A field experiment (randomized complete block, factorial) was conducted during 2009 and 2010 in
newly reclaimed sandy soil, New Valley of the western desert, Egypt to assess the interaction effects of
potassium and farmyard manure (FYM) application on growth and soil properties of forage cowpea
(Vigna unguiculata L. local variety). Factors and treatments are: K-application rate: 0, 48, 96 and 144 kg K/ha
(K0, K1, K2 and K3, respectively); K-application timing: pre-seeding during seedbed preparation and postseeding
20 days after seeding (T1 and T2, respectively); FYM rates: 0, 25, 50 and 75 m3/ha (M0, M1, M2 and
M3, respectively). Plant growth and soil property parameters were beneficially affected by K and FYM
application singly or combined. The addition ratio of 1:2:3 for either K or M application rates gave yields of
nearly the same ratios. The lowest yield and NPK uptake were obtained by T1 K0 M0 while, the highest
increases of 130 to 210% were obtained with T1 K3 M3 or T1 K2 M3. Increasing K application from K0 to K1
or K2 decreased the bulk density (BD) ( values being 1.549, 1.539, 1.510 and 1.519 mg/m3 due to K0, K1, K2 and
K3 respectively). Increasing FYM increased BD (values being 1.615, 1.520, 1.495 and 1.490 mg/m3 due to M0,
M1, M2 and M3, respectively). Field capacity (FC) and available water (AW) increased with increasing both
K and FYM. FC = 10.81, 11.90, 13.47 and 15.91% due to K0, K1, K2 and K3, respectively; 9.72, 13.05, 14.75 and
15.73 % due to M0, M1, M2 and M3, respectively. AW = 9.37, 12.43, 12.07 and 13.61 % for K0, K1, K2 and K3,
respectively.