Soybeans [Glycine max (L.) Merr.] have not responded favorably to no‐till culture on some Mississippi soils. Positional unavailability of surface‐applied fertilizers may be one reason for the poor response. A 2 X 2 X 3 factorial field experiment with five replications in a randomized complete block split‐split plot design was used to measure effects of tillage (conventional vs. no‐tillage), P and K placement (broadcast vs. injected), and P and K rates (0 and 0, 13 and 37, 40 and 112 lb/acre P and K, respectively) on soybean growth and yield from 1983 to 1985 on three soils. The soils were Okolona silty clay (fine, mont‐morillonitic, thermic Typic Chromudert) at Brooksville, Memphis silt loam (fine‐silty, siliceous, thermic Typic Hapludalf) at Raymond, and Prentiss very fine sandy loam (coarse‐loamy, siliceous, thermic Glossic Fragiudult) at Newton. All soils were initially low in P and K. Seed yields in general were lowest at Brooksville, and ranged from 16.4 to 22.4 bu/acre with a 3‐yr average of 19.4 bu/acre. Yields were much better at the two other sites, except Raymond in 1983 when seed yield averaged 16.9 bu/acre. The Raymond site had the best overall average yield of 29.2 bu/acre, while the 2‐yr average at Newton was 28.2 bu/acre. No‐tillage reduced growth and yields on the Okolona and Memphis soils. On the Prentiss soil, only growth was reduced by no‐tillage. Under no‐till conditions,injection of P and K produced greater yields than broadcast on the Okolona and Memphis soils but not on the Prentiss soil. There was little response to rate of P and K rates on either soil. The low yields on Okolona silty clay appeared to be related to variables not considered in this study.

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Two experimental soybean [Glycine max (L.) Merr.] lines that had produced nearly similar seed yields when grown at Stoneville, MS, differed widely when grown at Newton, MS. This study was conducted to identify the cause for the low seed yield of one line at Newton. Previous studies at this location on soils limed to a pH of 7.0 had shown that ‘Forrest’ soybean increased in yield when fertilized with zinc. Data are not available to show that soybean genotypes differ in efficiency of Zn absorption, so studies were initiated to determine whether Zn concentration in the foliage was different between the two experimental soybean lines. Fully developed trifoliolate leaves were taken from the upper part of the plant at the R1 growth stage and analyzed for concentration of Zn. The low‐yielding line D82‐3298 contained 18 to 25 μg g‐1 of Zn, while D77‐6056, the high yielding line, had 48 to 56 μg g‐1 of Zn. These results indicated that the two did differ in efficiency of Zn absorption. Three hundred thirty F3 lines from the cross D77‐6056 × D82‐3298 were grown along with parents in the same area the following year. The mean Zn concentration for the parental lines was 18.8 ±; 1 μg‐lfor D82‐3298 and 36.9 ± 2.6 μg g‐1 for D77‐6056. The distribution of F3 lines for Zn concentration suggests that only a few genes control Zn absorption efficiency or inefficiency. In additional plantings, D82‐3298, D77‐6056, and Forrest were grown with and without Zn fertilization. D82‐3298 gave a significant (P < 0.05) increase in foliar Zn concentration and seed yield when fertilized with ZnSO4 at Newton, but not at Stoneville. D77‐6056 and Forrest gave no response at either location.

It is reasonably well accepted that the standard procedures developed for isotropic homogeneous metals using linear elastic fracture mechanics models are not appropriate for either continuously or discontinuously reinforced metal matrix composites. For example, the ASTM plane strain fracture toughness test methods typically give widely different values of fracture toughness depending on the particular test specimen geometry as well as the fiber orientation. For unidirectional boron/aluminum composites one finds approximately a factor of two difference between the measured values of fracture toughness obtained from a center-notched test coupon and that given by a compact tension specimen. In particular for unidirectional composites, and to a slightly lesser degree for angle ply laminates, the dominant controlling mechanism for this behavior is matrix plasticity. A secondary toughening mechanism, resulting from the matrix plasticity, is stable transverse fiber failure. The present paper will focus on both the influence of the large plastic zone at the end of the notch and on the constraint that the fibers impose on the shape of this zone, as well as the transverse crack growth. First, a review of some particular experimental studies and methods of analysis for predicting crack growth and fracture of notched unidirectional metal matrix composites is given. Next, two mechanistic models for unidirectional composites with damage are presented. The first is an improved shear lag model that accounts for both of the above damage modes, and the second describes a recent extension of the shear lag concept in an attempt to include transverse stresses. A related finite width laminate model is then discussed, and it is indicated that an isotropic finite width correction factor is reasonably accurate for most center-notched test coupons.