Some factors affecting germination and emergence of sub‐tropical pasture legumes in Rhodesia

Abstract

The effect of depth of seeding, moisture stress, shading and mulching on the emergency of a number of sub‐tropical pasture legumes was examined on two contrasting soil types in the greenhouse.

The legume species used were Desmodium intortum, D. uncinatum, Glycine wightii, Macroptilium atropurpureum, Stylosanthes guianensis and Trifolium semipilosum.

Two contrasting soils were used, a granite‐derived sand and a silt‐rich soil which forms a crust.

Surface seeding was unsatisfactory on both soil types and the highest rate of emergence of all species was obtained with sowing depths of 5 or 10 mm. However, several of the legumes, including some with relatively small seeds, were tolerant of deeper sowing on the sandy soil.

Differential moisture stress was induced by varying the amount and frequency of water application. These treatments were applied in combination with various shading and mulching treatments. Under conditions of moisture stress both shading and mulching incrsased seedling emergence. On the silt‐rich soil where moisture was adequate, shade was beneficial but mulching was harmful.

On the silty soil, seedling emergence was correlated with the strength of the crust. Crust strength was found to vary with time as the soil dried out, increasing initially but subsequently decreasing. Certain discontinuities in the pattern of water loss during drying were found in the silt‐rich soil. These seem to be associated with cracking of the soil surface. This aspect warrants further investigation as does the apparently harmful effect of the mulch under conditions of adequate moisture.

Uittreksel

Die invloed van ‘n aantal faktore (diepte van plant, skaduwee, vogspanning, ‘n grondkombers (dek‐laag) en twee verskillende grondsoorte) op saailingopkoms by ses weidingpeulgewasse is in ‘n glashuis ondenoek.

Die betrokke peulgewasse is die volgende: Desmodium intortum, D. uncinatum, Glycine wightii, Macroptilium atropurpureum, Stylosanthes guianensis en Trifolium semipilosum.

Die twee uiteenlopende grondsoorte wat gebruik is, is onderskeidelik ‘n sand van granietiese oor‐sprong en ‘n slikryke grond wat sterk toeslaan en ‘n oppervlaktekors vorm.

Oppervlakte‐plant was by albei grondsoorte onbevredigend; die hoogste mate van saailingopkoms is deurgaans met plantdieptes van 5 of 10 mm verkry. Verskeie van die peulgewasse net egter met dieper plantdieptes in die sand betreklik goeie opkoms vertoon, ondanks hulle fyn sade.

Differensiële grondvogspanning is teweeggebring deur die hoeveelheid en frekwensie van water‐toediening doelmatig te varieer. Sodanige vogbehandelings is gekombineer met skadu‐ en grond‐kombersbehandelings. Onder toestande van vogtekort het sowel skaduwee as die grondkombers saailingopkoms bevorder. Met voldoende vog in die slikgrond was skadu bevorderlik vir saailingopkoms maar die grondkombers was egter nadelig.

By die slikgrond kon saailingopkoms met die sterkte van die oppervlaktekors gekorrelleer word en met die uitdroging van die grond het die kors aanvanklik geleidelik sterker geword, om weer met verdere uitdroging minder sterk te word. Verskeie onderbrekings in die patroon van waterverlies is by die slikgrond waargeneem; dit blyk gekorrelleer te wees met die vorming van oppervlaktebarste tydens uitdroging. Hierdie verskynsel blyk verder aandag te regverdig, asook die oënskynlike skadelike uit‐werking van die grondkombers onder toestande van voldoende grondvog.