Changes in the population of germinated seed in a hill pasture during and after a pastoral fallow

Abstract

A pastoral fallow, which involves no defoliation of pasture for a period, generally from spring to autumn, is a management tool that can be used either to reduce plant population density through self-thinning prior to oversowing improved plant germplasm or to encourage natural reseeding in order to increase sward persistence and productivity. Two ®eld experiments were carried out in a hill pasture in New Zealand to quantify the response of the seed population, germinated from soil plugs under glasshouse conditions for over 7 months, to pastoral fallow, as in¯uenced by the timing and duration of the fallow, fertilizer application and aspect, and to identify the germination patterns of different plant species in fallowed and grazed swards. A spring± autumn pastoral fallow increased the germinated seed population of grasses, legumes and weeds by 161%, 51% and 59%, respectively, compared with the grazed control. The variation in germinated seed population during the pastoral fallow showed that seed quantity can be controlled by manipulating the timing and duration of a pastoral fallow. Short duration (2±3 month) pastoral fallows resulted in a signi®cantly lower germinated grass seed population than the full (spring±autumn) fallows. Fertilizer application reduced the germinated grass seed population by 26%. The germinated legume seed population was higher with a shady than a sunny aspect. Regression analysis revealed that the germination patterns of all plant species followed a negative exponential function. Partial differentiation of this function derived a germination rate curve on which a two-pool (ephemeral pool and base pool) model was developed to describe quantitatively the dynamics of germinable seed reserves in the soil.

Impact of deferred grazing and fertilizer on plant population density, ground cover and soil moisture of native pastures in steep hill country of southern Australia

“…, 1996) withheld grazing in at least part of spring and summer to allow reproductive growth and seed production, which may have significantly stimulated tillering of perennial grasses in the following seasons through nutrient translocation (Matthew et al. , 1996) and recruitment of new plants from the seed produced over the deferred grazing period (Nie et al. , 1999).…”

“…, 1998). A 7‐month deferral from grazing resulted in dramatic decreases of 72–87% of the densities of grasses, clovers and other species that were present, but increased the soil seed reserve of the species by 51–161%, creating gaps for seed germination to thicken the sward after deferred grazing (Nie et al. , 1997a, 1999).…”

Impact of deferred grazing and fertilizer on herbage production, soil seed reserve and nutritive value of native pastures in steep hill country of southern Australia

“…During deferred grazing, plant population density such as the tiller density of perennial grasses can be reduced considerably through self‐thinning (Yoda et al ., ; Nie et al ., ). Post‐deferred grazing, tiller density of perennial grasses can be significantly increased due to recruitment of tillers and natural reseeding in autumn and winter (Nie et al ., ; Nie and Zollinger, ). Perennial grasses are essential components of pastures for animal production in temperate regions of Australia (Waters et al ., ).…”

Soil seed-bank germination patterns in natural pastures under different mineral fertilizer treatments

“…[2], a two-pool model was developed to quantitatively describe the dynamics of the germinable seed reserves in the soil, in terms of the transient seeds or ephemeral pool (EP, seeds m -2 ) and persistent seeds or base pool (BP, seeds m -2 ) (Nie et al, 1999). According to Eq.…”