Soil and plant analyses are diagnostic tools with which the adequacy of soil fertility programs can be evaluated. Plant tissue analysis provides information on what the plant is actually obtaining from the soil and provides a basis for refining the soil fertility program and thus could become an important management tool in crop production. However, as with any analysis, results are of limited value unless factors affecting that analysis are understood and correlations with crop response have been obtained.
The purposes of this study were to determine the effects of cultivar, row spacing and N application rate on nitrate-N (NO3--N) concentration of cotton (Gossypium hirsutum L.) petioles and to assess the applicability of plant analysis for determining the N status of cotton using lint yield as a criterion.
Nitrate-N concentrations were measured in the petioles of cotton plants at intervals during the 1972 and 1973 seasons at three irrigated locations across the southern high plains of Texas. Soils at the southern and central locations were thermic Alfisols (Brownfield Ifs and Amarillo sl, respectively). The soil at the northern location was a thermic Mollisol (Pullman cl). Experimental variables included two cultivars (Paymaster Dwarf and Dunn 56-C), row spacing (1 and 4 rows per 102-cm bed in 1972 and 1, 2, 4 rows per 102-cm bed in 1973), and N application rate (0, 45, 90, 180, and 260 kg/ha).
Cultivar did not exert a consistent influence on the petiole NO3--N concentration measured. The evidence suggested that cultivars found to perform well in narrow row spacings will yield similar petiole NO3--N concentrations when grown under the same cultural and environmental conditions.
Petiole NO3--N concentration at a given stage of growth decreased linearly as row spacing was changed from 1 to 4 rows per 102-cm bed. The effect was greatest during the first half of the growing season on the Brownfield lfs and Amarillo sl soils and during the latter part of the season on the Pullman cl soil. Increasing N application rate increased NO3--N concentration in the petiole. Within a year and location, petiole NO3- N concentration was a sensitive indicator of N application rate. Petiole NO3--N concentration decreased with time throughout the growing season.
Utilization of petiole NO3- -N data to assess the N status of the cotton plant was evaluated by regression of lint yield on the petiole N03--N concentration measured at a given stage of growth. Only a few significant relationships between lint yields and petiole NO3--N concentrations were found, even though N fertilizer affected yields at each location each year. The results indicated that N status could be determined at first bloom on the irrigated coarse-textured soils in the central and southern areas. A year-location interaction occurred, which modified the interpretation placed on the petiole NO3--N concentration measured.
Overall, plant tissue analysis appears to be a valid diagnostic tool for assessing the N status of the cotton plant in the southern great plains. However, before it can be put to general use, a developmental program will have to be conducted for establishment of appropriate correlations.