White Lupin (Lupinus albus L. cv. Amiga) Increases Solubility of Minjingu Phosphate Rock, Phosphorus Balances and Maize Yields in Njoro Kenya

<p>Exudation of high amounts of citrate in white lupin (<em>Lupinus albus L. cv. Amiga</em>) has the advantage of being effective in mobilization of a wide range of sparingly soluble P sources. To improve cultivation system of maize, a field experiment was conducted to assess effectiveness of white lupin (<em>Lupinus albus</em> L. cv. Amiga) in increasing solubility of minjingu phosphate rock (MPR), phosphorus balances and maize yields in Njoro sub-County, Kenya. The randomized complete block design experiment was conducted for four seasons; short (October – February) and long rain seasons (March-September) of 2010 and 2011. The treatments were; (i) fallow (F) – maize (M) rotation with triple superphosphate (TSP) applied (M_TSP- F), (ii) fallow - maize rotation with MPR applied (M_MPR –F), (iii) lupin (L) – maize rotation with MPR applied (M_MPR- L) and (iv) maize/lupin intercrop with MPR applied (M/L_MPR – F). Soil and plant P and maize grain yield were higher in M/L_MPR – F (with additional lupin grain yield) and M_TSP– F treatments. All treatments resulted in positive P balances at the end of two years with highest values in M_TSP– F treatment and lowest in M/L_MPR – F. Intercropping lupin with maize amid application of MPR is recommended for enhanced maize performance in the farming systems of resource poor farmers. Measurement of available soil nitrogen and comparison of lupin with other legumes in solubilizing MPR is recommended.</p><p> </p>

The Effect of Minjingu Phosphate Rock and Triple Superphosphate on Soil Phosphorus Fractions and Maize Yield in Western Kenya

We tested the effects of triple superphosphate (TSP) and Minjingu phosphate rock (MPR), when applied at phosphorus (P) rates of 50 or 250 kg P ha−1 in a factorial combination with urea or Tithonia diversifolia green manure as nitrogen sources, on P availability and maize yields for two seasons at Nyabeda and Khwisero in Kenya. Phosphorus availability was determined by the Olsen method or sequential fractionation. There was no significant difference in Olsen P as influenced by TSP and MPR at 50 kg P ha−1 irrespective of the N source at both sites in both seasons. However, at 250 kg P ha−1, TSP gave significantly higher Olsen P than MPR. The labile P fractions generally followed the same trend as the Olsen P. Maize yields increased with increasing amount of P applied. Generally, there was no significant difference between TSP and MPR on maize yields irrespective of the N source. The Olsen-P, Resin-P, and sodium bicarbonate inorganic P correlated well with maize yields when TSP was used but the correlations between these P tests and maize yields for MPR were not consistent and therefore their use on soils treated with MPR should be exercised with caution.