of 18 and 24 kg P ha-1 plus 7 t manure ha-1 produced shorter plants compared to treatments with > 30 kg P ha-1 starting at 8 WAE (Fig. 1c).
Maize shoot and root biomass yield
Overall, manure application enhanced the effectiveness of P fertilizer in root biomass, but this was not evident in shoot biomass (Fig. 2). However, no benefit in maize shoot biomass accumulation was evident without P supplementation. Compared to the control, maize shoot biomass significantly increased following addition of 18 kg P ha-1 with or without manure. No difference in shoot biomass was noted under the minus manure treatment regardless of the P rate. A similar incremental trend in maize shoot biomass was noted following the addition of 3 t manure ha-1, but a slight depression was also observed with 36 kg P ha-1. Despite the similarity in maize shoot biomass across treatments with 7 t manure ha-1 plus mineral P, there was a general incremental trend with up to 36 kg P ha-1 and then a decrease with 42 kg P ha-1. The co-efficients of determination were 88%, 69%, and 80% under the minus manure, 3t manure ha-1 and 7 t manure ha-1, respectively.
Like shoot development, without P supplementation, there was no benefit to maize root biomass while addition of 18 kg P ha-1 significantly increased the root biomass (Fig. 2). Consistently across the different P rates, there was no benefit to either 3 or 7 t manure ha-1 to root dry biomass. However, application of 30 and 36 kg P ha-1 produced significantly (P<0.05) more root biomass than the control while at 42 kg P ha-1 it was reduced. Following addition of 3 and 7 t manure ha-1, root biomass significantly (P<0.05) outweighed the control with > 30 kg P ha-1. The co-efficients of determination were 52%, 84%, and 92% under the minus manure, 3t manure ha-1 and 7 t manure ha-1, respectively.
Maize shoot P uptake
Maize uptake was similar from 0 to 30 kg P ha-1 without manure application followed by a significant drop in P uptake at 36 kg P ha-1. The highest uptake was noted following addition of 42 kg P ha-1 (Fig. 3). With 3 t manure, the highest P uptake was at 36 kg P ha-1 followed by a significant drop in P uptake at 42 kg P ha-1. There was no difference in P uptake following application of 7 t manure ha-1 except at 42 kg P ha-1, which was significantly lower than the control.
Summary
Efforts to increase maize growth is dependent on co-application of a high P rate (> 36 kg ha-1) plus organic nutrient resources (7 t ha-1) with split N management. As such farmers may need to intensify productivity by, for example, reducing field sizes to attain > 7 t manure ha-1 and managing their mineral fertilizer use. This research highlights that split application of N in combination with moderate cattle manure application (7 t ha-1) and > 36 kg P ha-1 can improve nutrient availability, enhance plant nutrient uptake, and increase productivity. There is scope for modelling this intensification pathway to see if farmers can achieve household maize self-sufficiency on manageable field sizes.
Acknowledgement
This study was supported by 2022 APNI Young Phosphorus Fellowship Award. I am grateful for mentorship from Ms. Celia Matyanga.
Dr. Tauro (e-mail: phirilani2@yahoo.co.uk) is with the Department of Soil Science and Productivity, Marondera University of Agricultural Sciences & Technology, Marondera, Zimbabwe. Mrs. Kanonge-Mafaune is with the Soil Productivity Research Laboratory (SPRL), Marondera, Zimbabwe. Dr. Nezomba is with the Department of Soil Science & Environment, University of Zimbabwe, Mount Pleasant, Harare, Zimbabwe. Dr. Masvaya and Prof. Nyamangara are with the Climate Change and Food Security Institute, Marondera University of Agricultural Sciences and Technology, Marondera, Zimbabwe.
Cite this article
Tauro, T.P., Kanonge-Mafaune, G., Nezomba, H., Masvaya, E., Nyamangara, J. 2024. The Value of Manure and Phosphorus Application to Unlock Immobilized Microbial Phosphorus for Sustainable Intensification of Maize in Zimbabwe, Growing Africa 3(1), 28-31. https://doi.org/10.55693/ga31.KNGD6756
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