Boron deficiency in fresh-market tomatoes (Lycopersicon esculentum Mill.) is a widespread problem that reduces yield and fruit quality but is often not recognized by growers. Tomatoes were grown in field and hydroponic culture to compare the effects of foliar and soil applied B on plant growth, fruit yield, fruit quality, and tissue nutrient levels. Regardless of application method, B was associated with increased tomato growth and the concentration of K, Ca, and B in plant tissue. Boron application was associated with increased N uptake by tomato in field culture, but not under hydroponic culture. In field culture, foliar and/or soil applied B similarly increased fresh-market tomato plant and root dry weight, uptake, and tissue concentrations of N, Ca, K, and B, and improved fruit set, total yields, marketable yields, fruit shelf life, and fruit firmness. The similar growth and yield responses of tomato to foliar and root B application suggests that B is translocated in the phloem in tomatoes. Fruit from plants receiving foliar or root applied B contained more B, and K than fruit from plants not receiving B, indicating that B was translocated from leaves to fruit and is an important factor in the management of K nutrition in tomato.

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Computer simulation models of crop-soil systems offer the potential to increase understanding of soil N cycle processes, thereby improving management of N resources in agricultural systems. NCSWAP (Ni· trogen, Carbon, Soil, Water, And Plant) is a comprehensive, deterministic computer model of the plant-soil system that simulates seasonal soil C and N cycles under the control of temperature, moisture, mi· crobial activity, and crop growth. The objective of this study was to validate NCSWAP using data collected during a 3-yr N-rate study in central Pennsylvania that investigated seasonal N dynamics in com (Zea mays L.) provided with N as liquid dairy manure or as NH 4 N0 3 • Seasonal soil N0 3 concentration in the upper soil layer, seasonal aboveground N accumulation by com, and water leached past 1.2 m during the second year of the study were used to calibrate input values con· trolling soil water flow and N0 3 production from mineralization of soil organic N sources. The validation of NCSWAP identified several limitations in the water flow and C and N cycling submodels as well as in the potential of the model to simulate seasonal N dynamics in corn. Validation simulations were about as accurate as calibration simulations, reflecting the ability of the model to simulate C and N dynamics without recalibration from year to year. Much of the sim· ulation error was related to an overestimation of N0 3 leaching caused by the inability of the model's microporous flow submodel to simulate the macropore·influenced water flow in the well-structured soil used in the validation.M UCH ATTENTION has been focused on N fertilizer management because of its importance to agricultural production and its potential for environmental impact (Keeney, 1982). The availability of N to crops is controlled by the interplay between environmental factors, such as temperature and precipitation, and the multitude of biological and chemical transformations that make up the N cycle.The complex nature of the soil N cycle has frustrated efforts at more carefully managing N resources in agricultural systems. The inability to coherently grasp the numerous physical, chemical, and biological processes that regulate the N cycle has limited the development of more efficient N management strategies. Developments in computer technology and the refinement of systems modeling offer a method of integration and synthesis of large and complex bodies

This article reconciles two notions of soil-quality indexes with the economic concepts of technical efficiency and productivity growth. An example uses data from the U.S. Department of Agriculture's experimental fields in Maryland and data envelopment analysis techniques to estimate a soil-quality index consistent with the notion of technical efficiency. Common regression techniques shed additional light on the role of individual soil-quality properties in a very restricted linear approximation of the estimated soil-quality index. Copyright 1999, Oxford University Press.