The paper is in two parts. Part I presents results of a Monte Carlo randomization study of Papadakis's covariance method of NN analysis which show that (i) a non-iterated Papadakis analysis tends to be conservatively biassed; (ii) iteration of the analysis as suggested by Bartlett (1978) leads to substantial positive bias in the treatment F ratio; (iii) the method is very inefficient when there are substantial trend effects in the data. A theoretical explanation of these results is given.Part II describes a new method of NN analysis discovered by the first author and developed in collaboration with the co-authors. The method is essentially a "movingblock" analogue of classical forms of analysis for "fixed" blocks (or rows, columns). It avoids the defects of Papadakis's method and leads to approximately unbiassed analyses. It is nearly always and often substantially more efficient on average than classical analyses of complete or incomplete block experiments, and also more efficient than standard analyses of Latin or lattice square designs if there are appreciable row X column interactions in the data. New criteria of design for NN balance are described. Validity of the new method under randomization is demonstrated empirically with Monte Carlo studies.

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The Permanent Rotation Trial at the Waite Agricultural Research Institute in South Australia was established on a red-brown earth in 1925, with predominately cereal-long fallow rotations on 34 adjacent plots. The trial was upgraded in 1948 to include a greater proportion of pasture leys in the rotations and currently contains 11 treatments. The trial is unreplicated; however, each phase of a sequence is represented each year. Seven of the original rotations have remained in an unbroken sequence since 1925: continuous wheat (W), wheat-fallow (WF), wheat-peas (WPe), wheat-pasture-fallow (WPaF), wheatoats- fallow (WOF), wheat-barley-peas (WBPe), wheat-oats-pasture-fallow (WOPaF). For the 11 rotations, soil organic carbon (SOC) in the top 10 cm declined from 2.75% in 1925 to a mean value of 1.56% in 1993. One plot, which had reverted to permanent pasture in 1950, showed the smallest decline with an SOC content of 2.46% in 1993. The greatest declines in SOC were in the 4 original rotations that included fallow phases in the sequence (mean value of 1.22%). In the WF rotation the SOC content had declined from 2.75 to 1.04% during 68 years of cropping. Associated yield decreases showed that the treatment could not sustain production. Soil organic C declined linearly with increasing frequency of fallows and decreasing frequency of pasture in the rotations. Average grain yields (1925-93) in the 7 original sequences ranged from 2.64 t/ha in WOPaF to 0.89 t/ha in the continuous W plot. The linear decline in yields for WBPe, WPaF, WPe, and WOF treatments indicate a convergence in the 1990s under current management, with an average yield of 1.54 t/ha in 1993 and average SOC in the top 10 cm of 1.32%. We hypothesise that the gradual increase in grain yields from the continuous W plot since the 1960s is the result of a gradual build-up of light fraction organic material, which assists in the maintainence of structure and nutrient availability.

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S U M M A R YAxial resistittice (/?") was e.stirtiated from xylem diameter tnieasuretnents obtaitied from periodic acid atid toluiditie blue O (PAS-TBO) staitied sectiotis of Vitis vinifera L. cv. Shiraz. Multiple litiear regressioti showed a strotig negative felationship between axial resistance atid either root diameter or distatice frotn the root tip. Water stress treatmetits did not affect the relationships, but plant age significatitly influenced the ititercept of the legrcssion. The use of both lignin atid cytoplasm stain showed that some vessels retaitied degenerating protoplastn which would impede water flow. Iticlusioti of these vessels iti calculatiotis of axial resistatTce could account for the underestimatioti reported by some authors in cotiiparisoti with experitnental detertninatiotis. Calculations based on the assumptioti that all xyletn vessels, large atid stnall, ate itivoKed iti axial water cotiductioti showed that use of tneati xylem diatneter tnight result in overestitnatitig \'alues by a tnagtiitude of between 1-7 atid 4-4. The use of individual .xylem x'essel diameters gave tnore accurate estitnatioti of axtal resistatice. Sotne adjacetit secotidary xylem and metaxyletn vessels were observed to merge itito sitigle vessels as a result of breakdown of the wall between thetn. Implicatiotis of sueh a developmetital phetiometion are discussed.