Crop Sequencing to Improve Use of Precipitation and Synergize Crop Growth

Abstract

Cropping systems will not be sustainable without change. Broad‐scope problems associated with developing sustainable cropping systems are how to choose and sequence crops in cropping systems. Our objectives were twofold: (i) evaluate impacts of crop sequencing on precipitation use and (ii) show how crop sequencing can accentuate synergistic interactions among crops. Crop–fallow systems that developed in the Great Plains resulted in precipitation storage efficiencies of about 20% in the early 1930s to about 40% in the late 1980s. Integrated crop–livestock systems have been developed in the southern Great Plains to take advantage of bimodal annual precipitation pattern to produce high quality pigeonpea [Cajanus cajan (L.) Millsp.] forage during the noncrop period between winter wheat (Triticum aestivum L.) harvest and seeding. Pigeonpea can be grown after a mid‐June winter wheat harvest since pigeonpea uses precipitation received from wheat harvest to late September and pigeonpea has a root system that allows it to use soil water below the effective rooting depth of wheat. In the central Great Plains, water‐use efficiency of winter wheat was improved 18 to 56% by including broadleaf crop in a grass‐based rotation. Cropping systems in the northern Great Plains tend to be more diverse, and research at Mandan, ND, suggests that seed yield of flax (Linum usitatissium L.) can be tripled with a safflower (Carthamus tinctorius L.)–flax crop sequence vs. a flax–flax crop sequence. Great Plains cropping systems of the future will not only need to take advantage of crop sequences through synergism, but also take advantage of the interactions associated with diversity in space (polyculture).