J. P. Millner

The yield and nutritive value of maize hybrids grown for silage

Abstract The effect of hybrid and plant population on yield, metabolisable energy content and nitrogen percentage of forage maize were investigated in a trial which included seven maize (Z. mays L.) hybrids established at 75 000, 100 000, and 140 000 plants/ha. Biomass yield and its distribution among morphological components were measured in all plots, while metabolisable energy content and nitrogen percentage of each component were measured in the 100 000 plants/ha plots only. There were significant hybrid differences in yield and yield distribution among components. Yields ranged from 15 800 to 20 700 kg DM/ha, the greatest contribution coming from grain, followed by stem, cob, and leaf. Plant population had no effect on dry matter partitioning, but forage yields declined significantly at the lowest population. Crop metabolisable energy content ranged from 10.3 to 11.3 MJ/kg DM with significant differences among hybrids, but was not correlated with forage yield or the relative contribution to yield of any component.

Effect of late nitrogen on the yield and quality of spring sown Rongotea' wheat

Abstract Three experiments were conducted at different sites in the Manawatu, New Zealand, to investigate the effects of late nitrogen (N) on the yield and baking quality of ‘Rongotea’ wheat. Four rates of N were applied: 0, 20, 40, and 80 kg N/ha applied at Feekes’ Growth Stage 9. Late N increased grain yield at two sites. Yield responses resulted from an increase in ears/m2 at one site and grain weight at the other. Grain protein % was increased by late N at all sites. Mechanical Dough Development (MDD) bake score, sodium dodecyl sulphate (SDS) sedimentation volume, water absorption, and optimum work input were all positively correlated with grain protein. The regression of SDS sedimentation volume on grain protein % was calculated for each site individually and also with data from all sites pooled. There were differences between the regressions from individual sites and the pooled regression indicating that site influenced the relationship between baking quality and grain protein %.

Stocking Rate and Grazing Season Modify Soil Respiration on the Loess Plateau, China ☆

ABSTRACT The influence of sheep grazing on carbon cycling in the midarid steppe of the Loess Plateau, Gansu, China, was investigated by measuring the CO2 exchange rate in pastures with a 7-year history of zero, light, moderate, and heavy grazing. Farming systems in the area are characterized by heavy grazing pressure and low vegetation productivity. The effect of stocking rate on soil respiration (Rs) was determined using field trials to investigate factors influencing spatial and temporal variation in Rs in August 2008 on two sites: summer grazed and winter grazed. Soil respiration is an important component of the carbon cycle in rangeland. Measurements included daily Rs, soil temperature, soil moisture, and root biomass. Daily Rs was also measured in late April and middle December 2008. The response of Rs to increasing stocking rate in August 2008 differed with site; on the summer-grazed site increased stocking rates reduced Rs (P < 0.02), whereas on the winter-grazed site, stocking rate had little effect on Rs. Path analysis revealed that on the summer-grazed site, soil moisture had the greatest influence on Rs, whereas on the winter site soil temperature was the most important factor; stocking rate had the least influence on Rs at both sites. The results highlight the importance of environmental variability in determining the effects of grazing on Rs.

Seed production trait associations and inheritance in interspecific hybrids between Trifolium repens (white clover) and Trifolium uniflorum

Abstract. Trifolium repens L. (white clover) is an important component of temperate pastures, but its root morphology makes it vulnerable to drought and pest attack. T. uniflorum is a wild species, adapted to dry environments, with deep woody roots but poor vegetative growth and only 1–3 florets per inflorescence (head). Interspecific hybridisation to incorporate the drought tolerance and root characteristics of T. uniflorum into white clover led to primary hybrids (F1 and BC1) with poor seed production. Advanced-generation hybrids expressed high variation for almost all seed-production traits, and seed production responded to selection. To inform future breeding programs, trait associations and heritabilities were analysed. Numbers of heads per plant, florets per head and seeds per floret were important factors with moderate–high heritabilities. The derived traits, numbers of seeds per head, florets per plant and seeds per plant, expressed low–moderate heritabilities. No negative associations between seed production and root traits were found in the hybrids, nor were there any negative associations among head production, persistence and foliage production. Selection for improved seed-production traits should be effective without adversely affecting vegetative traits.