MULTIPURPOSE TREE PRUNINGS AS A SOURCE OF NITROGEN TO MAIZE UNDER SEMIARID CONDITIONS IN ZIMBABWE .2. NITROGEN-RECOVERY RATES AND CROP GROWTH AS INFLUENCED BY MIXTURES AND PRUNINGS

Time of pruning application and mixing prunings of varying qualities c ould be important management options to increase the rate of nitrogen recovery from multipurpose-tree prunings that are used as a source of nitrogen to crops. A field experiment was conducted in the semiarid zo ne of Zimbabwe to test this hypothesis, using prunings of calliandra ( Calliandra calothyrsus) and leucaena (Leucaena leucocephala), alone an d in mixtures, and maize (Zea mays) as the test crop. Time of pruning application significantly improved N uptake, N recovery, and grain yie ld of maize. Applying prunings of calliandra at maize planting was sig nificantly better in terms of N uptake, N recovery, and grain yield th an applying them four weeks after planting. However, with leucaena, ti me of prunings application had no significant effects on;N recovery. M ixing prunings of leucaena and calliandra had no effect on maize N upt ake, N recovery, and grain yield. Split application of available pruni ngs during the crop growth cycle had no effect on N recovery compared to one-time application of entire amounts of prunings at planting.