View larger version (17K):
[in a new window]
|
Fig. 2. Soil quality and yield response: Example 2a was adapted from Cassman (1999). This depicts the conceptual relationship between yield and input requirements as influenced by soil quality. A decrease in soil quality from an initial state (Ya) can reduce input use efficiency (Yb), yield potential (Yc), or both (Yd). Fig. 2b provides examples of performance outcomes for production potential and nutrient use efficiency in the Morrow Plots, which have been farmed since 1876. Means (1967–1997) are of yield when corn was grown in all plots. Different levels of inputs have been applied to plots maintained under three rotations. Inputs include: none (unamended), manure (approximately 9.9 t ha-1 applied every year to the continuous corn rotation while 13.44 Mg ha-1 are applied before corn in the corn soybean and corn, and corn, oat, hay rotations. Lime and P have also been applied to those plots. Plant density is 19800 plants ha-1 in the manured and unamended plots), manure+ (same amendment rates as those listed above, and plant density is 39600 plants ha-1), NPK (N is applied at 224 kg ha-1 as urea; plots testing <50 and 377 kg ha-1 P and K, respectively, have been amended with 55 and 104 kg ha-1 triple super phosphate and muriate of potash. Plant density is 59400 plants ha-1), MNPK (the manure treatment was applied until 1955, after which N, P, and K and planting density have been applied as listed above), and HNPK (plots that had received the manure treatment until 1967 that have since been amended with only 336 kg N ha-1 as urea; P and K were maintained at test values >125 and 628 kg ha-1 P and K, respectively. Plant density is 59400 plants per ha-1).
|
