Elsevier

Soil and Tillage Research

Volume 168, May 2017, Pages 125-132
Soil and Tillage Research

Tillage, mulch and fertiliser impacts on soil nitrogen availability and maize production in semi-arid Zimbabwe

https://doi.org/10.1016/j.still.2016.12.007Get rights and content

Highlights

  • Plough tillage stimulated N mineralisation more than ripper tillage.

  • Maize N uptake under the ripper tillage was 13–23% less than with plough tillage.

  • Mulch incorporation with ploughing decreased N mineralisation and crop N uptake.

  • Adding N in fertiliser and manure increased maize yields and is key for production.

Abstract

Conservation agriculture has been promoted widely in sub-Saharan African to cushion smallholder farmers against the adverse effects of soil fertility decline, stabilize crop yields and increase resilience to climate change and variability. Our study aimed to determine if aspects of CA, namely tillage and mulching with manure and fertiliser application, improved soil mineral N release, plant N uptake and maize yields in cropping systems on poor soils in semi-arid Matobo, Zimbabwe. The experiment, run for three seasons (2012/13–2014/15), was a split-split plot design with three replicates. Tillage (animal-drawn ploughing and ripping) was the main plot treatment and residue application was the sub plot treatment with two levels (100% residues removed or retained after harvest). Five fertility amendments (mineral fertiliser at 0, 20 and 40 kg N ha-1, 5 t ha-1 manure only and 5 t ha-1 manure + 20 kg N ha-1) were sub-sub plot treatments. Plough tillage stimulated N mineralisation by 4–19 kg N ha-1 and maize N uptake 13–23% more than the ripper tillage. When mulch was added to the plough tillage, mineralisation was slowed resulting in less crop N uptake (by 5–19%) compared with no mulch application. N uptake was highest in the manure treatments. N recovery and agronomic N efficiency by maize were highly variable over the three seasons, reflecting the uncertainty complicating farmers’ decision making. Nitrogen recovery in the manure treatments was generally poor in the first season resulting in low grain yields in the range 100–260 kg ha-1 regardless of tillage, though higher in subsequent seasons. In the second season manure application gave the largest grain yields under the ripper tillage, both with and without mulch averaging 1850 and 2228 kg ha-1 respectively. Under the plough tillage, the 40 kg N ha-1 treatment gave the highest grain yields of 1985 kg ha-1. In the third season yields were generally poor under all treatments due to low and poorly-distributed rainfall. The CA principles of minimum soil disturbance and maintenance of a permanent mulch cover resulted in reduced soil mineral N availability for crop uptake and poor maize yields. Nutrient inputs through mineral fertilisers and manure are key to ensuring production in such infertile, sandy soils which predominate in semi-arid regions of southern Africa.

Introduction

Smallholder farmers practicing rainfed agriculture in sub-Saharan Africa (SSA) face a myriad of challenges; these include poor soil fertility, low incomes, labour and land constraints, and are further exacerbated by climate variability (Mupangwa et al., 2012, Ngoma et al., 2015, Rurinda et al., 2013). Different approaches to improve soil fertility have been proposed including biological nitrogen fixation, soil surface residue management, fertiliser use, enhanced recycling of animal manure and conservation agriculture (Hobbs, 2007, Mupangwa et al., 2012, Ncube et al., 2009, Nyamangara et al., 2005).

Conservation agriculture (CA) has been promoted throughout sub-humid and semi-arid areas of SSA to cushion smallholder farmers against the adverse effects of soil fertility decline, crop yield decline, and climate change and variability (Hobbs et al., 2008, Ngoma et al., 2015). CA is based on three principles: (i) minimum or no tillage to minimise soil disturbance, (ii) diversification of crop species (often with legumes) grown in rotation and/or association, and (iii) maintaining semi-permanent or permanent soil cover, for example by leaving at least 30% of crop residues (FAO, 2011, Stevenson et al., 2014). This three-pronged approach is reported to have the potential to improve farm resource use efficiency and crop yields especially where moisture is limiting (Hobbs et al., 2008).

Although CA is promoted as a soil-fertility enhancing technology, application of crop residues poor in N, such as cereal stover, may result in prolonged immobilisation of mineral N (Giller et al., 1997). In CA systems, reduced N availability has been attributed to slow residue decomposition and N losses from leaching and denitrification (Angás et al., 2006, Verachtert et al., 2009). Nyamangara et al. (2014) proposed that larger N inputs may be required under CA to offset the N immobilisation caused by cereal stover. A combination of high quality manure combined with low quality crop residue may reduce N leakage and increase nutrient use efficiency (Kihara et al., 2011). Qin et al. (2015) found that larger N inputs resulted in a positive effect of straw mulch on maize yields. In sub-humid west Africa, maize grain yield in a no-till system was only increased by mulch when fertiliser was also applied (Lal, 1995). However, smallholder farmers in SSA typically apply only small amounts of N which may not be adequate. (Vanlauwe et al., 2014) argue that appropriate fertiliser use should be considered a fourth principle of CA as fertiliser is required to enhance both crop productivity and produce sufficient crop residues to ensure soil cover.

In the current smallholder farming system, the perturbation by tillage stimulates a flush of mineral N (the “Birch effect”) with the start of the rains (Chikowo et al., 2004, Giller et al., 2011), whereas soil organic matter may have otherwise been protected from degradation. This “Birch effect” is reported to be short-lived and the decomposition rates may fall back to rates similar to that of an undisturbed soil (Andersson and Giller, 2012). Minimum tillage promoted in smallholder areas in SSA under CA is mainly focused on the hand hoe planting basins (Giller et al., 2011, Nyakudya and Stroosnijder, 2015). Farmers with limited access to draught power and using hand hoes prepare their fields in the dry season in order to spread labour requirements for land preparation, allowing for early planting (Nyamadzawo et al., 2012). However, the use of animal drawn conservation tillage methods such as the ripper and direct seeder provides an opportunity to reduce the labour demand associated with land preparation using hand hoes. Mechanisation can increase productivity per unit area by improving timeliness of farm operations including planting. Early planting may coincide with the “Birch effect” which is beneficial to the crop (Chikowo et al., 2004). Minimum soil disturbance in CA systems, however, results in slower mineralisation compared with conventional tillage because of the minimum disturbance (Chivenge et al., 2007) leading to preservation of soil organic matter from decomposition. Due to this slow mineralisation, (Lal, 2007) suggested that resource poor farmers would be better off ploughing their sandy soils to enhance mineralisation of whatever soil organic matter present to enhance nutrient supply in the short term. There are, however, no detailed studies on seasonal mineral N availability in the semi-arid areas under CA practices such as minimum tillage and crop residue retention particularly on soils of poor fertility that are typical in smallholder agriculture in SSA.

We hypothesise that for cropping systems in semi-arid climates and on poor fertility soils, the benefits of CA and added mulch are in immobilising N so that it is not lost from the system and becomes available later for crop growth. The study specifically aimed at determining if and how tillage, mulching, manure and fertiliser application and their interactions improved soil mineral N release, plant N uptake and ultimately maize yields.

Section snippets

Site description

The study was carried out in Nqindi ward, Matobo district, Matabeleland South, Zimbabwe (20 39.58′S, 28 15.58′ E; 900 masl). Matobo district lies in Agroecological Zone IV, characterised by semi-arid climate typical of south west Zimbabwe. Rainfall is unimodal with a distinct wet (November–March) and dry (April–October) season. The wet season receives 450–650 mm annual rainfall with a long term average annual rainfall of 580 mm. Droughts are frequent as are severe dry spells during the wet season.

Rainfall distribution

Rainfall amount, distribution and intensity were erratic and highly variable across the three seasons (Fig. 1). Severe mid-season dry spells characterised the first (2012/13) and third (2014/15) seasons. The first and third seasons received rainfall totals of 272 and 432 mm that were 54 and 27% lower than the long term average for the site (590 mm) respectively and were also below the lower limit (450 mm per annum) for the agro-ecological region. Both seasons were classified as droughts and the

N mineralisation patterns, uptake and recovery

In general, the Conservation Agriculture principles of minimum soil disturbance and maintenance of a permanent soil cover (mulch) resulted in reduced soil mineral N availability for crop uptake and ultimately low yields from a poor fertility soil in semi-arid Zimbabwe. Ploughing enhances the mineralisation of organic matter in the soil by exposing previously unexposed soil surfaces to attack by microbes and by providing the latter with new sources of energy (Peigné et al., 2007). Compared with

Conclusions

We observed that mineralisation, N uptake and crop yields were stimulated under plough tillage compared with the ripper tillage. When mulch was added together with plough tillage, the mineralisation of N, crop N uptake and maize yields were decreased compared with no mulch application under the same tillage. When combined together, following two principles of CA, the ripper tillage and mulch application did not reduce mineralisation and resulted in yields comparable to those obtained under the

Acknowledgements

We thank the Netherlands Organization for International Cooperation in Higher Education (NUFFIC) for funding.

References (50)

  • H. Ngoma et al.

    Does minimum tillage with planting basins or ripping raise maize yields? Meso-panel data evidence from Zambia

    Agric. Ecosyst. Environ.

    (2015)
  • I.W. Nyakudya et al.

    Conservation tillage of rainfed maize in semi-arid Zimbabwe: a review

    Soil Tillage Res.

    (2015)
  • C.A. Palm et al.

    Organic inputs for soil fertility management in tropical agroecosystems: application of an organic resource database

    Agric. Ecosyst. Enviro.

    (2001)
  • R.J. Raison et al.

    Methodology for studying fluxes of soil mineral-N in situ

    Soil Biol. Biochem.

    (1987)
  • W.D. Sakala et al.

    Interactions between residues of maize and pigeonpea and mineral N fertilizers during decomposition and N mineralization

    Soil Biol. Biochem.

    (2000)
  • J.R. Stevenson et al.

    Evaluating conservation agriculture for small-scale farmers in Sub-Saharan Africa and South Asia

    Agric. Ecosyst. Environ.

    (2014)
  • C. Thierfelder et al.

    Conservation agriculture in eastern and southern provinces of Zambia: long-term effects on soil quality and maize productivity

    Soil Tillage Res.

    (2013)
  • B. Vanlauwe et al.

    A fourth principle is required to define Conservation Agriculture in sub-Saharan Africa: the appropriate use of fertilizer to enhance crop productivity

    Field Crop Res.

    (2014)
  • J.M. Anderson et al.

    Tropical Soil Biology and Fertility: A Handbook of Methods

    (1993)
  • J.M. Bremner et al.

    Nitrogen—Total. Methods of Soil Analysis. Part 2. Chemical and Microbiological Properties

    (1982)
  • J. Chianu et al.

    Mineral fertilizers in the farming systems of sub-Saharan Africa. A review

    Agron. Sustain. Dev.

    (2012)
  • R. Chikowo et al.

    Nitrate-N dynamics following improved fallows and maize root development in a Zimbabwean sandy clay loam

    Agrofor. Syst.

    (2003)
  • FAO

    Save and Grow: A Policymaker’s Guide to the Sustainable Intensification of Smallholder Crop Production

    (2011)
  • K.E. Giller et al.

    Building soil nitrogen capital in Africa

    Repl. Soil Fertil. Afr.

    (1997)
  • A.E. Hartemink et al.

    Land cover, extent, and properties of Arenosols in Southern Africa

    Arid Land Res. Manage.

    (2008)
  • Cited by (48)

    • Harnessing the power of cellulolytic nitrogen-fixing bacteria for biovalorization of lignocellulosic biomass

      2022, Industrial Crops and Products
      Citation Excerpt :

      For instance, Anderson (1993) found that returning residues of wheat, corn, millet (Pennisetum glaucum L.), safflower (Carthamus tinctorius L.), and sorghum reduced the growth of goat grass (Aegilops cylindrical host) by 70–85 % and the growth of wheat was reduced 50–70% by the same five crop residues. The most commonly used practice to increase soil nitrogen availability and crop production is the addition of nitrogenous chemical fertilizers to the soil amended with crop residues (Dossou-yovo et al., 2016; Masvaya et al., 2017; Nafi et al., 2020). However, the application of synthetic nitrogen fertilizers can cause environmental pollution as well as alter the global cycle of nitrogen through nitrogen leaching, volatilization, and denitrification (Vitousek et al., 1997).

    • The effect of minimum tillage and animal manure on maize yields and soil organic carbon in sub-Saharan Africa: A meta-analysis

      2021, Environmental Challenges
      Citation Excerpt :

      Conventional tillage usually out yields minimum tillage due to N mineralization's speeding up from soil organic matter due to soil disturbance and microbial degradation of exposed protected organic matter due to soil structure disruption (Balesdent et al., 2000). For example, in Zimbabwe, Masvaya et al. (2017), comparing minimum tillage with conventional tillage, there was a depressed maize grain yield by 4–60% when minimum tillage was used. A study in Nepal by Balesdent et al. (2000), after two years, showed conventional tillage yielded more maize yields than minimum tillage.

    View all citing articles on Scopus
    View full text