Relative cost to soil fertility of long-term crop production without fertilization

Abstract

An earlier analysis of yield trends of stubble-wheat in six cropping systems, over 35 yr, in a thin Black Chernozemic soil at Indian Head, Saskatchewan, showed that fertilizer improved soil quality, while absence of fertilizer, combined with frequent fallowing, led to soil degradation. The inclusion of a legume green manure crop in the rotation failed to maintain soil fertility, apparently because legumes do not supply P. Because the fertility and stored moisture effects were confounded, we conducted a growth chamber experiment to quantify soil responses to N and P in these six cropping systems. Soil from the top 15-cm of the rotation phase that had just grown two successive wheat (Triticum aestivum L.) crops was used. Various factorial combinations of ammonium nitrate-N and triple superphosphate-P were applied at N/P2O5 rates up to 200/200 kg ha−1. Soil moisture was maintained in the available range. Regression analysis showed that the fallow-wheat-wheat (F-W-W) and continuous wheat (Cont W) systems that had not been fertilized in 35 yr, and which had moderate amounts of NaHCO3-P, only responded to N. In contrast, the green manure (GM)- and hay (H)- containing systems, which had also not been fertilized before had low levels of NaHCO3-P and responded to both N and P. In the field, the yields of wheat grown on stubble in 1991 rated: Cont W (N + P) > F-W-W (N + P) > F-W-W-H-H-H > Cont W > GM-W-W > F-W-W. However, in the growth chamber the rating was: Cont W (N + P) > F-W-W-H-H-H > GM-W-W > Cont W > F-W-W (N + P) > F-W-W. We suggest that the growth chamber results more accurately reflect the present fertility status of these soils, because fertility is no longer confounded with soil moisture. Grain yields in the growth chamber were directly proportional to the previously measured initial potential rate of N mineralization, indicating the value of the latter parameter as a useful index of soil N fertility. Key words: Nitrogen, phosphorus, soil degradation, legumes, fertilizers

Effects of Crop Rotation and Management System on Water‐Extractable Organic Matter Concentration, Structure, and Bioavailability in a Chernozemic Agricultural Soil

“…Although water‐extractable WEOP is a small fraction of soil organic P, our results reveal that WEOP concentration is reduced when incorporating alfalfa in rotations. Similarly, rotations containing sweet clover green manure and bromegrass hay have been reported to have higher rates of P removal and lower concentrations of extractable WEOP in soils (Campbell et al, 1996). Water‐extractable organic P compounds tend to show decreased sorption and increased mobility in soils in comparison to orthophosphate (Bolan et al, 2011).…”

Challenging Approaches to Nitrogen Fertilizer Recommendations in Continuous Cropping Systems in the Great Plains

“…In the same study, the total amount of residue N was 121% greater with annual cropping than in WF, which would increase the potential for N mineralization from plant residues, particularly in fertilized systems. In studies conducted at Indian Head, SK, continuous cropping, compared with fallow systems, increased average yield, organic N, and initial potential rate of N mineralization after 34 yr, particularly where N and P fertilizers were applied (Table 3) (Campbell et al, 1996).…”