Soil nutrient distribution as influenced by crop rotation and fertilization
Based on the agronomic and economic implications of including alfalfa in rotation with annual crops, what is the optimum and annual/perennial crop rotation for producers to utilize?
IPNI-1990-CAN-MB5
24 May 2001
Justification
- Forage production provides potential benefits such as fewer weeds and diseases in subsequent crops, improved soil fertility, tilth and erosion control, extraction of deep leached soil nutrients, and a reduction of the impact of agriculture on the environment.
While most farmers recognize the benefits of including alfalfa in crops rotations, many are reluctant to grow perennial forages because, "They are difficult to establish and they dry out my soil". While this is often the case in the Brown and Dark Brown soil zones of the Canadian prairies, it is not necessarily true for wetter areas. Long-term studies at Indian Head and Melfort, SK (Agric. Canada) showed that rotations including forages for hay are as profitable and pose a lower financial risk than rotations including only annual crops (Campbell et al., 1990; Ag. Can. Publ. 1874/E). Working in Brandon, Manitoba, Bailey (1982, Manitoba Ag. Factsheet; Agdex 537/121) has shown that 5 years of alfalfa reduced the need for fertilizer N in the following 2 barley crops.
Few studies to date have considered the impact of alfalfa stands on extraction of deep-leached nutrients and water. While nitrate leaching can be avoided in many crop production systems (Westerman, 1990; Proc. Great Plains cons. Till Symp., Bismark, ND), N leaching remains a potential hazard for which we must have practical solutions.
Studies in Western Canada have shown that including perennial forages in rotation with annual crops reduces pest problems. For example, Siemens (1963; Cropping Systems: An evaluation of the literature, Faculty of Ag. Publ., U of Manitoba) showed that wheat after two years of hay had only 0.2% dockage while wheat after wheat had 13% dockage. Observations of reduced root rot in wheat after hay compared with wheat after wheat have also been made.
However, two problems with previous research are: 1) forage crops were in the rotation for a fixed period of time, and 2) the annual crops included only cereals. Where different periods of alfalfa seed-down were tested (Ferguson and Gorby, 1971; Can. J. Plant Sci. 51:65-73), only the N contribution of the alfalfa was evaluated (no measures of reduced pests, extraction of deep-leached N, etc. were taken). Therefore, these studies do little to assist farmers in determining the optimum length of an alfalfa stand.
Given the need to reduce input costs, to improve soil quality, and to diversity prairie crop rotations, and given that the demand for high quality alfalfa is growing (Prentice and Jeffrey, 1990; Analysis of exporting of compacted hay from Manitoba; Transport Institute, U of Manitoba), the time to define the optimum period of alfalfa seed-down has never been better. Also, many newer alfalfa cultivars produce much higher yields in the first few years of a stand than traditional cultivars. Hence, shorter rotations may be more profitable today than they were 10 or 20 years ago.