WINTER CROPS AS BIOASSAYS OF SOIL NITROGEN-SUPPLYING CAPACITY

Abstract

Soil nitrogen (N)-supplying capacity bioassays could present alternatives to traditional soil tests. Objectives were to identify winter crops and associated characteristics with bioassay potential. Saint Joseph and Bossier City, LA experiments used randomized complete block designs with factorial N fertilizer and winter crop treatment arrangements. Nitrogen rates were applied to corn (Zea mays L.) in 2004. Unfertilized winter wheat ( Triticum aestivum L.), cereal rye (Secale cereale L.), native winter vegetation, and weed-free winter fallow treatments followed corn. At Saint Joseph, cotton (Gossypium hirsutum L.) followed winter crop treatments. Greater corn N rate consistently increased winter crop biomass and N accumulation, suggesting potential as bioassays, and increased Saint Joseph seedcotton yield. Winter crop-seedcotton yield N-response relationships were non-significant by familywise error rate criteria. However, some winter crop characteristics, such as rye N accumulation, for which a relationship to seedcotton yield closely approached significance, may merit further research as soil N-supplying capacity bioassays.

Keywords:

• nitrogen
• soil/media testing procedures
• soil fertility

Notes

^†Comparisons of native winter vegetation characteristics to yields of cotton planted following native winter vegetation are included in Scenario 1.

^†Means of plots intended for native winter vegetation.

  ^‡Within a column, means with any trailing letter in common are not significantly different by protected t-test (0.05).

^†Means of plots intended for native winter vegetation.

  ^‡Within a column, means with any trailing letter in common are not significantly different by protected t test (0.05).

^†Within a column and factor, means with any trailing letter in common are not significantly different by protected t test (0.05).

^†Within a column and factor, means with any trailing letter in common are not significantly different by protected t test (0.05).

^†Response variable abbreviations: C_w, yield of cotton planted following winter wheat; C_r, yield of cotton planted following cereal rye; C_n, yield of cotton planted following native winter vegetation; C_f, yield of cotton planted following weed-free winter fallow.

FIGURE 2 Simple linear regression of yield of cotton planted following native winter vegetation (C_n) on rye N accumulation, Saint Joseph, LA, 2005. Data were averaged over replications and paired by 2004 corn N rate. Value of R² found using Microsoft Excel (Microsoft Office Excel 2007, Microsoft Corp., Redmond, WA, USA).

  ^‡Probability-values for explanatory variable coefficients relating wheat characteristics to C_w, rye characteristics to C_r, or native winter vegetation characteristics to C_n pertain to Scenario 1 (Table 1). Probability values for explanatory variable coefficients relating wheat or rye characteristics to C_n or C_f pertain to Scenario 2.