william@lorien.newcastle.ac.uk (William Coyne) (11/19/90)
In the past crop rotation without the use of artificial fertilizers was used to maintain the productivity of fields. How did this work? The soil requires various elements - nitrogen, sulphur, phosphorus. Now the nitrogen can be obtained from the atmosphere by growing certain plants in the field(eg clover), but where do the other elements come from to replace those amounts of them used in the previous seasons? email replies can be sent - JANET: W.P.Coyne@uk.ac.newcastle UUCP : ...!ukc!newcastle.ac.uk!W.P.Coyne ARPA : W.P.Coyne%newcastle.ac.uk@nss.cs.ucl.ac.uk
chi9@quads.uchicago.edu (Lucius Chiaraviglio) (11/21/90)
In article <1990Nov19.130439.9168@newcastle.ac.uk> william@lorien.newcastle.ac.uk (William Coyne) writes: >In the past crop rotation without the use of artificial fertilizers >was used to maintain the productivity of fields. > >How did this work? > >The soil requires various elements - nitrogen, sulphur, phosphorus. >Now the nitrogen can be obtained from the atmosphere by growing certain >plants in the field(eg clover), but where do the other elements come >from to replace those amounts of them used in the previous seasons? Well, you see, the sulfur comes from the sulfuric acid in acid rain, and the phosphorus comes from the heavy application of organophosphate pesticides. . . . . . All right, all right, just kidding. Seriously, I think that fertilizer-free soil maintainance schemes must depend upon the application of manure and/or sewage sludge to return the nutrients other than nitrogen (including micronutrients) to the soil, or else depletion does occur eventually. -- | Lucius Chiaraviglio | Internet: chi9@midway.uchicago.edu
jeff@grce.UUCP (Jeff Frank) (11/27/90)
In article <1990Nov19.130439.9168@newcastle.ac.uk> you write: >In the past crop rotation without the use of artificial fertilizers >was used to maintain the productivity of fields. > >How did this work? Nature does not practice monoculture. When man does, some crops can remove nutrients faster than they are provided by weathering of parent material or accumulate in organic matter. By rotating crops time allows the effects of a crop which might be a heavy feeder to be offset by season(s) of crops which do not feed as heavily, or actually add nutrient(s). Maize for example, feeds heavily on nitrogen. The object of growing maize is to feed man or beast. Nutrients are removed from the landscape when the cobs and/or stalks are harvested. Alfalfa planted with rhyzobium innoculant (nitrogen- fixing bacteria) adds nitrogen back to the soil when the alfalfa is plowed under. The nutrients besides nitrogen which have been removed from the landscape as grain or hay must be relaced by weathering of parent material or they will be limitting factors just as if only one crop was grown. "Old" agriculture where crops were rotated, had soils with nutrient levels which could support long term average yields in the range of 30-40 bushels of corn and 2-3 tons of alfalfa. Those were open pollinated varieties. They could respond to added "artificial fertilizers", but not to the degree modern hybrids do. THERE IS NO FREE LUNCH. There is danger in trying to justify the idea that productivity is maintained just by rotating crops. Economics dictate the "old" yields of 30-40 bushels of corn and 2-3 tons of hay per acre probably aren't profitable. > >The soil requires various elements - nitrogen, sulphur, phosphorus. >Now the nitrogen can be obtained from the atmosphere by growing certain >plants in the field(eg clover), but where do the other elements come >from to replace those amounts of them used in the previous seasons? Soil does not require anything. It is a recording of abiotic and biotic activity as parent material is weathered and organic mater accumulates to an equilibrium between gain and loss. The real advantage of crop rotation is that on sloping land, the years in which row crops are not planted, top soil is not being eroded at as fast a rate. This means different things to different soils. In general though erosion of top soil permanently reduces theoretical productivity of the soil. It is not wise to erode soils as one strives to achieve ever higher yields. Also needing consideration is the amount of energy required to make, store, transport, and apply commercial fertilizer. Organic farming types tend to claim otherwise, but in reality, a plant can take nitrogen up in 2 forms ammonium or nitrate. It does not know whether it is from an organic source or applied "chemical fertilizer". Make no mistake about it concentrated commericial fertilizers can and do adversely affect soil in the immediate vicinity to granuals or liquid. This affect is short lived in the presence of adequate moisture. The fertlizers move in solution from areas of high concentration to low concentration. The other nutrients also have no superior organic source. Jeff Frank USENET Email: {rutgers, harvard, ames, uunet}!cs.utexas.edu!uwm!grce!jeff