Risk and crop production intensification options for semi-arid southern Zimbabwe

Esther Nyaradzo Masvaya

Research output: Thesisinternal PhD, WU


Although rainfed cropping in semi-arid areas is risky due to frequent droughts and dry spells, climate smart agriculture (CSA) and sustainable intensification (SI) technologies have a role to play in ensuring smallholder farmers in semi-arid sub-Saharan Africa (SSA) are food self-sufficient. Conservation agriculture (CA) and cereal-legume intercropping were identified as cropping systems that have potential to produce food in risky environments. The objective of this study was to determine the potential of CA and intercropping to contribute to SI and CSA by quantifying crop productivity and soil N dynamics using field and modelling approaches.

An on-farm field experiment was set up in Matobo where the effects of two principles of CA (reduced tillage and mulch application) in combination with soil fertility amendments on soil mineral N release, plant N uptake and maize yields were assessed in comparison with the plough tillage. Ploughing stimulated N mineralisation and maize N uptake more than the ripper tillage. However, mulching reduced mineralisation and subsequently lowered crop N uptake compared with no mulch application under the plough tillage. Ripping combined with mulch application resulted in mineral N values and maize yields comparable to the plough only treatment. Planting early (1 Nov to 15 Nov) and with the first rains, especially with the ripper + mulch treatment, resulted in exceeding the food self-sufficiency threshold of 1080 kg ha-1 if fertility amendments were applied, as well as in a low probability of complete crop failure, ranging from 0–40%.  The field experiment was complimented with a modelling exercise using APSIM to investigate the effects of different planting date, tillage and soil fertility management strategies on crop yields over a larger range of climate and risk related issues. APSIM simulated the occurrence of the mineral N flush with the first rains. Its coincidence with planting resulted in average yield benefits in the range of 200-800 kg ha-1.

Maize-cowpea intercropping experiments were established covering several seasons to determine effects on soil chemical variables, root dynamics and yield of intercrops. With the addition of 40 kg N ha−1, maize grain yields were increased significantly by 500–1100 kg ha−1 in a normal season. However, cowpea yields were compromised attributed to the lack of below-ground niche differentiation in root distribution between maize and cowpea. Most intercrops had a land equivalent ratio >1 showing that there was generally greater productivity and over-yielding in the intercrops proving intercropping a robust option across seasons and soil types.

Modelling the maize-cowpea intercrop with APSIM showed that maize yields were reduced by 3–25% with intecropping in comparison with sole maize. For cowpea, a week’s delay in planting resulted in significant reductions in yields. Planting maize and cowpea at populations of 37 000 and 74 000 plants ha-1 respectively on the same date and with 40 kg N ha-1 scenario maximised the probability of meeting household energy and protein requirements on sandy soils. On the clay, the relay intercropping scenarios where cowpea was planted 2–4 weeks after maize met household nutrition needs. Maize-cowpea intercropping was better than growing sole crops as it is a more efficient system to achieving food security in smallholder farms.

The CA and intercropping technologies proved climate-smart to some extent by improving productivity under an uncertain climate. Other than productivity, both CA and intercropping were shown to contribute significantly towards soil fertility environmental sustainability and food self-sufficiency and therefore sustainable intensification. These technologies will need to be accompanied by the application of N containing fertility amendments as these proved critical to reducing the risk of crop failure and achieving the best possible yields.

Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • Wageningen University
  • Giller, Ken, Promotor
  • Descheemaeker, Katrien, Co-promotor
  • Nyamangara, J., Co-promotor, External person
Award date27 May 2019
Place of PublicationWageningen
Print ISBNs9789463434379
Publication statusPublished - 27 May 2019


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